mod.rs

/*!
Backend for [GLSL][glsl] (OpenGL Shading Language).

The main structure is [`Writer`], it maintains internal state that is used
to output a [`Module`](crate::Module) into glsl

# Supported versions
### Core
- 330
- 400
- 410
- 420
- 430
- 450

### ES
- 300
- 310

[glsl]: https://www.khronos.org/registry/OpenGL/index_gl.php
*/

// GLSL is mostly a superset of C but it also removes some parts of it this is a list of relevant
// aspects for this backend.
//
// The most notable change is the introduction of the version preprocessor directive that must
// always be the first line of a glsl file and is written as
// `#version number profile`
// `number` is the version itself (i.e. 300) and `profile` is the
// shader profile we only support "core" and "es", the former is used in desktop applications and
// the later is used in embedded contexts, mobile devices and browsers. Each one as it's own
// versions (at the time of writing this the latest version for "core" is 460 and for "es" is 320)
//
// Other important preprocessor addition is the extension directive which is written as
// `#extension name: behaviour`
// Extensions provide increased features in a plugin fashion but they aren't required to be
// supported hence why they are called extensions, that's why `behaviour` is used it specifies
// whether the extension is strictly required or if it should only be enabled if needed. In our case
// when we use extensions we set behaviour to `require` always.
//
// The only thing that glsl removes that makes a difference are pointers.
//
// Additions that are relevant for the backend are the discard keyword, the introduction of
// vector, matrices, samplers, image types and functions that provide common shader operations

pub use features::Features;

use crate::{
    back,
    proc::{self, NameKey},
    valid, Handle, ShaderStage, TypeInner,
};
use features::FeaturesManager;
use std::{
    cmp::Ordering,
    fmt,
    fmt::{Error as FmtError, Write},
};
use thiserror::Error;

/// Contains the features related code and the features querying method
mod features;
/// Contains a constant with a slice of all the reserved keywords RESERVED_KEYWORDS
mod keywords;

/// List of supported `core` GLSL versions.
pub const SUPPORTED_CORE_VERSIONS: &[u16] = &[330, 400, 410, 420, 430, 440, 450];
/// List of supported `es` GLSL versions.
pub const SUPPORTED_ES_VERSIONS: &[u16] = &[300, 310, 320];

/// The suffix of the variable that will hold the calculated clamped level
/// of detail for bounds checking in `ImageLoad`
const CLAMPED_LOD_SUFFIX: &str = "_clamped_lod";

pub(crate) const MODF_FUNCTION: &str = "naga_modf";
pub(crate) const FREXP_FUNCTION: &str = "naga_frexp";

/// Mapping between resources and bindings.
pub type BindingMap = std::collections::BTreeMap<crate::ResourceBinding, u8>;

impl crate::AtomicFunction {
    const fn to_glsl(self) -> &'static str {
        match self {
            Self::Add | Self::Subtract => "Add",
            Self::And => "And",
            Self::InclusiveOr => "Or",
            Self::ExclusiveOr => "Xor",
            Self::Min => "Min",
            Self::Max => "Max",
            Self::Exchange { compare: None } => "Exchange",
            Self::Exchange { compare: Some(_) } => "", //TODO
        }
    }
}

impl crate::AddressSpace {
    const fn is_buffer(&self) -> bool {
        match *self {
            crate::AddressSpace::Uniform | crate::AddressSpace::Storage { .. } => true,
            _ => false,
        }
    }

    /// Whether a variable with this address space can be initialized
    const fn initializable(&self) -> bool {
        match *self {
            crate::AddressSpace::Function | crate::AddressSpace::Private => true,
            crate::AddressSpace::WorkGroup
            | crate::AddressSpace::Uniform
            | crate::AddressSpace::Storage { .. }
            | crate::AddressSpace::Handle
            | crate::AddressSpace::PushConstant => false,
        }
    }
}

/// A GLSL version.
#[derive(Debug, Copy, Clone, PartialEq)]
#[cfg_attr(feature = "serialize", derive(serde::Serialize))]
#[cfg_attr(feature = "deserialize", derive(serde::Deserialize))]
pub enum Version {
    /// `core` GLSL.
    Desktop(u16),
    /// `es` GLSL.
    Embedded { version: u16, is_webgl: bool },
}

impl Version {
    /// Create a new gles version
    pub const fn new_gles(version: u16) -> Self {
        Self::Embedded {
            version,
            is_webgl: false,
        }
    }

    /// Returns true if self is `Version::Embedded` (i.e. is a es version)
    const fn is_es(&self) -> bool {
        match *self {
            Version::Desktop(_) => false,
            Version::Embedded { .. } => true,
        }
    }

    /// Returns true if targetting WebGL
    const fn is_webgl(&self) -> bool {
        match *self {
            Version::Desktop(_) => false,
            Version::Embedded { is_webgl, .. } => is_webgl,
        }
    }

    /// Checks the list of currently supported versions and returns true if it contains the
    /// specified version
    ///
    /// # Notes
    /// As an invalid version number will never be added to the supported version list
    /// so this also checks for version validity
    fn is_supported(&self) -> bool {
        match *self {
            Version::Desktop(v) => SUPPORTED_CORE_VERSIONS.contains(&v),
            Version::Embedded { version: v, .. } => SUPPORTED_ES_VERSIONS.contains(&v),
        }
    }

    /// Checks if the version supports all of the explicit layouts:
    /// - `location=` qualifiers for bindings
    /// - `binding=` qualifiers for resources
    ///
    /// Note: `location=` for vertex inputs and fragment outputs is supported
    /// unconditionally for GLES 300.
    fn supports_explicit_locations(&self) -> bool {
        *self >= Version::Desktop(410) || *self >= Version::new_gles(310)
    }

    fn supports_early_depth_test(&self) -> bool {
        *self >= Version::Desktop(130) || *self >= Version::new_gles(310)
    }

    fn supports_std430_layout(&self) -> bool {
        *self >= Version::Desktop(430) || *self >= Version::new_gles(310)
    }

    fn supports_fma_function(&self) -> bool {
        *self >= Version::Desktop(400) || *self >= Version::new_gles(320)
    }

    fn supports_integer_functions(&self) -> bool {
        *self >= Version::Desktop(400) || *self >= Version::new_gles(310)
    }

    fn supports_frexp_function(&self) -> bool {
        *self >= Version::Desktop(400) || *self >= Version::new_gles(310)
    }

    fn supports_derivative_control(&self) -> bool {
        *self >= Version::Desktop(450)
    }
}

impl PartialOrd for Version {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        match (*self, *other) {
            (Version::Desktop(x), Version::Desktop(y)) => Some(x.cmp(&y)),
            (Version::Embedded { version: x, .. }, Version::Embedded { version: y, .. }) => {
                Some(x.cmp(&y))
            }
            _ => None,
        }
    }
}

impl fmt::Display for Version {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match *self {
            Version::Desktop(v) => write!(f, "{v} core"),
            Version::Embedded { version: v, .. } => write!(f, "{v} es"),
        }
    }
}

bitflags::bitflags! {
    /// Configuration flags for the [`Writer`].
    #[cfg_attr(feature = "serialize", derive(serde::Serialize))]
    #[cfg_attr(feature = "deserialize", derive(serde::Deserialize))]
    #[derive(Clone, Copy, Debug, Eq, PartialEq)]
    pub struct WriterFlags: u32 {
        /// Flip output Y and extend Z from (0, 1) to (-1, 1).
        const ADJUST_COORDINATE_SPACE = 0x1;
        /// Supports GL_EXT_texture_shadow_lod on the host, which provides
        /// additional functions on shadows and arrays of shadows.
        const TEXTURE_SHADOW_LOD = 0x2;
        /// Include unused global variables, constants and functions. By default the output will exclude
        /// global variables that are not used in the specified entrypoint (including indirect use),
        /// all constant declarations, and functions that use excluded global variables.
        const INCLUDE_UNUSED_ITEMS = 0x4;
        /// Emit `PointSize` output builtin to vertex shaders, which is
        /// required for drawing with `PointList` topology.
        ///
        /// https://registry.khronos.org/OpenGL/specs/es/3.2/GLSL_ES_Specification_3.20.html#built-in-language-variables
        /// The variable gl_PointSize is intended for a shader to write the size of the point to be rasterized. It is measured in pixels.
        /// If gl_PointSize is not written to, its value is undefined in subsequent pipe stages.
        const FORCE_POINT_SIZE = 0x10;
    }
}

/// Configuration used in the [`Writer`].
#[derive(Debug, Clone)]
#[cfg_attr(feature = "serialize", derive(serde::Serialize))]
#[cfg_attr(feature = "deserialize", derive(serde::Deserialize))]
pub struct Options {
    /// The GLSL version to be used.
    pub version: Version,
    /// Configuration flags for the [`Writer`].
    pub writer_flags: WriterFlags,
    /// Map of resources association to binding locations.
    pub binding_map: BindingMap,
    /// Should workgroup variables be zero initialized (by polyfilling)?
    pub zero_initialize_workgroup_memory: bool,
}

impl Default for Options {
    fn default() -> Self {
        Options {
            version: Version::new_gles(310),
            writer_flags: WriterFlags::ADJUST_COORDINATE_SPACE,
            binding_map: BindingMap::default(),
            zero_initialize_workgroup_memory: true,
        }
    }
}

/// A subset of options meant to be changed per pipeline.
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
#[cfg_attr(feature = "serialize", derive(serde::Serialize))]
#[cfg_attr(feature = "deserialize", derive(serde::Deserialize))]
pub struct PipelineOptions {
    /// The stage of the entry point.
    pub shader_stage: ShaderStage,
    /// The name of the entry point.
    ///
    /// If no entry point that matches is found while creating a [`Writer`], a error will be thrown.
    pub entry_point: String,
    /// How many views to render to, if doing multiview rendering.
    pub multiview: Option<std::num::NonZeroU32>,
}

/// Reflection info for texture mappings and uniforms.
pub struct ReflectionInfo {
    /// Mapping between texture names and variables/samplers.
    pub texture_mapping: crate::FastHashMap<String, TextureMapping>,
    /// Mapping between uniform variables and names.
    pub uniforms: crate::FastHashMap<Handle<crate::GlobalVariable>, String>,
}

/// Mapping between a texture and its sampler, if it exists.
///
/// GLSL pre-Vulkan has no concept of separate textures and samplers. Instead, everything is a
/// `gsamplerN` where `g` is the scalar type and `N` is the dimension. But naga uses separate textures
/// and samplers in the IR, so the backend produces a [`FastHashMap`](crate::FastHashMap) with the texture name
/// as a key and a [`TextureMapping`] as a value. This way, the user knows where to bind.
///
/// [`Storage`](crate::ImageClass::Storage) images produce `gimageN` and don't have an associated sampler,
/// so the [`sampler`](Self::sampler) field will be [`None`].
#[derive(Debug, Clone)]
pub struct TextureMapping {
    /// Handle to the image global variable.
    pub texture: Handle<crate::GlobalVariable>,
    /// Handle to the associated sampler global variable, if it exists.
    pub sampler: Option<Handle<crate::GlobalVariable>>,
}

/// Helper structure that generates a number
#[derive(Default)]
struct IdGenerator(u32);

impl IdGenerator {
    /// Generates a number that's guaranteed to be unique for this `IdGenerator`
    fn generate(&mut self) -> u32 {
        // It's just an increasing number but it does the job
        let ret = self.0;
        self.0 += 1;
        ret
    }
}

/// Helper wrapper used to get a name for a varying
///
/// Varying have different naming schemes depending on their binding:
/// - Varyings with builtin bindings get the from [`glsl_built_in`](glsl_built_in).
/// - Varyings with location bindings are named `_S_location_X` where `S` is a
///   prefix identifying which pipeline stage the varying connects, and `X` is
///   the location.
struct VaryingName<'a> {
    binding: &'a crate::Binding,
    stage: ShaderStage,
    output: bool,
    targetting_webgl: bool,
}
impl fmt::Display for VaryingName<'_> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match *self.binding {
            crate::Binding::Location {
                second_blend_source: true,
                ..
            } => {
                write!(f, "_fs2p_location1",)
            }
            crate::Binding::Location { location, .. } => {
                let prefix = match (self.stage, self.output) {
                    (ShaderStage::Compute, _) => unreachable!(),
                    // pipeline to vertex
                    (ShaderStage::Vertex, false) => "p2vs",
                    // vertex to fragment
                    (ShaderStage::Vertex, true) | (ShaderStage::Fragment, false) => "vs2fs",
                    // fragment to pipeline
                    (ShaderStage::Fragment, true) => "fs2p",
                };
                write!(f, "_{prefix}_location{location}",)
            }
            crate::Binding::BuiltIn(built_in) => {
                write!(
                    f,
                    "{}",
                    glsl_built_in(built_in, self.output, self.targetting_webgl)
                )
            }
        }
    }
}

impl ShaderStage {
    const fn to_str(self) -> &'static str {
        match self {
            ShaderStage::Compute => "cs",
            ShaderStage::Fragment => "fs",
            ShaderStage::Vertex => "vs",
        }
    }
}

/// Shorthand result used internally by the backend
type BackendResult<T = ()> = Result<T, Error>;

/// A GLSL compilation error.
#[derive(Debug, Error)]
pub enum Error {
    /// A error occurred while writing to the output.
    #[error("Format error")]
    FmtError(#[from] FmtError),
    /// The specified [`Version`] doesn't have all required [`Features`].
    ///
    /// Contains the missing [`Features`].
    #[error("The selected version doesn't support {0:?}")]
    MissingFeatures(Features),
    /// [`AddressSpace::PushConstant`](crate::AddressSpace::PushConstant) was used more than
    /// once in the entry point, which isn't supported.
    #[error("Multiple push constants aren't supported")]
    MultiplePushConstants,
    /// The specified [`Version`] isn't supported.
    #[error("The specified version isn't supported")]
    VersionNotSupported,
    /// The entry point couldn't be found.
    #[error("The requested entry point couldn't be found")]
    EntryPointNotFound,
    /// A call was made to an unsupported external.
    #[error("A call was made to an unsupported external: {0}")]
    UnsupportedExternal(String),
    /// A scalar with an unsupported width was requested.
    #[error("A scalar with an unsupported width was requested: {0:?} {1:?}")]
    UnsupportedScalar(crate::ScalarKind, crate::Bytes),
    /// A image was used with multiple samplers, which isn't supported.
    #[error("A image was used with multiple samplers")]
    ImageMultipleSamplers,
    #[error("{0}")]
    Custom(String),
}

/// Binary operation with a different logic on the GLSL side.
enum BinaryOperation {
    /// Vector comparison should use the function like `greaterThan()`, etc.
    VectorCompare,
    /// Vector component wise operation; used to polyfill unsupported ops like `|` and `&` for `bvecN`'s
    VectorComponentWise,
    /// GLSL `%` is SPIR-V `OpUMod/OpSMod` and `mod()` is `OpFMod`, but [`BinaryOperator::Modulo`](crate::BinaryOperator::Modulo) is `OpFRem`.
    Modulo,
    /// Any plain operation. No additional logic required.
    Other,
}

/// Writer responsible for all code generation.
pub struct Writer<'a, W> {
    // Inputs
    /// The module being written.
    module: &'a crate::Module,
    /// The module analysis.
    info: &'a valid::ModuleInfo,
    /// The output writer.
    out: W,
    /// User defined configuration to be used.
    options: &'a Options,
    /// The bound checking policies to be used
    policies: proc::BoundsCheckPolicies,

    // Internal State
    /// Features manager used to store all the needed features and write them.
    features: FeaturesManager,
    namer: proc::Namer,
    /// A map with all the names needed for writing the module
    /// (generated by a [`Namer`](crate::proc::Namer)).
    names: crate::FastHashMap<NameKey, String>,
    /// A map with the names of global variables needed for reflections.
    reflection_names_globals: crate::FastHashMap<Handle<crate::GlobalVariable>, String>,
    /// The selected entry point.
    entry_point: &'a crate::EntryPoint,
    /// The index of the selected entry point.
    entry_point_idx: proc::EntryPointIndex,
    /// A generator for unique block numbers.
    block_id: IdGenerator,
    /// Set of expressions that have associated temporary variables.
    named_expressions: crate::NamedExpressions,
    /// Set of expressions that need to be baked to avoid unnecessary repetition in output
    need_bake_expressions: back::NeedBakeExpressions,
    /// How many views to render to, if doing multiview rendering.
    multiview: Option<std::num::NonZeroU32>,
}

impl<'a, W: Write> Writer<'a, W> {
    /// Creates a new [`Writer`] instance.
    ///
    /// # Errors
    /// - If the version specified is invalid or supported.
    /// - If the entry point couldn't be found in the module.
    /// - If the version specified doesn't support some used features.
    pub fn new(
        out: W,
        module: &'a crate::Module,
        info: &'a valid::ModuleInfo,
        options: &'a Options,
        pipeline_options: &'a PipelineOptions,
        policies: proc::BoundsCheckPolicies,
    ) -> Result<Self, Error> {
        // Check if the requested version is supported
        if !options.version.is_supported() {
            log::error!("Version {}", options.version);
            return Err(Error::VersionNotSupported);
        }

        // Try to find the entry point and corresponding index
        let ep_idx = module
            .entry_points
            .iter()
            .position(|ep| {
                pipeline_options.shader_stage == ep.stage && pipeline_options.entry_point == ep.name
            })
            .ok_or(Error::EntryPointNotFound)?;

        // Generate a map with names required to write the module
        let mut names = crate::FastHashMap::default();
        let mut namer = proc::Namer::default();
        namer.reset(
            module,
            keywords::RESERVED_KEYWORDS,
            &[],
            &[],
            &["gl_"],
            &mut names,
        );

        // Build the instance
        let mut this = Self {
            module,
            info,
            out,
            options,
            policies,

            namer,
            features: FeaturesManager::new(),
            names,
            reflection_names_globals: crate::FastHashMap::default(),
            entry_point: &module.entry_points[ep_idx],
            entry_point_idx: ep_idx as u16,
            multiview: pipeline_options.multiview,
            block_id: IdGenerator::default(),
            named_expressions: Default::default(),
            need_bake_expressions: Default::default(),
        };

        // Find all features required to print this module
        this.collect_required_features()?;

        Ok(this)
    }

    /// Writes the [`Module`](crate::Module) as glsl to the output
    ///
    /// # Notes
    /// If an error occurs while writing, the output might have been written partially
    ///
    /// # Panics
    /// Might panic if the module is invalid
    pub fn write(&mut self) -> Result<ReflectionInfo, Error> {
        // We use `writeln!(self.out)` throughout the write to add newlines
        // to make the output more readable

        let es = self.options.version.is_es();

        // Write the version (It must be the first thing or it isn't a valid glsl output)
        writeln!(self.out, "#version {}", self.options.version)?;
        // Write all the needed extensions
        //
        // This used to be the last thing being written as it allowed to search for features while
        // writing the module saving some loops but some older versions (420 or less) required the
        // extensions to appear before being used, even though extensions are part of the
        // preprocessor not the processor ¯\_(ツ)_/¯
        self.features.write(self.options.version, &mut self.out)?;

        // Write the additional extensions
        if self
            .options
            .writer_flags
            .contains(WriterFlags::TEXTURE_SHADOW_LOD)
        {
            // https://www.khronos.org/registry/OpenGL/extensions/EXT/EXT_texture_shadow_lod.txt
            writeln!(self.out, "#extension GL_EXT_texture_shadow_lod : require")?;
        }

        // glsl es requires a precision to be specified for floats and ints
        // TODO: Should this be user configurable?
        if es {
            writeln!(self.out)?;
            writeln!(self.out, "precision highp float;")?;
            writeln!(self.out, "precision highp int;")?;
            writeln!(self.out)?;
        }

        if self.entry_point.stage == ShaderStage::Compute {
            let workgroup_size = self.entry_point.workgroup_size;
            writeln!(
                self.out,
                "layout(local_size_x = {}, local_size_y = {}, local_size_z = {}) in;",
                workgroup_size[0], workgroup_size[1], workgroup_size[2]
            )?;
            writeln!(self.out)?;
        }

        // Enable early depth tests if needed
        if let Some(depth_test) = self.entry_point.early_depth_test {
            // If early depth test is supported for this version of GLSL
            if self.options.version.supports_early_depth_test() {
                writeln!(self.out, "layout(early_fragment_tests) in;")?;

                if let Some(conservative) = depth_test.conservative {
                    use crate::ConservativeDepth as Cd;

                    let depth = match conservative {
                        Cd::GreaterEqual => "greater",
                        Cd::LessEqual => "less",
                        Cd::Unchanged => "unchanged",
                    };
                    writeln!(self.out, "layout (depth_{depth}) out float gl_FragDepth;")?;
                }
                writeln!(self.out)?;
            } else {
                log::warn!(
                    "Early depth testing is not supported for this version of GLSL: {}",
                    self.options.version
                );
            }
        }

        if self.entry_point.stage == ShaderStage::Vertex && self.options.version.is_webgl() {
            if let Some(multiview) = self.multiview.as_ref() {
                writeln!(self.out, "layout(num_views = {multiview}) in;")?;
                writeln!(self.out)?;
            }
        }

        // Write struct types.
        //
        // This are always ordered because the IR is structured in a way that
        // you can't make a struct without adding all of its members first.
        for (handle, ty) in self.module.types.iter() {
            if let TypeInner::Struct { ref members, .. } = ty.inner {
                // Structures ending with runtime-sized arrays can only be
                // rendered as shader storage blocks in GLSL, not stand-alone
                // struct types.
                if !self.module.types[members.last().unwrap().ty]
                    .inner
                    .is_dynamically_sized(&self.module.types)
                {
                    let name = &self.names[&NameKey::Type(handle)];
                    write!(self.out, "struct {name} ")?;
                    self.write_struct_body(handle, members)?;
                    writeln!(self.out, ";")?;
                }
            }
        }

        // Write functions to create special types.
        for (type_key, struct_ty) in self.module.special_types.predeclared_types.iter() {
            match type_key {
                &crate::PredeclaredType::ModfResult { size, width }
                | &crate::PredeclaredType::FrexpResult { size, width } => {
                    let arg_type_name_owner;
                    let arg_type_name = if let Some(size) = size {
                        arg_type_name_owner =
                            format!("{}vec{}", if width == 8 { "d" } else { "" }, size as u8);
                        &arg_type_name_owner
                    } else if width == 8 {
                        "double"
                    } else {
                        "float"
                    };

                    let other_type_name_owner;
                    let (defined_func_name, called_func_name, other_type_name) =
                        if matches!(type_key, &crate::PredeclaredType::ModfResult { .. }) {
                            (MODF_FUNCTION, "modf", arg_type_name)
                        } else {
                            let other_type_name = if let Some(size) = size {
                                other_type_name_owner = format!("ivec{}", size as u8);
                                &other_type_name_owner
                            } else {
                                "int"
                            };
                            (FREXP_FUNCTION, "frexp", other_type_name)
                        };

                    let struct_name = &self.names[&NameKey::Type(*struct_ty)];

                    writeln!(self.out)?;
                    if !self.options.version.supports_frexp_function()
                        && matches!(type_key, &crate::PredeclaredType::FrexpResult { .. })
                    {
                        writeln!(
                            self.out,
                            "{struct_name} {defined_func_name}({arg_type_name} arg) {{
    {other_type_name} other = arg == {arg_type_name}(0) ? {other_type_name}(0) : {other_type_name}({arg_type_name}(1) + log2(arg));
    {arg_type_name} fract = arg * exp2({arg_type_name}(-other));
    return {struct_name}(fract, other);
}}",
                        )?;
                    } else {
                        writeln!(
                            self.out,
                            "{struct_name} {defined_func_name}({arg_type_name} arg) {{
    {other_type_name} other;
    {arg_type_name} fract = {called_func_name}(arg, other);
    return {struct_name}(fract, other);
}}",
                        )?;
                    }
                }
                &crate::PredeclaredType::AtomicCompareExchangeWeakResult { .. } => {}
            }
        }

        // Write all named constants
        let mut constants = self
            .module
            .constants
            .iter()
            .filter(|&(_, c)| c.name.is_some())
            .peekable();
        while let Some((handle, _)) = constants.next() {
            self.write_global_constant(handle)?;
            // Add extra newline for readability on last iteration
            if constants.peek().is_none() {
                writeln!(self.out)?;
            }
        }

        let ep_info = self.info.get_entry_point(self.entry_point_idx as usize);

        // Write the globals
        //
        // Unless explicitly disabled with WriterFlags::INCLUDE_UNUSED_ITEMS,
        // we filter all globals that aren't used by the selected entry point as they might be
        // interfere with each other (i.e. two globals with the same location but different with
        // different classes)
        let include_unused = self
            .options
            .writer_flags
            .contains(WriterFlags::INCLUDE_UNUSED_ITEMS);
        for (handle, global) in self.module.global_variables.iter() {
            let is_unused = ep_info[handle].is_empty();
            if !include_unused && is_unused {
                continue;
            }

            match self.module.types[global.ty].inner {
                // We treat images separately because they might require
                // writing the storage format
                TypeInner::Image {
                    mut dim,
                    arrayed,
                    class,
                } => {
                    // Gather the storage format if needed
                    let storage_format_access = match self.module.types[global.ty].inner {
                        TypeInner::Image {
                            class: crate::ImageClass::Storage { format, access },
                            ..
                        } => Some((format, access)),
                        _ => None,
                    };

                    if dim == crate::ImageDimension::D1 && es {
                        dim = crate::ImageDimension::D2
                    }

                    // Gether the location if needed
                    let layout_binding = if self.options.version.supports_explicit_locations() {
                        let br = global.binding.as_ref().unwrap();
                        self.options.binding_map.get(br).cloned()
                    } else {
                        None
                    };

                    // Write all the layout qualifiers
                    if layout_binding.is_some() || storage_format_access.is_some() {
                        write!(self.out, "layout(")?;
                        if let Some(binding) = layout_binding {
                            write!(self.out, "binding = {binding}")?;
                        }
                        if let Some((format, _)) = storage_format_access {
                            let format_str = glsl_storage_format(format)?;
                            let separator = match layout_binding {
                                Some(_) => ",",
                                None => "",
                            };
                            write!(self.out, "{separator}{format_str}")?;
                        }
                        write!(self.out, ") ")?;
                    }

                    if let Some((_, access)) = storage_format_access {
                        self.write_storage_access(access)?;
                    }

                    // All images in glsl are `uniform`
                    // The trailing space is important
                    write!(self.out, "uniform ")?;

                    // write the type
                    //
                    // This is way we need the leading space because `write_image_type` doesn't add
                    // any spaces at the beginning or end
                    self.write_image_type(dim, arrayed, class)?;

                    // Finally write the name and end the global with a `;`
                    // The leading space is important
                    let global_name = self.get_global_name(handle, global);
                    writeln!(self.out, " {global_name};")?;
                    writeln!(self.out)?;

                    self.reflection_names_globals.insert(handle, global_name);
                }
                // glsl has no concept of samplers so we just ignore it
                TypeInner::Sampler { .. } => continue,
                // All other globals are written by `write_global`
                _ => {
                    self.write_global(handle, global)?;
                    // Add a newline (only for readability)
                    writeln!(self.out)?;
                }
            }
        }

        for arg in self.entry_point.function.arguments.iter() {
            self.write_varying(arg.binding.as_ref(), arg.ty, false)?;
        }
        if let Some(ref result) = self.entry_point.function.result {
            self.write_varying(result.binding.as_ref(), result.ty, true)?;
        }
        writeln!(self.out)?;

        // Write all regular functions
        for (handle, function) in self.module.functions.iter() {
            // Check that the function doesn't use globals that aren't supported
            // by the current entry point
            if !include_unused && !ep_info.dominates_global_use(&self.info[handle]) {
                continue;
            }

            let fun_info = &self.info[handle];

            // Skip functions that that are not compatible with this entry point's stage.
            //
            // When validation is enabled, it rejects modules whose entry points try to call
            // incompatible functions, so if we got this far, then any functions incompatible
            // with our selected entry point must not be used.
            //
            // When validation is disabled, `fun_info.available_stages` is always just
            // `ShaderStages::all()`, so this will write all functions in the module, and
            // the downstream GLSL compiler will catch any problems.
            if !fun_info.available_stages.contains(ep_info.available_stages) {
                continue;
            }

            // Write the function
            self.write_function(back::FunctionType::Function(handle), function, fun_info)?;

            writeln!(self.out)?;
        }

        self.write_function(
            back::FunctionType::EntryPoint(self.entry_point_idx),
            &self.entry_point.function,
            ep_info,
        )?;

        // Add newline at the end of file
        writeln!(self.out)?;

        // Collect all reflection info and return it to the user
        self.collect_reflection_info()
    }

    fn write_array_size(
        &mut self,
        base: Handle<crate::Type>,
        size: crate::ArraySize,
    ) -> BackendResult {
        write!(self.out, "[")?;

        // Write the array size
        // Writes nothing if `ArraySize::Dynamic`
        match size {
            crate::ArraySize::Constant(size) => {
                write!(self.out, "{size}")?;
            }
            crate::ArraySize::Dynamic => (),
        }

        write!(self.out, "]")?;

        if let TypeInner::Array {
            base: next_base,
            size: next_size,
            ..
        } = self.module.types[base].inner
        {
            self.write_array_size(next_base, next_size)?;
        }

        Ok(())
    }

    /// Helper method used to write value types
    ///
    /// # Notes
    /// Adds no trailing or leading whitespace
    fn write_value_type(&mut self, inner: &TypeInner) -> BackendResult {
        match *inner {
            // Scalars are simple we just get the full name from `glsl_scalar`
            TypeInner::Scalar { kind, width }
            | TypeInner::Atomic { kind, width }
            | TypeInner::ValuePointer {
                size: None,
                kind,
                width,
                space: _,
            } => write!(self.out, "{}", glsl_scalar(kind, width)?.full)?,
            // Vectors are just `gvecN` where `g` is the scalar prefix and `N` is the vector size
            TypeInner::Vector { size, kind, width }
            | TypeInner::ValuePointer {
                size: Some(size),
                kind,
                width,
                space: _,
            } => write!(
                self.out,
                "{}vec{}",
                glsl_scalar(kind, width)?.prefix,
                size as u8
            )?,
            // Matrices are written with `gmatMxN` where `g` is the scalar prefix (only floats and
            // doubles are allowed), `M` is the columns count and `N` is the rows count
            //
            // glsl supports a matrix shorthand `gmatN` where `N` = `M` but it doesn't justify the
            // extra branch to write matrices this way
            TypeInner::Matrix {
                columns,
                rows,
                width,
            } => write!(
                self.out,
                "{}mat{}x{}",
                glsl_scalar(crate::ScalarKind::Float, width)?.prefix,
                columns as u8,
                rows as u8
            )?,
            // GLSL arrays are written as `type name[size]`
            // Here we only write the size of the array i.e. `[size]`
            // Base `type` and `name` should be written outside
            TypeInner::Array { base, size, .. } => self.write_array_size(base, size)?,
            // Write all variants instead of `_` so that if new variants are added a
            // no exhaustiveness error is thrown
            TypeInner::Pointer { .. }
            | TypeInner::Struct { .. }
            | TypeInner::Image { .. }
            | TypeInner::Sampler { .. }
            | TypeInner::AccelerationStructure
            | TypeInner::RayQuery
            | TypeInner::BindingArray { .. } => {
                return Err(Error::Custom(format!("Unable to write type {inner:?}")))
            }
        }

        Ok(())
    }

    /// Helper method used to write non image/sampler types
    ///
    /// # Notes
    /// Adds no trailing or leading whitespace
    fn write_type(&mut self, ty: Handle<crate::Type>) -> BackendResult {
        match self.module.types[ty].inner {
            // glsl has no pointer types so just write types as normal and loads are skipped
            TypeInner::Pointer { base, .. } => self.write_type(base),
            // glsl structs are written as just the struct name
            TypeInner::Struct { .. } => {
                // Get the struct name
                let name = &self.names[&NameKey::Type(ty)];
                write!(self.out, "{name}")?;
                Ok(())
            }
            // glsl array has the size separated from the base type
            TypeInner::Array { base, .. } => self.write_type(base),
            ref other => self.write_value_type(other),
        }
    }

    /// Helper method to write a image type
    ///
    /// # Notes
    /// Adds no leading or trailing whitespace
    fn write_image_type(
        &mut self,
        dim: crate::ImageDimension,
        arrayed: bool,
        class: crate::ImageClass,
    ) -> BackendResult {
        // glsl images consist of four parts the scalar prefix, the image "type", the dimensions
        // and modifiers
        //
        // There exists two image types
        // - sampler - for sampled images
        // - image - for storage images
        //
        // There are three possible modifiers that can be used together and must be written in
        // this order to be valid
        // - MS - used if it's a multisampled image
        // - Array - used if it's an image array
        // - Shadow - used if it's a depth image
        use crate::ImageClass as Ic;

        let (base, kind, ms, comparison) = match class {
            Ic::Sampled { kind, multi: true } => ("sampler", kind, "MS", ""),
            Ic::Sampled { kind, multi: false } => ("sampler", kind, "", ""),
            Ic::Depth { multi: true } => ("sampler", crate::ScalarKind::Float, "MS", ""),
            Ic::Depth { multi: false } => ("sampler", crate::ScalarKind::Float, "", "Shadow"),
            Ic::Storage { format, .. } => ("image", format.into(), "", ""),
        };

        write!(
            self.out,
            "highp {}{}{}{}{}{}",
            glsl_scalar(kind, 4)?.prefix,
            base,
            glsl_dimension(dim),
            ms,
            if arrayed { "Array" } else { "" },
            comparison
        )?;

        Ok(())
    }

    /// Helper method used to write non images/sampler globals
    ///
    /// # Notes
    /// Adds a newline
    ///
    /// # Panics
    /// If the global has type sampler
    fn write_global(
        &mut self,
        handle: Handle<crate::GlobalVariable>,
        global: &crate::GlobalVariable,
    ) -> BackendResult {
        if self.options.version.supports_explicit_locations() {
            if let Some(ref br) = global.binding {
                match self.options.binding_map.get(br) {
                    Some(binding) => {
                        let layout = match global.space {
                            crate::AddressSpace::Storage { .. } => {
                                if self.options.version.supports_std430_layout() {
                                    "std430, "
                                } else {
                                    "std140, "
                                }
                            }
                            crate::AddressSpace::Uniform => "std140, ",
                            _ => "",
                        };
                        write!(self.out, "layout({layout}binding = {binding}) ")?
                    }
                    None => {
                        log::debug!("unassigned binding for {:?}", global.name);
                        if let crate::AddressSpace::Storage { .. } = global.space {
                            if self.options.version.supports_std430_layout() {
                                write!(self.out, "layout(std430) ")?
                            }
                        }
                    }
                }
            }
        }

        if let crate::AddressSpace::Storage { access } = global.space {
            self.write_storage_access(access)?;
        }

        if let Some(storage_qualifier) = glsl_storage_qualifier(global.space) {
            write!(self.out, "{storage_qualifier} ")?;
        }

        match global.space {
            crate::AddressSpace::Private => {
                self.write_simple_global(handle, global)?;
            }
            crate::AddressSpace::WorkGroup => {
                self.write_simple_global(handle, global)?;
            }
            crate::AddressSpace::PushConstant => {
                self.write_simple_global(handle, global)?;
            }
            crate::AddressSpace::Uniform => {
                self.write_interface_block(handle, global)?;
            }
            crate::AddressSpace::Storage { .. } => {
                self.write_interface_block(handle, global)?;
            }
            // A global variable in the `Function` address space is a
            // contradiction in terms.
            crate::AddressSpace::Function => unreachable!(),
            // Textures and samplers are handled directly in `Writer::write`.
            crate::AddressSpace::Handle => unreachable!(),
        }

        Ok(())
    }

    fn write_simple_global(
        &mut self,
        handle: Handle<crate::GlobalVariable>,
        global: &crate::GlobalVariable,
    ) -> BackendResult {
        self.write_type(global.ty)?;
        write!(self.out, " ")?;
        self.write_global_name(handle, global)?;

        if let TypeInner::Array { base, size, .. } = self.module.types[global.ty].inner {
            self.write_array_size(base, size)?;
        }

        if global.space.initializable() && is_value_init_supported(self.module, global.ty) {
            write!(self.out, " = ")?;
            if let Some(init) = global.init {
                self.write_const_expr(init)?;
            } else {
                self.write_zero_init_value(global.ty)?;
            }
        }

        writeln!(self.out, ";")?;

        if let crate::AddressSpace::PushConstant = global.space {
            let global_name = self.get_global_name(handle, global);
            self.reflection_names_globals.insert(handle, global_name);
        }

        Ok(())
    }

    /// Write an interface block for a single Naga global.
    ///
    /// Write `block_name { members }`. Since `block_name` must be unique
    /// between blocks and structs, we add `_block_ID` where `ID` is a
    /// `IdGenerator` generated number. Write `members` in the same way we write
    /// a struct's members.
    fn write_interface_block(
        &mut self,
        handle: Handle<crate::GlobalVariable>,
        global: &crate::GlobalVariable,
    ) -> BackendResult {
        // Write the block name, it's just the struct name appended with `_block_ID`
        let ty_name = &self.names[&NameKey::Type(global.ty)];
        let block_name = format!(
            "{}_block_{}{:?}",
            // avoid double underscores as they are reserved in GLSL
            ty_name.trim_end_matches('_'),
            self.block_id.generate(),
            self.entry_point.stage,
        );
        write!(self.out, "{block_name} ")?;
        self.reflection_names_globals.insert(handle, block_name);

        match self.module.types[global.ty].inner {
            crate::TypeInner::Struct { ref members, .. }
                if self.module.types[members.last().unwrap().ty]
                    .inner
                    .is_dynamically_sized(&self.module.types) =>
            {
                // Structs with dynamically sized arrays must have their
                // members lifted up as members of the interface block. GLSL
                // can't write such struct types anyway.
                self.write_struct_body(global.ty, members)?;
                write!(self.out, " ")?;
                self.write_global_name(handle, global)?;
            }
            _ => {
                // A global of any other type is written as the sole member
                // of the interface block. Since the interface block is
                // anonymous, this becomes visible in the global scope.
                write!(self.out, "{{ ")?;
                self.write_type(global.ty)?;
                write!(self.out, " ")?;
                self.write_global_name(handle, global)?;
                if let TypeInner::Array { base, size, .. } = self.module.types[global.ty].inner {
                    self.write_array_size(base, size)?;
                }
                write!(self.out, "; }}")?;
            }
        }

        writeln!(self.out, ";")?;

        Ok(())
    }

    /// Helper method used to find which expressions of a given function require baking
    ///
    /// # Notes
    /// Clears `need_bake_expressions` set before adding to it
    fn update_expressions_to_bake(&mut self, func: &crate::Function, info: &valid::FunctionInfo) {
        use crate::Expression;
        self.need_bake_expressions.clear();
        for (fun_handle, expr) in func.expressions.iter() {
            let expr_info = &info[fun_handle];
            let min_ref_count = func.expressions[fun_handle].bake_ref_count();
            if min_ref_count <= expr_info.ref_count {
                self.need_bake_expressions.insert(fun_handle);
            }

            let inner = expr_info.ty.inner_with(&self.module.types);

            if let Expression::Math { fun, arg, arg1, .. } = *expr {
                match fun {
                    crate::MathFunction::Dot => {
                        // if the expression is a Dot product with integer arguments,
                        // then the args needs baking as well
                        if let TypeInner::Scalar { kind, .. } = *inner {
                            match kind {
                                crate::ScalarKind::Sint | crate::ScalarKind::Uint => {
                                    self.need_bake_expressions.insert(arg);
                                    self.need_bake_expressions.insert(arg1.unwrap());
                                }
                                _ => {}
                            }
                        }
                    }
                    crate::MathFunction::CountLeadingZeros => {
                        if let Some(crate::ScalarKind::Sint) = inner.scalar_kind() {
                            self.need_bake_expressions.insert(arg);
                        }
                    }
                    _ => {}
                }
            }
        }
    }

    /// Helper method used to get a name for a global
    ///
    /// Globals have different naming schemes depending on their binding:
    /// - Globals without bindings use the name from the [`Namer`](crate::proc::Namer)
    /// - Globals with resource binding are named `_group_X_binding_Y` where `X`
    ///   is the group and `Y` is the binding
    fn get_global_name(
        &self,
        handle: Handle<crate::GlobalVariable>,
        global: &crate::GlobalVariable,
    ) -> String {
        match global.binding {
            Some(ref br) => {
                format!(
                    "_group_{}_binding_{}_{}",
                    br.group,
                    br.binding,
                    self.entry_point.stage.to_str()
                )
            }
            None => self.names[&NameKey::GlobalVariable(handle)].clone(),
        }
    }

    /// Helper method used to write a name for a global without additional heap allocation
    fn write_global_name(
        &mut self,
        handle: Handle<crate::GlobalVariable>,
        global: &crate::GlobalVariable,
    ) -> BackendResult {
        match global.binding {
            Some(ref br) => write!(
                self.out,
                "_group_{}_binding_{}_{}",
                br.group,
                br.binding,
                self.entry_point.stage.to_str()
            )?,
            None => write!(
                self.out,
                "{}",
                &self.names[&NameKey::GlobalVariable(handle)]
            )?,
        }

        Ok(())
    }

    /// Write a GLSL global that will carry a Naga entry point's argument or return value.
    ///
    /// A Naga entry point's arguments and return value are rendered in GLSL as
    /// variables at global scope with the `in` and `out` storage qualifiers.
    /// The code we generate for `main` loads from all the `in` globals into
    /// appropriately named locals. Before it returns, `main` assigns the
    /// components of its return value into all the `out` globals.
    ///
    /// This function writes a declaration for one such GLSL global,
    /// representing a value passed into or returned from [`self.entry_point`]
    /// that has a [`Location`] binding. The global's name is generated based on
    /// the location index and the shader stages being connected; see
    /// [`VaryingName`]. This means we don't need to know the names of
    /// arguments, just their types and bindings.
    ///
    /// Emit nothing for entry point arguments or return values with [`BuiltIn`]
    /// bindings; `main` will read from or assign to the appropriate GLSL
    /// special variable; these are pre-declared. As an exception, we do declare
    /// `gl_Position` or `gl_FragCoord` with the `invariant` qualifier if
    /// needed.
    ///
    /// Use `output` together with [`self.entry_point.stage`] to determine which
    /// shader stages are being connected, and choose the `in` or `out` storage
    /// qualifier.
    ///
    /// [`self.entry_point`]: Writer::entry_point
    /// [`self.entry_point.stage`]: crate::EntryPoint::stage
    /// [`Location`]: crate::Binding::Location
    /// [`BuiltIn`]: crate::Binding::BuiltIn
    fn write_varying(
        &mut self,
        binding: Option<&crate::Binding>,
        ty: Handle<crate::Type>,
        output: bool,
    ) -> Result<(), Error> {
        // For a struct, emit a separate global for each member with a binding.
        if let crate::TypeInner::Struct { ref members, .. } = self.module.types[ty].inner {
            for member in members {
                self.write_varying(member.binding.as_ref(), member.ty, output)?;
            }
            return Ok(());
        }

        let binding = match binding {
            None => return Ok(()),
            Some(binding) => binding,
        };

        let (location, interpolation, sampling, second_blend_source) = match *binding {
            crate::Binding::Location {
                location,
                interpolation,
                sampling,
                second_blend_source,
            } => (location, interpolation, sampling, second_blend_source),
            crate::Binding::BuiltIn(built_in) => {
                if let crate::BuiltIn::Position { invariant: true } = built_in {
                    match (self.options.version, self.entry_point.stage) {
                        (
                            Version::Embedded {
                                version: 300,
                                is_webgl: true,
                            },
                            ShaderStage::Fragment,
                        ) => {
                            // `invariant gl_FragCoord` is not allowed in WebGL2 and possibly
                            // OpenGL ES in general (waiting on confirmation).
                            //
                            // See https://github.com/KhronosGroup/WebGL/issues/3518
                        }
                        _ => {
                            writeln!(
                                self.out,
                                "invariant {};",
                                glsl_built_in(built_in, output, self.options.version.is_webgl())
                            )?;
                        }
                    }
                }
                return Ok(());
            }
        };

        // Write the interpolation modifier if needed
        //
        // We ignore all interpolation and auxiliary modifiers that aren't used in fragment
        // shaders' input globals or vertex shaders' output globals.
        let emit_interpolation_and_auxiliary = match self.entry_point.stage {
            ShaderStage::Vertex => output,
            ShaderStage::Fragment => !output,
            ShaderStage::Compute => false,
        };

        // Write the I/O locations, if allowed
        if self.options.version.supports_explicit_locations() || !emit_interpolation_and_auxiliary {
            if second_blend_source {
                write!(self.out, "layout(location = {location}, index = 1) ")?;
            } else {
                write!(self.out, "layout(location = {location}) ")?;
            }
        }

        // Write the interpolation qualifier.
        if let Some(interp) = interpolation {
            if emit_interpolation_and_auxiliary {
                write!(self.out, "{} ", glsl_interpolation(interp))?;
            }
        }

        // Write the sampling auxiliary qualifier.
        //
        // Before GLSL 4.2, the `centroid` and `sample` qualifiers were required to appear
        // immediately before the `in` / `out` qualifier, so we'll just follow that rule
        // here, regardless of the version.
        if let Some(sampling) = sampling {
            if emit_interpolation_and_auxiliary {
                if let Some(qualifier) = glsl_sampling(sampling) {
                    write!(self.out, "{qualifier} ")?;
                }
            }
        }

        // Write the input/output qualifier.
        write!(self.out, "{} ", if output { "out" } else { "in" })?;

        // Write the type
        // `write_type` adds no leading or trailing spaces
        self.write_type(ty)?;

        // Finally write the global name and end the global with a `;` and a newline
        // Leading space is important
        let vname = VaryingName {
            binding: &crate::Binding::Location {
                location,
                interpolation: None,
                sampling: None,
                second_blend_source,
            },
            stage: self.entry_point.stage,
            output,
            targetting_webgl: self.options.version.is_webgl(),
        };
        writeln!(self.out, " {vname};")?;

        Ok(())
    }

    /// Helper method used to write functions (both entry points and regular functions)
    ///
    /// # Notes
    /// Adds a newline
    fn write_function(
        &mut self,
        ty: back::FunctionType,
        func: &crate::Function,
        info: &valid::FunctionInfo,
    ) -> BackendResult {
        // Create a function context for the function being written
        let ctx = back::FunctionCtx {
            ty,
            info,
            expressions: &func.expressions,
            named_expressions: &func.named_expressions,
        };

        self.named_expressions.clear();
        self.update_expressions_to_bake(func, info);

        // Write the function header
        //
        // glsl headers are the same as in c:
        // `ret_type name(args)`
        // `ret_type` is the return type
        // `name` is the function name
        // `args` is a comma separated list of `type name`
        //  | - `type` is the argument type
        //  | - `name` is the argument name

        // Start by writing the return type if any otherwise write void
        // This is the only place where `void` is a valid type
        // (though it's more a keyword than a type)
        if let back::FunctionType::EntryPoint(_) = ctx.ty {
            write!(self.out, "void")?;
        } else if let Some(ref result) = func.result {
            self.write_type(result.ty)?;
            if let TypeInner::Array { base, size, .. } = self.module.types[result.ty].inner {
                self.write_array_size(base, size)?
            }
        } else {
            write!(self.out, "void")?;
        }

        // Write the function name and open parentheses for the argument list
        let function_name = match ctx.ty {
            back::FunctionType::Function(handle) => &self.names[&NameKey::Function(handle)],
            back::FunctionType::EntryPoint(_) => "main",
        };
        write!(self.out, " {function_name}(")?;

        // Write the comma separated argument list
        //
        // We need access to `Self` here so we use the reference passed to the closure as an
        // argument instead of capturing as that would cause a borrow checker error
        let arguments = match ctx.ty {
            back::FunctionType::EntryPoint(_) => &[][..],
            back::FunctionType::Function(_) => &func.arguments,
        };
        let arguments: Vec<_> = arguments
            .iter()
            .enumerate()
            .filter(|&(_, arg)| match self.module.types[arg.ty].inner {
                TypeInner::Sampler { .. } => false,
                _ => true,
            })
            .collect();
        self.write_slice(&arguments, |this, _, &(i, arg)| {
            // Write the argument type
            match this.module.types[arg.ty].inner {
                // We treat images separately because they might require
                // writing the storage format
                TypeInner::Image {
                    dim,
                    arrayed,
                    class,
                } => {
                    // Write the storage format if needed
                    if let TypeInner::Image {
                        class: crate::ImageClass::Storage { format, .. },
                        ..
                    } = this.module.types[arg.ty].inner
                    {
                        write!(this.out, "layout({}) ", glsl_storage_format(format)?)?;
                    }

                    // write the type
                    //
                    // This is way we need the leading space because `write_image_type` doesn't add
                    // any spaces at the beginning or end
                    this.write_image_type(dim, arrayed, class)?;
                }
                TypeInner::Pointer { base, .. } => {
                    // write parameter qualifiers
                    write!(this.out, "inout ")?;
                    this.write_type(base)?;
                }
                // All other types are written by `write_type`
                _ => {
                    this.write_type(arg.ty)?;
                }
            }

            // Write the argument name
            // The leading space is important
            write!(this.out, " {}", &this.names[&ctx.argument_key(i as u32)])?;

            // Write array size
            match this.module.types[arg.ty].inner {
                TypeInner::Array { base, size, .. } => {
                    this.write_array_size(base, size)?;
                }
                TypeInner::Pointer { base, .. } => {
                    if let TypeInner::Array { base, size, .. } = this.module.types[base].inner {
                        this.write_array_size(base, size)?;
                    }
                }
                _ => {}
            }

            Ok(())
        })?;

        // Close the parentheses and open braces to start the function body
        writeln!(self.out, ") {{")?;

        if self.options.zero_initialize_workgroup_memory
            && ctx.ty.is_compute_entry_point(self.module)
        {
            self.write_workgroup_variables_initialization(&ctx)?;
        }

        // Compose the function arguments from globals, in case of an entry point.
        if let back::FunctionType::EntryPoint(ep_index) = ctx.ty {
            let stage = self.module.entry_points[ep_index as usize].stage;
            for (index, arg) in func.arguments.iter().enumerate() {
                write!(self.out, "{}", back::INDENT)?;
                self.write_type(arg.ty)?;
                let name = &self.names[&NameKey::EntryPointArgument(ep_index, index as u32)];
                write!(self.out, " {name}")?;
                write!(self.out, " = ")?;
                match self.module.types[arg.ty].inner {
                    crate::TypeInner::Struct { ref members, .. } => {
                        self.write_type(arg.ty)?;
                        write!(self.out, "(")?;
                        for (index, member) in members.iter().enumerate() {
                            let varying_name = VaryingName {
                                binding: member.binding.as_ref().unwrap(),
                                stage,
                                output: false,
                                targetting_webgl: self.options.version.is_webgl(),
                            };
                            if index != 0 {
                                write!(self.out, ", ")?;
                            }
                            write!(self.out, "{varying_name}")?;
                        }
                        writeln!(self.out, ");")?;
                    }
                    _ => {
                        let varying_name = VaryingName {
                            binding: arg.binding.as_ref().unwrap(),
                            stage,
                            output: false,
                            targetting_webgl: self.options.version.is_webgl(),
                        };
                        writeln!(self.out, "{varying_name};")?;
                    }
                }
            }
        }

        // Write all function locals
        // Locals are `type name (= init)?;` where the init part (including the =) are optional
        //
        // Always adds a newline
        for (handle, local) in func.local_variables.iter() {
            // Write indentation (only for readability) and the type
            // `write_type` adds no trailing space
            write!(self.out, "{}", back::INDENT)?;
            self.write_type(local.ty)?;

            // Write the local name
            // The leading space is important
            write!(self.out, " {}", self.names[&ctx.name_key(handle)])?;
            // Write size for array type
            if let TypeInner::Array { base, size, .. } = self.module.types[local.ty].inner {
                self.write_array_size(base, size)?;
            }
            // Write the local initializer if needed
            if let Some(init) = local.init {
                // Put the equal signal only if there's a initializer
                // The leading and trailing spaces aren't needed but help with readability
                write!(self.out, " = ")?;

                // Write the constant
                // `write_constant` adds no trailing or leading space/newline
                self.write_expr(init, &ctx)?;
            } else if is_value_init_supported(self.module, local.ty) {
                write!(self.out, " = ")?;
                self.write_zero_init_value(local.ty)?;
            }

            // Finish the local with `;` and add a newline (only for readability)
            writeln!(self.out, ";")?
        }

        // Write the function body (statement list)
        for sta in func.body.iter() {
            // Write a statement, the indentation should always be 1 when writing the function body
            // `write_stmt` adds a newline
            self.write_stmt(sta, &ctx, back::Level(1))?;
        }

        // Close braces and add a newline
        writeln!(self.out, "}}")?;

        Ok(())
    }

    fn write_workgroup_variables_initialization(
        &mut self,
        ctx: &back::FunctionCtx,
    ) -> BackendResult {
        let mut vars = self
            .module
            .global_variables
            .iter()
            .filter(|&(handle, var)| {
                !ctx.info[handle].is_empty() && var.space == crate::AddressSpace::WorkGroup
            })
            .peekable();

        if vars.peek().is_some() {
            let level = back::Level(1);

            writeln!(self.out, "{level}if (gl_LocalInvocationID == uvec3(0u)) {{")?;

            for (handle, var) in vars {
                let name = &self.names[&NameKey::GlobalVariable(handle)];
                write!(self.out, "{}{} = ", level.next(), name)?;
                self.write_zero_init_value(var.ty)?;
                writeln!(self.out, ";")?;
            }

            writeln!(self.out, "{level}}}")?;
            self.write_barrier(crate::Barrier::WORK_GROUP, level)?;
        }

        Ok(())
    }

    /// Write a list of comma separated `T` values using a writer function `F`.
    ///
    /// The writer function `F` receives a mutable reference to `self` that if needed won't cause
    /// borrow checker issues (using for example a closure with `self` will cause issues), the
    /// second argument is the 0 based index of the element on the list, and the last element is
    /// a reference to the element `T` being written
    ///
    /// # Notes
    /// - Adds no newlines or leading/trailing whitespace
    /// - The last element won't have a trailing `,`
    fn write_slice<T, F: FnMut(&mut Self, u32, &T) -> BackendResult>(
        &mut self,
        data: &[T],
        mut f: F,
    ) -> BackendResult {
        // Loop through `data` invoking `f` for each element
        for (index, item) in data.iter().enumerate() {
            if index != 0 {
                write!(self.out, ", ")?;
            }
            f(self, index as u32, item)?;
        }

        Ok(())
    }

    /// Helper method used to write global constants
    fn write_global_constant(&mut self, handle: Handle<crate::Constant>) -> BackendResult {
        write!(self.out, "const ")?;
        let constant = &self.module.constants[handle];
        self.write_type(constant.ty)?;
        let name = &self.names[&NameKey::Constant(handle)];
        write!(self.out, " {name}")?;
        if let TypeInner::Array { base, size, .. } = self.module.types[constant.ty].inner {
            self.write_array_size(base, size)?;
        }
        write!(self.out, " = ")?;
        self.write_const_expr(constant.init)?;
        writeln!(self.out, ";")?;
        Ok(())
    }

    /// Helper method used to output a dot product as an arithmetic expression
    ///
    fn write_dot_product(
        &mut self,
        arg: Handle<crate::Expression>,
        arg1: Handle<crate::Expression>,
        size: usize,
        ctx: &back::FunctionCtx,
    ) -> BackendResult {
        // Write parantheses around the dot product expression to prevent operators
        // with different precedences from applying earlier.
        write!(self.out, "(")?;

        // Cycle trough all the components of the vector
        for index in 0..size {
            let component = back::COMPONENTS[index];
            // Write the addition to the previous product
            // This will print an extra '+' at the beginning but that is fine in glsl
            write!(self.out, " + ")?;
            // Write the first vector expression, this expression is marked to be
            // cached so unless it can't be cached (for example, it's a Constant)
            // it shouldn't produce large expressions.
            self.write_expr(arg, ctx)?;
            // Access the current component on the first vector
            write!(self.out, ".{component} * ")?;
            // Write the second vector expression, this expression is marked to be
            // cached so unless it can't be cached (for example, it's a Constant)
            // it shouldn't produce large expressions.
            self.write_expr(arg1, ctx)?;
            // Access the current component on the second vector
            write!(self.out, ".{component}")?;
        }

        write!(self.out, ")")?;
        Ok(())
    }

    /// Helper method used to write structs
    ///
    /// # Notes
    /// Ends in a newline
    fn write_struct_body(
        &mut self,
        handle: Handle<crate::Type>,
        members: &[crate::StructMember],
    ) -> BackendResult {
        // glsl structs are written as in C
        // `struct name() { members };`
        //  | `struct` is a keyword
        //  | `name` is the struct name
        //  | `members` is a semicolon separated list of `type name`
        //      | `type` is the member type
        //      | `name` is the member name
        writeln!(self.out, "{{")?;

        for (idx, member) in members.iter().enumerate() {
            // The indentation is only for readability
            write!(self.out, "{}", back::INDENT)?;

            match self.module.types[member.ty].inner {
                TypeInner::Array {
                    base,
                    size,
                    stride: _,
                } => {
                    self.write_type(base)?;
                    write!(
                        self.out,
                        " {}",
                        &self.names[&NameKey::StructMember(handle, idx as u32)]
                    )?;
                    // Write [size]
                    self.write_array_size(base, size)?;
                    // Newline is important
                    writeln!(self.out, ";")?;
                }
                _ => {
                    // Write the member type
                    // Adds no trailing space
                    self.write_type(member.ty)?;

                    // Write the member name and put a semicolon
                    // The leading space is important
                    // All members must have a semicolon even the last one
                    writeln!(
                        self.out,
                        " {};",
                        &self.names[&NameKey::StructMember(handle, idx as u32)]
                    )?;
                }
            }
        }

        write!(self.out, "}}")?;
        Ok(())
    }

    /// Helper method used to write statements
    ///
    /// # Notes
    /// Always adds a newline
    fn write_stmt(
        &mut self,
        sta: &crate::Statement,
        ctx: &back::FunctionCtx,
        level: back::Level,
    ) -> BackendResult {
        use crate::Statement;

        match *sta {
            // This is where we can generate intermediate constants for some expression types.
            Statement::Emit(ref range) => {
                for handle in range.clone() {
                    let info = &ctx.info[handle];
                    let ptr_class = info.ty.inner_with(&self.module.types).pointer_space();
                    let expr_name = if ptr_class.is_some() {
                        // GLSL can't save a pointer-valued expression in a variable,
                        // but we shouldn't ever need to: they should never be named expressions,
                        // and none of the expression types flagged by bake_ref_count can be pointer-valued.
                        None
                    } else if let Some(name) = ctx.named_expressions.get(&handle) {
                        // Front end provides names for all variables at the start of writing.
                        // But we write them to step by step. We need to recache them
                        // Otherwise, we could accidentally write variable name instead of full expression.
                        // Also, we use sanitized names! It defense backend from generating variable with name from reserved keywords.
                        Some(self.namer.call(name))
                    } else if self.need_bake_expressions.contains(&handle) {
                        Some(format!("{}{}", back::BAKE_PREFIX, handle.index()))
                    } else {
                        None
                    };

                    // If we are going to write an `ImageLoad` next and the target image
                    // is sampled and we are using the `Restrict` policy for bounds
                    // checking images we need to write a local holding the clamped lod.
                    if let crate::Expression::ImageLoad {
                        image,
                        level: Some(level_expr),
                        ..
                    } = ctx.expressions[handle]
                    {
                        if let TypeInner::Image {
                            class: crate::ImageClass::Sampled { .. },
                            ..
                        } = *ctx.info[image].ty.inner_with(&self.module.types)
                        {
                            if let proc::BoundsCheckPolicy::Restrict = self.policies.image_load {
                                write!(self.out, "{level}")?;
                                self.write_clamped_lod(ctx, handle, image, level_expr)?
                            }
                        }
                    }

                    if let Some(name) = expr_name {
                        write!(self.out, "{level}")?;
                        self.write_named_expr(handle, name, handle, ctx)?;
                    }
                }
            }
            // Blocks are simple we just need to write the block statements between braces
            // We could also just print the statements but this is more readable and maps more
            // closely to the IR
            Statement::Block(ref block) => {
                write!(self.out, "{level}")?;
                writeln!(self.out, "{{")?;
                for sta in block.iter() {
                    // Increase the indentation to help with readability
                    self.write_stmt(sta, ctx, level.next())?
                }
                writeln!(self.out, "{level}}}")?
            }
            // Ifs are written as in C:
            // ```
            // if(condition) {
            //  accept
            // } else {
            //  reject
            // }
            // ```
            Statement::If {
                condition,
                ref accept,
                ref reject,
            } => {
                write!(self.out, "{level}")?;
                write!(self.out, "if (")?;
                self.write_expr(condition, ctx)?;
                writeln!(self.out, ") {{")?;

                for sta in accept {
                    // Increase indentation to help with readability
                    self.write_stmt(sta, ctx, level.next())?;
                }

                // If there are no statements in the reject block we skip writing it
                // This is only for readability
                if !reject.is_empty() {
                    writeln!(self.out, "{level}}} else {{")?;

                    for sta in reject {
                        // Increase indentation to help with readability
                        self.write_stmt(sta, ctx, level.next())?;
                    }
                }

                writeln!(self.out, "{level}}}")?
            }
            // Switch are written as in C:
            // ```
            // switch (selector) {
            //      // Fallthrough
            //      case label:
            //          block
            //      // Non fallthrough
            //      case label:
            //          block
            //          break;
            //      default:
            //          block
            //  }
            //  ```
            //  Where the `default` case happens isn't important but we put it last
            //  so that we don't need to print a `break` for it
            Statement::Switch {
                selector,
                ref cases,
            } => {
                // Start the switch
                write!(self.out, "{level}")?;
                write!(self.out, "switch(")?;
                self.write_expr(selector, ctx)?;
                writeln!(self.out, ") {{")?;

                // Write all cases
                let l2 = level.next();
                for case in cases {
                    match case.value {
                        crate::SwitchValue::I32(value) => write!(self.out, "{l2}case {value}:")?,
                        crate::SwitchValue::U32(value) => write!(self.out, "{l2}case {value}u:")?,
                        crate::SwitchValue::Default => write!(self.out, "{l2}default:")?,
                    }

                    let write_block_braces = !(case.fall_through && case.body.is_empty());
                    if write_block_braces {
                        writeln!(self.out, " {{")?;
                    } else {
                        writeln!(self.out)?;
                    }

                    for sta in case.body.iter() {
                        self.write_stmt(sta, ctx, l2.next())?;
                    }

                    if !case.fall_through && case.body.last().map_or(true, |s| !s.is_terminator()) {
                        writeln!(self.out, "{}break;", l2.next())?;
                    }

                    if write_block_braces {
                        writeln!(self.out, "{l2}}}")?;
                    }
                }

                writeln!(self.out, "{level}}}")?
            }
            // Loops in naga IR are based on wgsl loops, glsl can emulate the behaviour by using a
            // while true loop and appending the continuing block to the body resulting on:
            // ```
            // bool loop_init = true;
            // while(true) {
            //  if (!loop_init) { <continuing> }
            //  loop_init = false;
            //  <body>
            // }
            // ```
            Statement::Loop {
                ref body,
                ref continuing,
                break_if,
            } => {
                if !continuing.is_empty() || break_if.is_some() {
                    let gate_name = self.namer.call("loop_init");
                    writeln!(self.out, "{level}bool {gate_name} = true;")?;
                    writeln!(self.out, "{level}while(true) {{")?;
                    let l2 = level.next();
                    let l3 = l2.next();
                    writeln!(self.out, "{l2}if (!{gate_name}) {{")?;
                    for sta in continuing {
                        self.write_stmt(sta, ctx, l3)?;
                    }
                    if let Some(condition) = break_if {
                        write!(self.out, "{l3}if (")?;
                        self.write_expr(condition, ctx)?;
                        writeln!(self.out, ") {{")?;
                        writeln!(self.out, "{}break;", l3.next())?;
                        writeln!(self.out, "{l3}}}")?;
                    }
                    writeln!(self.out, "{l2}}}")?;
                    writeln!(self.out, "{}{} = false;", level.next(), gate_name)?;
                } else {
                    writeln!(self.out, "{level}while(true) {{")?;
                }
                for sta in body {
                    self.write_stmt(sta, ctx, level.next())?;
                }
                writeln!(self.out, "{level}}}")?
            }
            // Break, continue and return as written as in C
            // `break;`
            Statement::Break => {
                write!(self.out, "{level}")?;
                writeln!(self.out, "break;")?
            }
            // `continue;`
            Statement::Continue => {
                write!(self.out, "{level}")?;
                writeln!(self.out, "continue;")?
            }
            // `return expr;`, `expr` is optional
            Statement::Return { value } => {
                write!(self.out, "{level}")?;
                match ctx.ty {
                    back::FunctionType::Function(_) => {
                        write!(self.out, "return")?;
                        // Write the expression to be returned if needed
                        if let Some(expr) = value {
                            write!(self.out, " ")?;
                            self.write_expr(expr, ctx)?;
                        }
                        writeln!(self.out, ";")?;
                    }
                    back::FunctionType::EntryPoint(ep_index) => {
                        let mut has_point_size = false;
                        let ep = &self.module.entry_points[ep_index as usize];
                        if let Some(ref result) = ep.function.result {
                            let value = value.unwrap();
                            match self.module.types[result.ty].inner {
                                crate::TypeInner::Struct { ref members, .. } => {
                                    let temp_struct_name = match ctx.expressions[value] {
                                        crate::Expression::Compose { .. } => {
                                            let return_struct = "_tmp_return";
                                            write!(
                                                self.out,
                                                "{} {} = ",
                                                &self.names[&NameKey::Type(result.ty)],
                                                return_struct
                                            )?;
                                            self.write_expr(value, ctx)?;
                                            writeln!(self.out, ";")?;
                                            write!(self.out, "{level}")?;
                                            Some(return_struct)
                                        }
                                        _ => None,
                                    };

                                    for (index, member) in members.iter().enumerate() {
                                        if let Some(crate::Binding::BuiltIn(
                                            crate::BuiltIn::PointSize,
                                        )) = member.binding
                                        {
                                            has_point_size = true;
                                        }

                                        let varying_name = VaryingName {
                                            binding: member.binding.as_ref().unwrap(),
                                            stage: ep.stage,
                                            output: true,
                                            targetting_webgl: self.options.version.is_webgl(),
                                        };
                                        write!(self.out, "{varying_name} = ")?;

                                        if let Some(struct_name) = temp_struct_name {
                                            write!(self.out, "{struct_name}")?;
                                        } else {
                                            self.write_expr(value, ctx)?;
                                        }

                                        // Write field name
                                        writeln!(
                                            self.out,
                                            ".{};",
                                            &self.names
                                                [&NameKey::StructMember(result.ty, index as u32)]
                                        )?;
                                        write!(self.out, "{level}")?;
                                    }
                                }
                                _ => {
                                    let name = VaryingName {
                                        binding: result.binding.as_ref().unwrap(),
                                        stage: ep.stage,
                                        output: true,
                                        targetting_webgl: self.options.version.is_webgl(),
                                    };
                                    write!(self.out, "{name} = ")?;
                                    self.write_expr(value, ctx)?;
                                    writeln!(self.out, ";")?;
                                    write!(self.out, "{level}")?;
                                }
                            }
                        }

                        let is_vertex_stage = self.module.entry_points[ep_index as usize].stage
                            == ShaderStage::Vertex;
                        if is_vertex_stage
                            && self
                                .options
                                .writer_flags
                                .contains(WriterFlags::ADJUST_COORDINATE_SPACE)
                        {
                            writeln!(
                                self.out,
                                "gl_Position.yz = vec2(-gl_Position.y, gl_Position.z * 2.0 - gl_Position.w);",
                            )?;
                            write!(self.out, "{level}")?;
                        }

                        if is_vertex_stage
                            && self
                                .options
                                .writer_flags
                                .contains(WriterFlags::FORCE_POINT_SIZE)
                            && !has_point_size
                        {
                            writeln!(self.out, "gl_PointSize = 1.0;")?;
                            write!(self.out, "{level}")?;
                        }
                        writeln!(self.out, "return;")?;
                    }
                }
            }
            // This is one of the places were glsl adds to the syntax of C in this case the discard
            // keyword which ceases all further processing in a fragment shader, it's called OpKill
            // in spir-v that's why it's called `Statement::Kill`
            Statement::Kill => writeln!(self.out, "{level}discard;")?,
            Statement::Barrier(flags) => {
                self.write_barrier(flags, level)?;
            }
            // Stores in glsl are just variable assignments written as `pointer = value;`
            Statement::Store { pointer, value } => {
                write!(self.out, "{level}")?;
                self.write_expr(pointer, ctx)?;
                write!(self.out, " = ")?;
                self.write_expr(value, ctx)?;
                writeln!(self.out, ";")?
            }
            Statement::WorkGroupUniformLoad { pointer, result } => {
                // GLSL doesn't have pointers, which means that this backend needs to ensure that
                // the actual "loading" is happening between the two barriers.
                // This is done in `Emit` by never emitting a variable name for pointer variables
                self.write_barrier(crate::Barrier::WORK_GROUP, level)?;

                let result_name = format!("{}{}", back::BAKE_PREFIX, result.index());
                write!(self.out, "{level}")?;
                // Expressions cannot have side effects, so just writing the expression here is fine.
                self.write_named_expr(pointer, result_name, result, ctx)?;

                self.write_barrier(crate::Barrier::WORK_GROUP, level)?;
            }
            // Stores a value into an image.
            Statement::ImageStore {
                image,
                coordinate,
                array_index,
                value,
            } => {
                write!(self.out, "{level}")?;
                self.write_image_store(ctx, image, coordinate, array_index, value)?
            }
            // A `Call` is written `name(arguments)` where `arguments` is a comma separated expressions list
            Statement::Call {
                function,
                ref arguments,
                result,
            } => {
                write!(self.out, "{level}")?;
                if let Some(expr) = result {
                    let name = format!("{}{}", back::BAKE_PREFIX, expr.index());
                    let result = self.module.functions[function].result.as_ref().unwrap();
                    self.write_type(result.ty)?;
                    write!(self.out, " {name}")?;
                    if let TypeInner::Array { base, size, .. } = self.module.types[result.ty].inner
                    {
                        self.write_array_size(base, size)?
                    }
                    write!(self.out, " = ")?;
                    self.named_expressions.insert(expr, name);
                }
                write!(self.out, "{}(", &self.names[&NameKey::Function(function)])?;
                let arguments: Vec<_> = arguments
                    .iter()
                    .enumerate()
                    .filter_map(|(i, arg)| {
                        let arg_ty = self.module.functions[function].arguments[i].ty;
                        match self.module.types[arg_ty].inner {
                            TypeInner::Sampler { .. } => None,
                            _ => Some(*arg),
                        }
                    })
                    .collect();
                self.write_slice(&arguments, |this, _, arg| this.write_expr(*arg, ctx))?;
                writeln!(self.out, ");")?
            }
            Statement::Atomic {
                pointer,
                ref fun,
                value,
                result,
            } => {
                write!(self.out, "{level}")?;
                let res_name = format!("{}{}", back::BAKE_PREFIX, result.index());
                let res_ty = ctx.info[result].ty.inner_with(&self.module.types);
                self.write_value_type(res_ty)?;
                write!(self.out, " {res_name} = ")?;
                self.named_expressions.insert(result, res_name);

                let fun_str = fun.to_glsl();
                write!(self.out, "atomic{fun_str}(")?;
                self.write_expr(pointer, ctx)?;
                write!(self.out, ", ")?;
                // handle the special cases
                match *fun {
                    crate::AtomicFunction::Subtract => {
                        // we just wrote `InterlockedAdd`, so negate the argument
                        write!(self.out, "-")?;
                    }
                    crate::AtomicFunction::Exchange { compare: Some(_) } => {
                        return Err(Error::Custom(
                            "atomic CompareExchange is not implemented".to_string(),
                        ));
                    }
                    _ => {}
                }
                self.write_expr(value, ctx)?;
                writeln!(self.out, ");")?;
            }
            Statement::RayQuery { .. } => unreachable!(),
        }

        Ok(())
    }

    /// Write a const expression.
    ///
    /// Write `expr`, a handle to an [`Expression`] in the current [`Module`]'s
    /// constant expression arena, as GLSL expression.
    ///
    /// # Notes
    /// Adds no newlines or leading/trailing whitespace
    ///
    /// [`Expression`]: crate::Expression
    /// [`Module`]: crate::Module
    fn write_const_expr(&mut self, expr: Handle<crate::Expression>) -> BackendResult {
        self.write_possibly_const_expr(
            expr,
            &self.module.const_expressions,
            |expr| &self.info[expr],
            |writer, expr| writer.write_const_expr(expr),
        )
    }

    /// Write [`Expression`] variants that can occur in both runtime and const expressions.
    ///
    /// Write `expr`, a handle to an [`Expression`] in the arena `expressions`,
    /// as as GLSL expression. This must be one of the [`Expression`] variants
    /// that is allowed to occur in constant expressions.
    ///
    /// Use `write_expression` to write subexpressions.
    ///
    /// This is the common code for `write_expr`, which handles arbitrary
    /// runtime expressions, and `write_const_expr`, which only handles
    /// const-expressions. Each of those callers passes itself (essentially) as
    /// the `write_expression` callback, so that subexpressions are restricted
    /// to the appropriate variants.
    ///
    /// # Notes
    /// Adds no newlines or leading/trailing whitespace
    ///
    /// [`Expression`]: crate::Expression
    fn write_possibly_const_expr<'w, I, E>(
        &'w mut self,
        expr: Handle<crate::Expression>,
        expressions: &crate::Arena<crate::Expression>,
        info: I,
        write_expression: E,
    ) -> BackendResult
    where
        I: Fn(Handle<crate::Expression>) -> &'w proc::TypeResolution,
        E: Fn(&mut Self, Handle<crate::Expression>) -> BackendResult,
    {
        use crate::Expression;

        match expressions[expr] {
            Expression::Literal(literal) => {
                match literal {
                    // Floats are written using `Debug` instead of `Display` because it always appends the
                    // decimal part even it's zero which is needed for a valid glsl float constant
                    crate::Literal::F64(value) => write!(self.out, "{:?}LF", value)?,
                    crate::Literal::F32(value) => write!(self.out, "{:?}", value)?,
                    // Unsigned integers need a `u` at the end
                    //
                    // While `core` doesn't necessarily need it, it's allowed and since `es` needs it we
                    // always write it as the extra branch wouldn't have any benefit in readability
                    crate::Literal::U32(value) => write!(self.out, "{}u", value)?,
                    crate::Literal::I32(value) => write!(self.out, "{}", value)?,
                    crate::Literal::Bool(value) => write!(self.out, "{}", value)?,
                }
            }
            Expression::Constant(handle) => {
                let constant = &self.module.constants[handle];
                if constant.name.is_some() {
                    write!(self.out, "{}", self.names[&NameKey::Constant(handle)])?;
                } else {
                    self.write_const_expr(constant.init)?;
                }
            }
            Expression::ZeroValue(ty) => {
                self.write_zero_init_value(ty)?;
            }
            Expression::Compose { ty, ref components } => {
                self.write_type(ty)?;

                if let TypeInner::Array { base, size, .. } = self.module.types[ty].inner {
                    self.write_array_size(base, size)?;
                }

                write!(self.out, "(")?;
                for (index, component) in components.iter().enumerate() {
                    if index != 0 {
                        write!(self.out, ", ")?;
                    }
                    write_expression(self, *component)?;
                }
                write!(self.out, ")")?
            }
            // `Splat` needs to actually write down a vector, it's not always inferred in GLSL.
            Expression::Splat { size: _, value } => {
                let resolved = info(expr).inner_with(&self.module.types);
                self.write_value_type(resolved)?;
                write!(self.out, "(")?;
                write_expression(self, value)?;
                write!(self.out, ")")?
            }
            _ => unreachable!(),
        }

        Ok(())
    }

    /// Helper method to write expressions
    ///
    /// # Notes
    /// Doesn't add any newlines or leading/trailing spaces
    fn write_expr(
        &mut self,
        expr: Handle<crate::Expression>,
        ctx: &back::FunctionCtx,
    ) -> BackendResult {
        use crate::Expression;

        if let Some(name) = self.named_expressions.get(&expr) {
            write!(self.out, "{name}")?;
            return Ok(());
        }

        match ctx.expressions[expr] {
            Expression::Literal(_)
            | Expression::Constant(_)
            | Expression::ZeroValue(_)
            | Expression::Compose { .. }
            | Expression::Splat { .. } => {
                self.write_possibly_const_expr(
                    expr,
                    ctx.expressions,
                    |expr| &ctx.info[expr].ty,
                    |writer, expr| writer.write_expr(expr, ctx),
                )?;
            }
            // `Access` is applied to arrays, vectors and matrices and is written as indexing
            Expression::Access { base, index } => {
                self.write_expr(base, ctx)?;
                write!(self.out, "[")?;
                self.write_expr(index, ctx)?;
                write!(self.out, "]")?
            }
            // `AccessIndex` is the same as `Access` except that the index is a constant and it can
            // be applied to structs, in this case we need to find the name of the field at that
            // index and write `base.field_name`
            Expression::AccessIndex { base, index } => {
                self.write_expr(base, ctx)?;

                let base_ty_res = &ctx.info[base].ty;
                let mut resolved = base_ty_res.inner_with(&self.module.types);
                let base_ty_handle = match *resolved {
                    TypeInner::Pointer { base, space: _ } => {
                        resolved = &self.module.types[base].inner;
                        Some(base)
                    }
                    _ => base_ty_res.handle(),
                };

                match *resolved {
                    TypeInner::Vector { .. } => {
                        // Write vector access as a swizzle
                        write!(self.out, ".{}", back::COMPONENTS[index as usize])?
                    }
                    TypeInner::Matrix { .. }
                    | TypeInner::Array { .. }
                    | TypeInner::ValuePointer { .. } => write!(self.out, "[{index}]")?,
                    TypeInner::Struct { .. } => {
                        // This will never panic in case the type is a `Struct`, this is not true
                        // for other types so we can only check while inside this match arm
                        let ty = base_ty_handle.unwrap();

                        write!(
                            self.out,
                            ".{}",
                            &self.names[&NameKey::StructMember(ty, index)]
                        )?
                    }
                    ref other => return Err(Error::Custom(format!("Cannot index {other:?}"))),
                }
            }
            // `Swizzle` adds a few letters behind the dot.
            Expression::Swizzle {
                size,
                vector,
                pattern,
            } => {
                self.write_expr(vector, ctx)?;
                write!(self.out, ".")?;
                for &sc in pattern[..size as usize].iter() {
                    self.out.write_char(back::COMPONENTS[sc as usize])?;
                }
            }
            // Function arguments are written as the argument name
            Expression::FunctionArgument(pos) => {
                write!(self.out, "{}", &self.names[&ctx.argument_key(pos)])?
            }
            // Global variables need some special work for their name but
            // `get_global_name` does the work for us
            Expression::GlobalVariable(handle) => {
                let global = &self.module.global_variables[handle];
                self.write_global_name(handle, global)?
            }
            // A local is written as it's name
            Expression::LocalVariable(handle) => {
                write!(self.out, "{}", self.names[&ctx.name_key(handle)])?
            }
            // glsl has no pointers so there's no load operation, just write the pointer expression
            Expression::Load { pointer } => self.write_expr(pointer, ctx)?,
            // `ImageSample` is a bit complicated compared to the rest of the IR.
            //
            // First there are three variations depending whether the sample level is explicitly set,
            // if it's automatic or it it's bias:
            // `texture(image, coordinate)` - Automatic sample level
            // `texture(image, coordinate, bias)` - Bias sample level
            // `textureLod(image, coordinate, level)` - Zero or Exact sample level
            //
            // Furthermore if `depth_ref` is some we need to append it to the coordinate vector
            Expression::ImageSample {
                image,
                sampler: _, //TODO?
                gather,
                coordinate,
                array_index,
                offset,
                level,
                depth_ref,
            } => {
                let dim = match *ctx.info[image].ty.inner_with(&self.module.types) {
                    TypeInner::Image { dim, .. } => dim,
                    _ => unreachable!(),
                };

                if dim == crate::ImageDimension::Cube
                    && array_index.is_some()
                    && depth_ref.is_some()
                {
                    match level {
                        crate::SampleLevel::Zero
                        | crate::SampleLevel::Exact(_)
                        | crate::SampleLevel::Gradient { .. }
                        | crate::SampleLevel::Bias(_) => {
                            return Err(Error::Custom(String::from(
                                "gsamplerCubeArrayShadow isn't supported in textureGrad, \
                                 textureLod or texture with bias",
                            )))
                        }
                        crate::SampleLevel::Auto => {}
                    }
                }

                // textureLod on sampler2DArrayShadow and samplerCubeShadow does not exist in GLSL.
                // To emulate this, we will have to use textureGrad with a constant gradient of 0.
                let workaround_lod_array_shadow_as_grad = (array_index.is_some()
                    || dim == crate::ImageDimension::Cube)
                    && depth_ref.is_some()
                    && gather.is_none()
                    && !self
                        .options
                        .writer_flags
                        .contains(WriterFlags::TEXTURE_SHADOW_LOD);

                //Write the function to be used depending on the sample level
                let fun_name = match level {
                    crate::SampleLevel::Zero if gather.is_some() => "textureGather",
                    crate::SampleLevel::Auto | crate::SampleLevel::Bias(_) => "texture",
                    crate::SampleLevel::Zero | crate::SampleLevel::Exact(_) => {
                        if workaround_lod_array_shadow_as_grad {
                            "textureGrad"
                        } else {
                            "textureLod"
                        }
                    }
                    crate::SampleLevel::Gradient { .. } => "textureGrad",
                };
                let offset_name = match offset {
                    Some(_) => "Offset",
                    None => "",
                };

                write!(self.out, "{fun_name}{offset_name}(")?;

                // Write the image that will be used
                self.write_expr(image, ctx)?;
                // The space here isn't required but it helps with readability
                write!(self.out, ", ")?;

                // We need to get the coordinates vector size to later build a vector that's `size + 1`
                // if `depth_ref` is some, if it isn't a vector we panic as that's not a valid expression
                let mut coord_dim = match *ctx.info[coordinate].ty.inner_with(&self.module.types) {
                    TypeInner::Vector { size, .. } => size as u8,
                    TypeInner::Scalar { .. } => 1,
                    _ => unreachable!(),
                };

                if array_index.is_some() {
                    coord_dim += 1;
                }
                let merge_depth_ref = depth_ref.is_some() && gather.is_none() && coord_dim < 4;
                if merge_depth_ref {
                    coord_dim += 1;
                }

                let tex_1d_hack = dim == crate::ImageDimension::D1 && self.options.version.is_es();
                let is_vec = tex_1d_hack || coord_dim != 1;
                // Compose a new texture coordinates vector
                if is_vec {
                    write!(self.out, "vec{}(", coord_dim + tex_1d_hack as u8)?;
                }
                self.write_expr(coordinate, ctx)?;
                if tex_1d_hack {
                    write!(self.out, ", 0.0")?;
                }
                if let Some(expr) = array_index {
                    write!(self.out, ", ")?;
                    self.write_expr(expr, ctx)?;
                }
                if merge_depth_ref {
                    write!(self.out, ", ")?;
                    self.write_expr(depth_ref.unwrap(), ctx)?;
                }
                if is_vec {
                    write!(self.out, ")")?;
                }

                if let (Some(expr), false) = (depth_ref, merge_depth_ref) {
                    write!(self.out, ", ")?;
                    self.write_expr(expr, ctx)?;
                }

                match level {
                    // Auto needs no more arguments
                    crate::SampleLevel::Auto => (),
                    // Zero needs level set to 0
                    crate::SampleLevel::Zero => {
                        if workaround_lod_array_shadow_as_grad {
                            let vec_dim = match dim {
                                crate::ImageDimension::Cube => 3,
                                _ => 2,
                            };
                            write!(self.out, ", vec{vec_dim}(0.0), vec{vec_dim}(0.0)")?;
                        } else if gather.is_none() {
                            write!(self.out, ", 0.0")?;
                        }
                    }
                    // Exact and bias require another argument
                    crate::SampleLevel::Exact(expr) => {
                        if workaround_lod_array_shadow_as_grad {
                            log::warn!("Unable to `textureLod` a shadow array, ignoring the LOD");
                            write!(self.out, ", vec2(0,0), vec2(0,0)")?;
                        } else {
                            write!(self.out, ", ")?;
                            self.write_expr(expr, ctx)?;
                        }
                    }
                    crate::SampleLevel::Bias(_) => {
                        // This needs to be done after the offset writing
                    }
                    crate::SampleLevel::Gradient { x, y } => {
                        // If we are using sampler2D to replace sampler1D, we also
                        // need to make sure to use vec2 gradients
                        if tex_1d_hack {
                            write!(self.out, ", vec2(")?;
                            self.write_expr(x, ctx)?;
                            write!(self.out, ", 0.0)")?;
                            write!(self.out, ", vec2(")?;
                            self.write_expr(y, ctx)?;
                            write!(self.out, ", 0.0)")?;
                        } else {
                            write!(self.out, ", ")?;
                            self.write_expr(x, ctx)?;
                            write!(self.out, ", ")?;
                            self.write_expr(y, ctx)?;
                        }
                    }
                }

                if let Some(constant) = offset {
                    write!(self.out, ", ")?;
                    if tex_1d_hack {
                        write!(self.out, "ivec2(")?;
                    }
                    self.write_const_expr(constant)?;
                    if tex_1d_hack {
                        write!(self.out, ", 0)")?;
                    }
                }

                // Bias is always the last argument
                if let crate::SampleLevel::Bias(expr) = level {
                    write!(self.out, ", ")?;
                    self.write_expr(expr, ctx)?;
                }

                if let (Some(component), None) = (gather, depth_ref) {
                    write!(self.out, ", {}", component as usize)?;
                }

                // End the function
                write!(self.out, ")")?
            }
            Expression::ImageLoad {
                image,
                coordinate,
                array_index,
                sample,
                level,
            } => self.write_image_load(expr, ctx, image, coordinate, array_index, sample, level)?,
            // Query translates into one of the:
            // - textureSize/imageSize
            // - textureQueryLevels
            // - textureSamples/imageSamples
            Expression::ImageQuery { image, query } => {
                use crate::ImageClass;

                // This will only panic if the module is invalid
                let (dim, class) = match *ctx.info[image].ty.inner_with(&self.module.types) {
                    TypeInner::Image {
                        dim,
                        arrayed: _,
                        class,
                    } => (dim, class),
                    _ => unreachable!(),
                };
                let components = match dim {
                    crate::ImageDimension::D1 => 1,
                    crate::ImageDimension::D2 => 2,
                    crate::ImageDimension::D3 => 3,
                    crate::ImageDimension::Cube => 2,
                };

                if let crate::ImageQuery::Size { .. } = query {
                    match components {
                        1 => write!(self.out, "uint(")?,
                        _ => write!(self.out, "uvec{components}(")?,
                    }
                } else {
                    write!(self.out, "uint(")?;
                }

                match query {
                    crate::ImageQuery::Size { level } => {
                        match class {
                            ImageClass::Sampled { multi, .. } | ImageClass::Depth { multi } => {
                                write!(self.out, "textureSize(")?;
                                self.write_expr(image, ctx)?;
                                if let Some(expr) = level {
                                    let cast_to_int = matches!(
                                        *ctx.info[expr].ty.inner_with(&self.module.types),
                                        crate::TypeInner::Scalar {
                                            kind: crate::ScalarKind::Uint,
                                            ..
                                        }
                                    );

                                    write!(self.out, ", ")?;

                                    if cast_to_int {
                                        write!(self.out, "int(")?;
                                    }

                                    self.write_expr(expr, ctx)?;

                                    if cast_to_int {
                                        write!(self.out, ")")?;
                                    }
                                } else if !multi {
                                    // All textureSize calls requires an lod argument
                                    // except for multisampled samplers
                                    write!(self.out, ", 0")?;
                                }
                            }
                            ImageClass::Storage { .. } => {
                                write!(self.out, "imageSize(")?;
                                self.write_expr(image, ctx)?;
                            }
                        }
                        write!(self.out, ")")?;
                        if components != 1 || self.options.version.is_es() {
                            write!(self.out, ".{}", &"xyz"[..components])?;
                        }
                    }
                    crate::ImageQuery::NumLevels => {
                        write!(self.out, "textureQueryLevels(",)?;
                        self.write_expr(image, ctx)?;
                        write!(self.out, ")",)?;
                    }
                    crate::ImageQuery::NumLayers => {
                        let fun_name = match class {
                            ImageClass::Sampled { .. } | ImageClass::Depth { .. } => "textureSize",
                            ImageClass::Storage { .. } => "imageSize",
                        };
                        write!(self.out, "{fun_name}(")?;
                        self.write_expr(image, ctx)?;
                        // All textureSize calls requires an lod argument
                        // except for multisampled samplers
                        if class.is_multisampled() {
                            write!(self.out, ", 0")?;
                        }
                        write!(self.out, ")")?;
                        if components != 1 || self.options.version.is_es() {
                            write!(self.out, ".{}", back::COMPONENTS[components])?;
                        }
                    }
                    crate::ImageQuery::NumSamples => {
                        let fun_name = match class {
                            ImageClass::Sampled { .. } | ImageClass::Depth { .. } => {
                                "textureSamples"
                            }
                            ImageClass::Storage { .. } => "imageSamples",
                        };
                        write!(self.out, "{fun_name}(")?;
                        self.write_expr(image, ctx)?;
                        write!(self.out, ")",)?;
                    }
                }

                write!(self.out, ")")?;
            }
            // `Unary` is pretty straightforward
            // "-" - for `Negate`
            // "~" - for `Not` if it's an integer
            // "!" - for `Not` if it's a boolean
            //
            // We also wrap the everything in parentheses to avoid precedence issues
            Expression::Unary { op, expr } => {
                use crate::{ScalarKind as Sk, UnaryOperator as Uo};

                let ty = ctx.info[expr].ty.inner_with(&self.module.types);

                match *ty {
                    TypeInner::Vector { kind: Sk::Bool, .. } => {
                        write!(self.out, "not(")?;
                    }
                    _ => {
                        let operator = match op {
                            Uo::Negate => "-",
                            Uo::Not => match ty.scalar_kind() {
                                Some(Sk::Sint) | Some(Sk::Uint) => "~",
                                Some(Sk::Bool) => "!",
                                ref other => {
                                    return Err(Error::Custom(format!(
                                        "Cannot apply not to type {other:?}"
                                    )))
                                }
                            },
                        };

                        write!(self.out, "{operator}(")?;
                    }
                }

                self.write_expr(expr, ctx)?;

                write!(self.out, ")")?
            }
            // `Binary` we just write `left op right`, except when dealing with
            // comparison operations on vectors as they are implemented with
            // builtin functions.
            // Once again we wrap everything in parentheses to avoid precedence issues
            Expression::Binary {
                mut op,
                left,
                right,
            } => {
                // Holds `Some(function_name)` if the binary operation is
                // implemented as a function call
                use crate::{BinaryOperator as Bo, ScalarKind as Sk, TypeInner as Ti};

                let left_inner = ctx.info[left].ty.inner_with(&self.module.types);
                let right_inner = ctx.info[right].ty.inner_with(&self.module.types);

                let function = match (left_inner, right_inner) {
                    (&Ti::Vector { kind, .. }, &Ti::Vector { .. }) => match op {
                        Bo::Less
                        | Bo::LessEqual
                        | Bo::Greater
                        | Bo::GreaterEqual
                        | Bo::Equal
                        | Bo::NotEqual => BinaryOperation::VectorCompare,
                        Bo::Modulo if kind == Sk::Float => BinaryOperation::Modulo,
                        Bo::And if kind == Sk::Bool => {
                            op = crate::BinaryOperator::LogicalAnd;
                            BinaryOperation::VectorComponentWise
                        }
                        Bo::InclusiveOr if kind == Sk::Bool => {
                            op = crate::BinaryOperator::LogicalOr;
                            BinaryOperation::VectorComponentWise
                        }
                        _ => BinaryOperation::Other,
                    },
                    _ => match (left_inner.scalar_kind(), right_inner.scalar_kind()) {
                        (Some(Sk::Float), _) | (_, Some(Sk::Float)) => match op {
                            Bo::Modulo => BinaryOperation::Modulo,
                            _ => BinaryOperation::Other,
                        },
                        (Some(Sk::Bool), Some(Sk::Bool)) => match op {
                            Bo::InclusiveOr => {
                                op = crate::BinaryOperator::LogicalOr;
                                BinaryOperation::Other
                            }
                            Bo::And => {
                                op = crate::BinaryOperator::LogicalAnd;
                                BinaryOperation::Other
                            }
                            _ => BinaryOperation::Other,
                        },
                        _ => BinaryOperation::Other,
                    },
                };

                match function {
                    BinaryOperation::VectorCompare => {
                        let op_str = match op {
                            Bo::Less => "lessThan(",
                            Bo::LessEqual => "lessThanEqual(",
                            Bo::Greater => "greaterThan(",
                            Bo::GreaterEqual => "greaterThanEqual(",
                            Bo::Equal => "equal(",
                            Bo::NotEqual => "notEqual(",
                            _ => unreachable!(),
                        };
                        write!(self.out, "{op_str}")?;
                        self.write_expr(left, ctx)?;
                        write!(self.out, ", ")?;
                        self.write_expr(right, ctx)?;
                        write!(self.out, ")")?;
                    }
                    BinaryOperation::VectorComponentWise => {
                        self.write_value_type(left_inner)?;
                        write!(self.out, "(")?;

                        let size = match *left_inner {
                            Ti::Vector { size, .. } => size,
                            _ => unreachable!(),
                        };

                        for i in 0..size as usize {
                            if i != 0 {
                                write!(self.out, ", ")?;
                            }

                            self.write_expr(left, ctx)?;
                            write!(self.out, ".{}", back::COMPONENTS[i])?;

                            write!(self.out, " {} ", back::binary_operation_str(op))?;

                            self.write_expr(right, ctx)?;
                            write!(self.out, ".{}", back::COMPONENTS[i])?;
                        }

                        write!(self.out, ")")?;
                    }
                    // TODO: handle undefined behavior of BinaryOperator::Modulo
                    //
                    // sint:
                    // if right == 0 return 0
                    // if left == min(type_of(left)) && right == -1 return 0
                    // if sign(left) == -1 || sign(right) == -1 return result as defined by WGSL
                    //
                    // uint:
                    // if right == 0 return 0
                    //
                    // float:
                    // if right == 0 return ? see https://github.com/gpuweb/gpuweb/issues/2798
                    BinaryOperation::Modulo => {
                        write!(self.out, "(")?;

                        // write `e1 - e2 * trunc(e1 / e2)`
                        self.write_expr(left, ctx)?;
                        write!(self.out, " - ")?;
                        self.write_expr(right, ctx)?;
                        write!(self.out, " * ")?;
                        write!(self.out, "trunc(")?;
                        self.write_expr(left, ctx)?;
                        write!(self.out, " / ")?;
                        self.write_expr(right, ctx)?;
                        write!(self.out, ")")?;

                        write!(self.out, ")")?;
                    }
                    BinaryOperation::Other => {
                        write!(self.out, "(")?;

                        self.write_expr(left, ctx)?;
                        write!(self.out, " {} ", back::binary_operation_str(op))?;
                        self.write_expr(right, ctx)?;

                        write!(self.out, ")")?;
                    }
                }
            }
            // `Select` is written as `condition ? accept : reject`
            // We wrap everything in parentheses to avoid precedence issues
            Expression::Select {
                condition,
                accept,
                reject,
            } => {
                let cond_ty = ctx.info[condition].ty.inner_with(&self.module.types);
                let vec_select = if let TypeInner::Vector { .. } = *cond_ty {
                    true
                } else {
                    false
                };

                // TODO: Boolean mix on desktop required GL_EXT_shader_integer_mix
                if vec_select {
                    // Glsl defines that for mix when the condition is a boolean the first element
                    // is picked if condition is false and the second if condition is true
                    write!(self.out, "mix(")?;
                    self.write_expr(reject, ctx)?;
                    write!(self.out, ", ")?;
                    self.write_expr(accept, ctx)?;
                    write!(self.out, ", ")?;
                    self.write_expr(condition, ctx)?;
                } else {
                    write!(self.out, "(")?;
                    self.write_expr(condition, ctx)?;
                    write!(self.out, " ? ")?;
                    self.write_expr(accept, ctx)?;
                    write!(self.out, " : ")?;
                    self.write_expr(reject, ctx)?;
                }

                write!(self.out, ")")?
            }
            // `Derivative` is a function call to a glsl provided function
            Expression::Derivative { axis, ctrl, expr } => {
                use crate::{DerivativeAxis as Axis, DerivativeControl as Ctrl};
                let fun_name = if self.options.version.supports_derivative_control() {
                    match (axis, ctrl) {
                        (Axis::X, Ctrl::Coarse) => "dFdxCoarse",
                        (Axis::X, Ctrl::Fine) => "dFdxFine",
                        (Axis::X, Ctrl::None) => "dFdx",
                        (Axis::Y, Ctrl::Coarse) => "dFdyCoarse",
                        (Axis::Y, Ctrl::Fine) => "dFdyFine",
                        (Axis::Y, Ctrl::None) => "dFdy",
                        (Axis::Width, Ctrl::Coarse) => "fwidthCoarse",
                        (Axis::Width, Ctrl::Fine) => "fwidthFine",
                        (Axis::Width, Ctrl::None) => "fwidth",
                    }
                } else {
                    match axis {
                        Axis::X => "dFdx",
                        Axis::Y => "dFdy",
                        Axis::Width => "fwidth",
                    }
                };
                write!(self.out, "{fun_name}(")?;
                self.write_expr(expr, ctx)?;
                write!(self.out, ")")?
            }
            // `Relational` is a normal function call to some glsl provided functions
            Expression::Relational { fun, argument } => {
                use crate::RelationalFunction as Rf;

                let fun_name = match fun {
                    // There's no specific function for this but we can invert the result of `isinf`
                    Rf::IsFinite => "!isinf",
                    Rf::IsInf => "isinf",
                    Rf::IsNan => "isnan",
                    // There's also no function for this but we can invert `isnan`
                    Rf::IsNormal => "!isnan",
                    Rf::All => "all",
                    Rf::Any => "any",
                };
                write!(self.out, "{fun_name}(")?;

                self.write_expr(argument, ctx)?;

                write!(self.out, ")")?
            }
            Expression::Math {
                fun,
                arg,
                arg1,
                arg2,
                arg3,
            } => {
                use crate::MathFunction as Mf;

                let fun_name = match fun {
                    // comparison
                    Mf::Abs => "abs",
                    Mf::Min => "min",
                    Mf::Max => "max",
                    Mf::Clamp => "clamp",
                    Mf::Saturate => {
                        write!(self.out, "clamp(")?;

                        self.write_expr(arg, ctx)?;

                        match *ctx.info[arg].ty.inner_with(&self.module.types) {
                            crate::TypeInner::Vector { size, .. } => write!(
                                self.out,
                                ", vec{}(0.0), vec{0}(1.0)",
                                back::vector_size_str(size)
                            )?,
                            _ => write!(self.out, ", 0.0, 1.0")?,
                        }

                        write!(self.out, ")")?;

                        return Ok(());
                    }
                    // trigonometry
                    Mf::Cos => "cos",
                    Mf::Cosh => "cosh",
                    Mf::Sin => "sin",
                    Mf::Sinh => "sinh",
                    Mf::Tan => "tan",
                    Mf::Tanh => "tanh",
                    Mf::Acos => "acos",
                    Mf::Asin => "asin",
                    Mf::Atan => "atan",
                    Mf::Asinh => "asinh",
                    Mf::Acosh => "acosh",
                    Mf::Atanh => "atanh",
                    Mf::Radians => "radians",
                    Mf::Degrees => "degrees",
                    // glsl doesn't have atan2 function
                    // use two-argument variation of the atan function
                    Mf::Atan2 => "atan",
                    // decomposition
                    Mf::Ceil => "ceil",
                    Mf::Floor => "floor",
                    Mf::Round => "roundEven",
                    Mf::Fract => "fract",
                    Mf::Trunc => "trunc",
                    Mf::Modf => MODF_FUNCTION,
                    Mf::Frexp => FREXP_FUNCTION,
                    Mf::Ldexp => "ldexp",
                    // exponent
                    Mf::Exp => "exp",
                    Mf::Exp2 => "exp2",
                    Mf::Log => "log",
                    Mf::Log2 => "log2",
                    Mf::Pow => "pow",
                    // geometry
                    Mf::Dot => match *ctx.info[arg].ty.inner_with(&self.module.types) {
                        crate::TypeInner::Vector {
                            kind: crate::ScalarKind::Float,
                            ..
                        } => "dot",
                        crate::TypeInner::Vector { size, .. } => {
                            return self.write_dot_product(arg, arg1.unwrap(), size as usize, ctx)
                        }
                        _ => unreachable!(
                            "Correct TypeInner for dot product should be already validated"
                        ),
                    },
                    Mf::Outer => "outerProduct",
                    Mf::Cross => "cross",
                    Mf::Distance => "distance",
                    Mf::Length => "length",
                    Mf::Normalize => "normalize",
                    Mf::FaceForward => "faceforward",
                    Mf::Reflect => "reflect",
                    Mf::Refract => "refract",
                    // computational
                    Mf::Sign => "sign",
                    Mf::Fma => {
                        if self.options.version.supports_fma_function() {
                            // Use the fma function when available
                            "fma"
                        } else {
                            // No fma support. Transform the function call into an arithmetic expression
                            write!(self.out, "(")?;

                            self.write_expr(arg, ctx)?;
                            write!(self.out, " * ")?;

                            let arg1 =
                                arg1.ok_or_else(|| Error::Custom("Missing fma arg1".to_owned()))?;
                            self.write_expr(arg1, ctx)?;
                            write!(self.out, " + ")?;

                            let arg2 =
                                arg2.ok_or_else(|| Error::Custom("Missing fma arg2".to_owned()))?;
                            self.write_expr(arg2, ctx)?;
                            write!(self.out, ")")?;

                            return Ok(());
                        }
                    }
                    Mf::Mix => "mix",
                    Mf::Step => "step",
                    Mf::SmoothStep => "smoothstep",
                    Mf::Sqrt => "sqrt",
                    Mf::InverseSqrt => "inversesqrt",
                    Mf::Inverse => "inverse",
                    Mf::Transpose => "transpose",
                    Mf::Determinant => "determinant",
                    // bits
                    Mf::CountTrailingZeros => {
                        match *ctx.info[arg].ty.inner_with(&self.module.types) {
                            crate::TypeInner::Vector { size, kind, .. } => {
                                let s = back::vector_size_str(size);
                                if let crate::ScalarKind::Uint = kind {
                                    write!(self.out, "min(uvec{s}(findLSB(")?;
                                    self.write_expr(arg, ctx)?;
                                    write!(self.out, ")), uvec{s}(32u))")?;
                                } else {
                                    write!(self.out, "ivec{s}(min(uvec{s}(findLSB(")?;
                                    self.write_expr(arg, ctx)?;
                                    write!(self.out, ")), uvec{s}(32u)))")?;
                                }
                            }
                            crate::TypeInner::Scalar { kind, .. } => {
                                if let crate::ScalarKind::Uint = kind {
                                    write!(self.out, "min(uint(findLSB(")?;
                                    self.write_expr(arg, ctx)?;
                                    write!(self.out, ")), 32u)")?;
                                } else {
                                    write!(self.out, "int(min(uint(findLSB(")?;
                                    self.write_expr(arg, ctx)?;
                                    write!(self.out, ")), 32u))")?;
                                }
                            }
                            _ => unreachable!(),
                        };
                        return Ok(());
                    }
                    Mf::CountLeadingZeros => {
                        if self.options.version.supports_integer_functions() {
                            match *ctx.info[arg].ty.inner_with(&self.module.types) {
                                crate::TypeInner::Vector { size, kind, .. } => {
                                    let s = back::vector_size_str(size);

                                    if let crate::ScalarKind::Uint = kind {
                                        write!(self.out, "uvec{s}(ivec{s}(31) - findMSB(")?;
                                        self.write_expr(arg, ctx)?;
                                        write!(self.out, "))")?;
                                    } else {
                                        write!(self.out, "mix(ivec{s}(31) - findMSB(")?;
                                        self.write_expr(arg, ctx)?;
                                        write!(self.out, "), ivec{s}(0), lessThan(")?;
                                        self.write_expr(arg, ctx)?;
                                        write!(self.out, ", ivec{s}(0)))")?;
                                    }
                                }
                                crate::TypeInner::Scalar { kind, .. } => {
                                    if let crate::ScalarKind::Uint = kind {
                                        write!(self.out, "uint(31 - findMSB(")?;
                                    } else {
                                        write!(self.out, "(")?;
                                        self.write_expr(arg, ctx)?;
                                        write!(self.out, " < 0 ? 0 : 31 - findMSB(")?;
                                    }

                                    self.write_expr(arg, ctx)?;
                                    write!(self.out, "))")?;
                                }
                                _ => unreachable!(),
                            };
                        } else {
                            match *ctx.info[arg].ty.inner_with(&self.module.types) {
                                crate::TypeInner::Vector { size, kind, .. } => {
                                    let s = back::vector_size_str(size);

                                    if let crate::ScalarKind::Uint = kind {
                                        write!(self.out, "uvec{s}(")?;
                                        write!(self.out, "vec{s}(31.0) - floor(log2(vec{s}(")?;
                                        self.write_expr(arg, ctx)?;
                                        write!(self.out, ") + 0.5)))")?;
                                    } else {
                                        write!(self.out, "ivec{s}(")?;
                                        write!(self.out, "mix(vec{s}(31.0) - floor(log2(vec{s}(")?;
                                        self.write_expr(arg, ctx)?;
                                        write!(self.out, ") + 0.5)), ")?;
                                        write!(self.out, "vec{s}(0.0), lessThan(")?;
                                        self.write_expr(arg, ctx)?;
                                        write!(self.out, ", ivec{s}(0u))))")?;
                                    }
                                }
                                crate::TypeInner::Scalar { kind, .. } => {
                                    if let crate::ScalarKind::Uint = kind {
                                        write!(self.out, "uint(31.0 - floor(log2(float(")?;
                                        self.write_expr(arg, ctx)?;
                                        write!(self.out, ") + 0.5)))")?;
                                    } else {
                                        write!(self.out, "(")?;
                                        self.write_expr(arg, ctx)?;
                                        write!(self.out, " < 0 ? 0 : int(")?;
                                        write!(self.out, "31.0 - floor(log2(float(")?;
                                        self.write_expr(arg, ctx)?;
                                        write!(self.out, ") + 0.5))))")?;
                                    }
                                }
                                _ => unreachable!(),
                            };
                        }

                        return Ok(());
                    }
                    Mf::CountOneBits => "bitCount",
                    Mf::ReverseBits => "bitfieldReverse",
                    Mf::ExtractBits => "bitfieldExtract",
                    Mf::InsertBits => "bitfieldInsert",
                    Mf::FindLsb => "findLSB",
                    Mf::FindMsb => "findMSB",
                    // data packing
                    Mf::Pack4x8snorm => "packSnorm4x8",
                    Mf::Pack4x8unorm => "packUnorm4x8",
                    Mf::Pack2x16snorm => "packSnorm2x16",
                    Mf::Pack2x16unorm => "packUnorm2x16",
                    Mf::Pack2x16float => "packHalf2x16",
                    // data unpacking
                    Mf::Unpack4x8snorm => "unpackSnorm4x8",
                    Mf::Unpack4x8unorm => "unpackUnorm4x8",
                    Mf::Unpack2x16snorm => "unpackSnorm2x16",
                    Mf::Unpack2x16unorm => "unpackUnorm2x16",
                    Mf::Unpack2x16float => "unpackHalf2x16",
                };

                let extract_bits = fun == Mf::ExtractBits;
                let insert_bits = fun == Mf::InsertBits;

                // Some GLSL functions always return signed integers (like findMSB),
                // so they need to be cast to uint if the argument is also an uint.
                let ret_might_need_int_to_uint =
                    matches!(fun, Mf::FindLsb | Mf::FindMsb | Mf::CountOneBits | Mf::Abs);

                // Some GLSL functions only accept signed integers (like abs),
                // so they need their argument cast from uint to int.
                let arg_might_need_uint_to_int = matches!(fun, Mf::Abs);

                // Check if the argument is an unsigned integer and return the vector size
                // in case it's a vector
                let maybe_uint_size = match *ctx.info[arg].ty.inner_with(&self.module.types) {
                    crate::TypeInner::Scalar {
                        kind: crate::ScalarKind::Uint,
                        ..
                    } => Some(None),
                    crate::TypeInner::Vector {
                        kind: crate::ScalarKind::Uint,
                        size,
                        ..
                    } => Some(Some(size)),
                    _ => None,
                };

                // Cast to uint if the function needs it
                if ret_might_need_int_to_uint {
                    if let Some(maybe_size) = maybe_uint_size {
                        match maybe_size {
                            Some(size) => write!(self.out, "uvec{}(", size as u8)?,
                            None => write!(self.out, "uint(")?,
                        }
                    }
                }

                write!(self.out, "{fun_name}(")?;

                // Cast to int if the function needs it
                if arg_might_need_uint_to_int {
                    if let Some(maybe_size) = maybe_uint_size {
                        match maybe_size {
                            Some(size) => write!(self.out, "ivec{}(", size as u8)?,
                            None => write!(self.out, "int(")?,
                        }
                    }
                }

                self.write_expr(arg, ctx)?;

                // Close the cast from uint to int
                if arg_might_need_uint_to_int && maybe_uint_size.is_some() {
                    write!(self.out, ")")?
                }

                if let Some(arg) = arg1 {
                    write!(self.out, ", ")?;
                    if extract_bits {
                        write!(self.out, "int(")?;
                        self.write_expr(arg, ctx)?;
                        write!(self.out, ")")?;
                    } else {
                        self.write_expr(arg, ctx)?;
                    }
                }
                if let Some(arg) = arg2 {
                    write!(self.out, ", ")?;
                    if extract_bits || insert_bits {
                        write!(self.out, "int(")?;
                        self.write_expr(arg, ctx)?;
                        write!(self.out, ")")?;
                    } else {
                        self.write_expr(arg, ctx)?;
                    }
                }
                if let Some(arg) = arg3 {
                    write!(self.out, ", ")?;
                    if insert_bits {
                        write!(self.out, "int(")?;
                        self.write_expr(arg, ctx)?;
                        write!(self.out, ")")?;
                    } else {
                        self.write_expr(arg, ctx)?;
                    }
                }
                write!(self.out, ")")?;

                // Close the cast from int to uint
                if ret_might_need_int_to_uint && maybe_uint_size.is_some() {
                    write!(self.out, ")")?
                }
            }
            // `As` is always a call.
            // If `convert` is true the function name is the type
            // Else the function name is one of the glsl provided bitcast functions
            Expression::As {
                expr,
                kind: target_kind,
                convert,
            } => {
                let inner = ctx.info[expr].ty.inner_with(&self.module.types);
                match convert {
                    Some(width) => {
                        // this is similar to `write_type`, but with the target kind
                        let scalar = glsl_scalar(target_kind, width)?;
                        match *inner {
                            TypeInner::Matrix { columns, rows, .. } => write!(
                                self.out,
                                "{}mat{}x{}",
                                scalar.prefix, columns as u8, rows as u8
                            )?,
                            TypeInner::Vector { size, .. } => {
                                write!(self.out, "{}vec{}", scalar.prefix, size as u8)?
                            }
                            _ => write!(self.out, "{}", scalar.full)?,
                        }

                        write!(self.out, "(")?;
                        self.write_expr(expr, ctx)?;
                        write!(self.out, ")")?
                    }
                    None => {
                        use crate::ScalarKind as Sk;

                        let target_vector_type = match *inner {
                            TypeInner::Vector { size, width, .. } => Some(TypeInner::Vector {
                                size,
                                width,
                                kind: target_kind,
                            }),
                            _ => None,
                        };

                        let source_kind = inner.scalar_kind().unwrap();

                        match (source_kind, target_kind, target_vector_type) {
                            // No conversion needed
                            (Sk::Sint, Sk::Sint, _)
                            | (Sk::Uint, Sk::Uint, _)
                            | (Sk::Float, Sk::Float, _)
                            | (Sk::Bool, Sk::Bool, _) => {
                                self.write_expr(expr, ctx)?;
                                return Ok(());
                            }

                            // Cast to/from floats
                            (Sk::Float, Sk::Sint, _) => write!(self.out, "floatBitsToInt")?,
                            (Sk::Float, Sk::Uint, _) => write!(self.out, "floatBitsToUint")?,
                            (Sk::Sint, Sk::Float, _) => write!(self.out, "intBitsToFloat")?,
                            (Sk::Uint, Sk::Float, _) => write!(self.out, "uintBitsToFloat")?,

                            // Cast between vector types
                            (_, _, Some(vector)) => {
                                self.write_value_type(&vector)?;
                            }

                            // There is no way to bitcast between Uint/Sint in glsl. Use constructor conversion
                            (Sk::Uint | Sk::Bool, Sk::Sint, None) => write!(self.out, "int")?,
                            (Sk::Sint | Sk::Bool, Sk::Uint, None) => write!(self.out, "uint")?,
                            (Sk::Bool, Sk::Float, None) => write!(self.out, "float")?,
                            (Sk::Sint | Sk::Uint | Sk::Float, Sk::Bool, None) => {
                                write!(self.out, "bool")?
                            }
                        };

                        write!(self.out, "(")?;
                        self.write_expr(expr, ctx)?;
                        write!(self.out, ")")?;
                    }
                }
            }
            // These expressions never show up in `Emit`.
            Expression::CallResult(_)
            | Expression::AtomicResult { .. }
            | Expression::RayQueryProceedResult
            | Expression::WorkGroupUniformLoadResult { .. } => unreachable!(),
            // `ArrayLength` is written as `expr.length()` and we convert it to a uint
            Expression::ArrayLength(expr) => {
                write!(self.out, "uint(")?;
                self.write_expr(expr, ctx)?;
                write!(self.out, ".length())")?
            }
            // not supported yet
            Expression::RayQueryGetIntersection { .. } => unreachable!(),
        }

        Ok(())
    }

    /// Helper function to write the local holding the clamped lod
    fn write_clamped_lod(
        &mut self,
        ctx: &back::FunctionCtx,
        expr: Handle<crate::Expression>,
        image: Handle<crate::Expression>,
        level_expr: Handle<crate::Expression>,
    ) -> Result<(), Error> {
        // Define our local and start a call to `clamp`
        write!(
            self.out,
            "int {}{}{} = clamp(",
            back::BAKE_PREFIX,
            expr.index(),
            CLAMPED_LOD_SUFFIX
        )?;
        // Write the lod that will be clamped
        self.write_expr(level_expr, ctx)?;
        // Set the min value to 0 and start a call to `textureQueryLevels` to get
        // the maximum value
        write!(self.out, ", 0, textureQueryLevels(")?;
        // Write the target image as an argument to `textureQueryLevels`
        self.write_expr(image, ctx)?;
        // Close the call to `textureQueryLevels` subtract 1 from it since
        // the lod argument is 0 based, close the `clamp` call and end the
        // local declaration statement.
        writeln!(self.out, ") - 1);")?;

        Ok(())
    }

    // Helper method used to retrieve how many elements a coordinate vector
    // for the images operations need.
    fn get_coordinate_vector_size(&self, dim: crate::ImageDimension, arrayed: bool) -> u8 {
        // openGL es doesn't have 1D images so we need workaround it
        let tex_1d_hack = dim == crate::ImageDimension::D1 && self.options.version.is_es();
        // Get how many components the coordinate vector needs for the dimensions only
        let tex_coord_size = match dim {
            crate::ImageDimension::D1 => 1,
            crate::ImageDimension::D2 => 2,
            crate::ImageDimension::D3 => 3,
            crate::ImageDimension::Cube => 2,
        };
        // Calculate the true size of the coordinate vector by adding 1 for arrayed images
        // and another 1 if we need to workaround 1D images by making them 2D
        tex_coord_size + tex_1d_hack as u8 + arrayed as u8
    }

    /// Helper method to write the coordinate vector for image operations
    fn write_texture_coord(
        &mut self,
        ctx: &back::FunctionCtx,
        vector_size: u8,
        coordinate: Handle<crate::Expression>,
        array_index: Option<Handle<crate::Expression>>,
        // Emulate 1D images as 2D for profiles that don't support it (glsl es)
        tex_1d_hack: bool,
    ) -> Result<(), Error> {
        match array_index {
            // If the image needs an array indice we need to add it to the end of our
            // coordinate vector, to do so we will use the `ivec(ivec, scalar)`
            // constructor notation (NOTE: the inner `ivec` can also be a scalar, this
            // is important for 1D arrayed images).
            Some(layer_expr) => {
                write!(self.out, "ivec{vector_size}(")?;
                self.write_expr(coordinate, ctx)?;
                write!(self.out, ", ")?;
                // If we are replacing sampler1D with sampler2D we also need
                // to add another zero to the coordinates vector for the y component
                if tex_1d_hack {
                    write!(self.out, "0, ")?;
                }
                self.write_expr(layer_expr, ctx)?;
                write!(self.out, ")")?;
            }
            // Otherwise write just the expression (and the 1D hack if needed)
            None => {
                let uvec_size = match *ctx.info[coordinate].ty.inner_with(&self.module.types) {
                    TypeInner::Scalar {
                        kind: crate::ScalarKind::Uint,
                        ..
                    } => Some(None),
                    TypeInner::Vector {
                        size,
                        kind: crate::ScalarKind::Uint,
                        ..
                    } => Some(Some(size as u32)),
                    _ => None,
                };
                if tex_1d_hack {
                    write!(self.out, "ivec2(")?;
                } else if uvec_size.is_some() {
                    match uvec_size {
                        Some(None) => write!(self.out, "int(")?,
                        Some(Some(size)) => write!(self.out, "ivec{size}(")?,
                        _ => {}
                    }
                }
                self.write_expr(coordinate, ctx)?;
                if tex_1d_hack {
                    write!(self.out, ", 0)")?;
                } else if uvec_size.is_some() {
                    write!(self.out, ")")?;
                }
            }
        }

        Ok(())
    }

    /// Helper method to write the `ImageStore` statement
    fn write_image_store(
        &mut self,
        ctx: &back::FunctionCtx,
        image: Handle<crate::Expression>,
        coordinate: Handle<crate::Expression>,
        array_index: Option<Handle<crate::Expression>>,
        value: Handle<crate::Expression>,
    ) -> Result<(), Error> {
        use crate::ImageDimension as IDim;

        // NOTE: openGL requires that `imageStore`s have no effets when the texel is invalid
        // so we don't need to generate bounds checks (OpenGL 4.2 Core §3.9.20)

        // This will only panic if the module is invalid
        let dim = match *ctx.info[image].ty.inner_with(&self.module.types) {
            TypeInner::Image { dim, .. } => dim,
            _ => unreachable!(),
        };

        // Begin our call to `imageStore`
        write!(self.out, "imageStore(")?;
        self.write_expr(image, ctx)?;
        // Separate the image argument from the coordinates
        write!(self.out, ", ")?;

        // openGL es doesn't have 1D images so we need workaround it
        let tex_1d_hack = dim == IDim::D1 && self.options.version.is_es();
        // Write the coordinate vector
        self.write_texture_coord(
            ctx,
            // Get the size of the coordinate vector
            self.get_coordinate_vector_size(dim, array_index.is_some()),
            coordinate,
            array_index,
            tex_1d_hack,
        )?;

        // Separate the coordinate from the value to write and write the expression
        // of the value to write.
        write!(self.out, ", ")?;
        self.write_expr(value, ctx)?;
        // End the call to `imageStore` and the statement.
        writeln!(self.out, ");")?;

        Ok(())
    }

    /// Helper method for writing an `ImageLoad` expression.
    #[allow(clippy::too_many_arguments)]
    fn write_image_load(
        &mut self,
        handle: Handle<crate::Expression>,
        ctx: &back::FunctionCtx,
        image: Handle<crate::Expression>,
        coordinate: Handle<crate::Expression>,
        array_index: Option<Handle<crate::Expression>>,
        sample: Option<Handle<crate::Expression>>,
        level: Option<Handle<crate::Expression>>,
    ) -> Result<(), Error> {
        use crate::ImageDimension as IDim;

        // `ImageLoad` is a bit complicated.
        // There are two functions one for sampled
        // images another for storage images, the former uses `texelFetch` and the
        // latter uses `imageLoad`.
        //
        // Furthermore we have `level` which is always `Some` for sampled images
        // and `None` for storage images, so we end up with two functions:
        // - `texelFetch(image, coordinate, level)` for sampled images
        // - `imageLoad(image, coordinate)` for storage images
        //
        // Finally we also have to consider bounds checking, for storage images
        // this is easy since openGL requires that invalid texels always return
        // 0, for sampled images we need to either verify that all arguments are
        // in bounds (`ReadZeroSkipWrite`) or make them a valid texel (`Restrict`).

        // This will only panic if the module is invalid
        let (dim, class) = match *ctx.info[image].ty.inner_with(&self.module.types) {
            TypeInner::Image {
                dim,
                arrayed: _,
                class,
            } => (dim, class),
            _ => unreachable!(),
        };

        // Get the name of the function to be used for the load operation
        // and the policy to be used with it.
        let (fun_name, policy) = match class {
            // Sampled images inherit the policy from the user passed policies
            crate::ImageClass::Sampled { .. } => ("texelFetch", self.policies.image_load),
            crate::ImageClass::Storage { .. } => {
                // OpenGL ES 3.1 mentiones in Chapter "8.22 Texture Image Loads and Stores" that:
                // "Invalid image loads will return a vector where the value of R, G, and B components
                // is 0 and the value of the A component is undefined."
                //
                // OpenGL 4.2 Core mentiones in Chapter "3.9.20 Texture Image Loads and Stores" that:
                // "Invalid image loads will return zero."
                //
                // So, we only inject bounds checks for ES
                let policy = if self.options.version.is_es() {
                    self.policies.image_load
                } else {
                    proc::BoundsCheckPolicy::Unchecked
                };
                ("imageLoad", policy)
            }
            // TODO: Is there even a function for this?
            crate::ImageClass::Depth { multi: _ } => {
                return Err(Error::Custom(
                    "WGSL `textureLoad` from depth textures is not supported in GLSL".to_string(),
                ))
            }
        };

        // openGL es doesn't have 1D images so we need workaround it
        let tex_1d_hack = dim == IDim::D1 && self.options.version.is_es();
        // Get the size of the coordinate vector
        let vector_size = self.get_coordinate_vector_size(dim, array_index.is_some());

        if let proc::BoundsCheckPolicy::ReadZeroSkipWrite = policy {
            // To write the bounds checks for `ReadZeroSkipWrite` we will use a
            // ternary operator since we are in the middle of an expression and
            // need to return a value.
            //
            // NOTE: glsl does short circuit when evaluating logical
            // expressions so we can be sure that after we test a
            // condition it will be true for the next ones

            // Write parantheses around the ternary operator to prevent problems with
            // expressions emitted before or after it having more precedence
            write!(self.out, "(",)?;

            // The lod check needs to precede the size check since we need
            // to use the lod to get the size of the image at that level.
            if let Some(level_expr) = level {
                self.write_expr(level_expr, ctx)?;
                write!(self.out, " < textureQueryLevels(",)?;
                self.write_expr(image, ctx)?;
                // Chain the next check
                write!(self.out, ") && ")?;
            }

            // Check that the sample arguments doesn't exceed the number of samples
            if let Some(sample_expr) = sample {
                self.write_expr(sample_expr, ctx)?;
                write!(self.out, " < textureSamples(",)?;
                self.write_expr(image, ctx)?;
                // Chain the next check
                write!(self.out, ") && ")?;
            }

            // We now need to write the size checks for the coordinates and array index
            // first we write the comparation function in case the image is 1D non arrayed
            // (and no 1D to 2D hack was needed) we are comparing scalars so the less than
            // operator will suffice, but otherwise we'll be comparing two vectors so we'll
            // need to use the `lessThan` function but it returns a vector of booleans (one
            // for each comparison) so we need to fold it all in one scalar boolean, since
            // we want all comparisons to pass we use the `all` function which will only
            // return `true` if all the elements of the boolean vector are also `true`.
            //
            // So we'll end with one of the following forms
            // - `coord < textureSize(image, lod)` for 1D images
            // - `all(lessThan(coord, textureSize(image, lod)))` for normal images
            // - `all(lessThan(ivec(coord, array_index), textureSize(image, lod)))`
            //    for arrayed images
            // - `all(lessThan(coord, textureSize(image)))` for multi sampled images

            if vector_size != 1 {
                write!(self.out, "all(lessThan(")?;
            }

            // Write the coordinate vector
            self.write_texture_coord(ctx, vector_size, coordinate, array_index, tex_1d_hack)?;

            if vector_size != 1 {
                // If we used the `lessThan` function we need to separate the
                // coordinates from the image size.
                write!(self.out, ", ")?;
            } else {
                // If we didn't use it (ie. 1D images) we perform the comparsion
                // using the less than operator.
                write!(self.out, " < ")?;
            }

            // Call `textureSize` to get our image size
            write!(self.out, "textureSize(")?;
            self.write_expr(image, ctx)?;
            // `textureSize` uses the lod as a second argument for mipmapped images
            if let Some(level_expr) = level {
                // Separate the image from the lod
                write!(self.out, ", ")?;
                self.write_expr(level_expr, ctx)?;
            }
            // Close the `textureSize` call
            write!(self.out, ")")?;

            if vector_size != 1 {
                // Close the `all` and `lessThan` calls
                write!(self.out, "))")?;
            }

            // Finally end the condition part of the ternary operator
            write!(self.out, " ? ")?;
        }

        // Begin the call to the function used to load the texel
        write!(self.out, "{fun_name}(")?;
        self.write_expr(image, ctx)?;
        write!(self.out, ", ")?;

        // If we are using `Restrict` bounds checking we need to pass valid texel
        // coordinates, to do so we use the `clamp` function to get a value between
        // 0 and the image size - 1 (indexing begins at 0)
        if let proc::BoundsCheckPolicy::Restrict = policy {
            write!(self.out, "clamp(")?;
        }

        // Write the coordinate vector
        self.write_texture_coord(ctx, vector_size, coordinate, array_index, tex_1d_hack)?;

        // If we are using `Restrict` bounds checking we need to write the rest of the
        // clamp we initiated before writing the coordinates.
        if let proc::BoundsCheckPolicy::Restrict = policy {
            // Write the min value 0
            if vector_size == 1 {
                write!(self.out, ", 0")?;
            } else {
                write!(self.out, ", ivec{vector_size}(0)")?;
            }
            // Start the `textureSize` call to use as the max value.
            write!(self.out, ", textureSize(")?;
            self.write_expr(image, ctx)?;
            // If the image is mipmapped we need to add the lod argument to the
            // `textureSize` call, but this needs to be the clamped lod, this should
            // have been generated earlier and put in a local.
            if class.is_mipmapped() {
                write!(
                    self.out,
                    ", {}{}{}",
                    back::BAKE_PREFIX,
                    handle.index(),
                    CLAMPED_LOD_SUFFIX
                )?;
            }
            // Close the `textureSize` call
            write!(self.out, ")")?;

            // Subtract 1 from the `textureSize` call since the coordinates are zero based.
            if vector_size == 1 {
                write!(self.out, " - 1")?;
            } else {
                write!(self.out, " - ivec{vector_size}(1)")?;
            }

            // Close the `clamp` call
            write!(self.out, ")")?;

            // Add the clamped lod (if present) as the second argument to the
            // image load function.
            if level.is_some() {
                write!(
                    self.out,
                    ", {}{}{}",
                    back::BAKE_PREFIX,
                    handle.index(),
                    CLAMPED_LOD_SUFFIX
                )?;
            }

            // If a sample argument is needed we need to clamp it between 0 and
            // the number of samples the image has.
            if let Some(sample_expr) = sample {
                write!(self.out, ", clamp(")?;
                self.write_expr(sample_expr, ctx)?;
                // Set the min value to 0 and start the call to `textureSamples`
                write!(self.out, ", 0, textureSamples(")?;
                self.write_expr(image, ctx)?;
                // Close the `textureSamples` call, subtract 1 from it since the sample
                // argument is zero based, and close the `clamp` call
                writeln!(self.out, ") - 1)")?;
            }
        } else if let Some(sample_or_level) = sample.or(level) {
            // If no bounds checking is need just add the sample or level argument
            // after the coordinates
            write!(self.out, ", ")?;
            self.write_expr(sample_or_level, ctx)?;
        }

        // Close the image load function.
        write!(self.out, ")")?;

        // If we were using the `ReadZeroSkipWrite` policy we need to end the first branch
        // (which is taken if the condition is `true`) with a colon (`:`) and write the
        // second branch which is just a 0 value.
        if let proc::BoundsCheckPolicy::ReadZeroSkipWrite = policy {
            // Get the kind of the output value.
            let kind = match class {
                // Only sampled images can reach here since storage images
                // don't need bounds checks and depth images aren't implmented
                crate::ImageClass::Sampled { kind, .. } => kind,
                _ => unreachable!(),
            };

            // End the first branch
            write!(self.out, " : ")?;
            // Write the 0 value
            write!(self.out, "{}vec4(", glsl_scalar(kind, 4)?.prefix,)?;
            self.write_zero_init_scalar(kind)?;
            // Close the zero value constructor
            write!(self.out, ")")?;
            // Close the parantheses surrounding our ternary
            write!(self.out, ")")?;
        }

        Ok(())
    }

    fn write_named_expr(
        &mut self,
        handle: Handle<crate::Expression>,
        name: String,
        // The expression which is being named.
        // Generally, this is the same as handle, except in WorkGroupUniformLoad
        named: Handle<crate::Expression>,
        ctx: &back::FunctionCtx,
    ) -> BackendResult {
        match ctx.info[named].ty {
            proc::TypeResolution::Handle(ty_handle) => match self.module.types[ty_handle].inner {
                TypeInner::Struct { .. } => {
                    let ty_name = &self.names[&NameKey::Type(ty_handle)];
                    write!(self.out, "{ty_name}")?;
                }
                _ => {
                    self.write_type(ty_handle)?;
                }
            },
            proc::TypeResolution::Value(ref inner) => {
                self.write_value_type(inner)?;
            }
        }

        let base_ty_res = &ctx.info[named].ty;
        let resolved = base_ty_res.inner_with(&self.module.types);

        write!(self.out, " {name}")?;
        if let TypeInner::Array { base, size, .. } = *resolved {
            self.write_array_size(base, size)?;
        }
        write!(self.out, " = ")?;
        self.write_expr(handle, ctx)?;
        writeln!(self.out, ";")?;
        self.named_expressions.insert(named, name);

        Ok(())
    }

    /// Helper function that write string with default zero initialization for supported types
    fn write_zero_init_value(&mut self, ty: Handle<crate::Type>) -> BackendResult {
        let inner = &self.module.types[ty].inner;
        match *inner {
            TypeInner::Scalar { kind, .. } | TypeInner::Atomic { kind, .. } => {
                self.write_zero_init_scalar(kind)?;
            }
            TypeInner::Vector { kind, .. } => {
                self.write_value_type(inner)?;
                write!(self.out, "(")?;
                self.write_zero_init_scalar(kind)?;
                write!(self.out, ")")?;
            }
            TypeInner::Matrix { .. } => {
                self.write_value_type(inner)?;
                write!(self.out, "(")?;
                self.write_zero_init_scalar(crate::ScalarKind::Float)?;
                write!(self.out, ")")?;
            }
            TypeInner::Array { base, size, .. } => {
                let count = match size
                    .to_indexable_length(self.module)
                    .expect("Bad array size")
                {
                    proc::IndexableLength::Known(count) => count,
                    proc::IndexableLength::Dynamic => return Ok(()),
                };
                self.write_type(base)?;
                self.write_array_size(base, size)?;
                write!(self.out, "(")?;
                for _ in 1..count {
                    self.write_zero_init_value(base)?;
                    write!(self.out, ", ")?;
                }
                // write last parameter without comma and space
                self.write_zero_init_value(base)?;
                write!(self.out, ")")?;
            }
            TypeInner::Struct { ref members, .. } => {
                let name = &self.names[&NameKey::Type(ty)];
                write!(self.out, "{name}(")?;
                for (index, member) in members.iter().enumerate() {
                    if index != 0 {
                        write!(self.out, ", ")?;
                    }
                    self.write_zero_init_value(member.ty)?;
                }
                write!(self.out, ")")?;
            }
            _ => unreachable!(),
        }

        Ok(())
    }

    /// Helper function that write string with zero initialization for scalar
    fn write_zero_init_scalar(&mut self, kind: crate::ScalarKind) -> BackendResult {
        match kind {
            crate::ScalarKind::Bool => write!(self.out, "false")?,
            crate::ScalarKind::Uint => write!(self.out, "0u")?,
            crate::ScalarKind::Float => write!(self.out, "0.0")?,
            crate::ScalarKind::Sint => write!(self.out, "0")?,
        }

        Ok(())
    }

    /// Issue a memory barrier. Please note that to ensure visibility,
    /// OpenGL always requires a call to the `barrier()` function after a `memoryBarrier*()`
    fn write_barrier(&mut self, flags: crate::Barrier, level: back::Level) -> BackendResult {
        if flags.contains(crate::Barrier::STORAGE) {
            writeln!(self.out, "{level}memoryBarrierBuffer();")?;
        }
        if flags.contains(crate::Barrier::WORK_GROUP) {
            writeln!(self.out, "{level}memoryBarrierShared();")?;
        }
        writeln!(self.out, "{level}barrier();")?;
        Ok(())
    }

    /// Helper function that return the glsl storage access string of [`StorageAccess`](crate::StorageAccess)
    ///
    /// glsl allows adding both `readonly` and `writeonly` but this means that
    /// they can only be used to query information about the resource which isn't what
    /// we want here so when storage access is both `LOAD` and `STORE` add no modifiers
    fn write_storage_access(&mut self, storage_access: crate::StorageAccess) -> BackendResult {
        if !storage_access.contains(crate::StorageAccess::STORE) {
            write!(self.out, "readonly ")?;
        }
        if !storage_access.contains(crate::StorageAccess::LOAD) {
            write!(self.out, "writeonly ")?;
        }
        Ok(())
    }

    /// Helper method used to produce the reflection info that's returned to the user
    fn collect_reflection_info(&self) -> Result<ReflectionInfo, Error> {
        use std::collections::hash_map::Entry;
        let info = self.info.get_entry_point(self.entry_point_idx as usize);
        let mut texture_mapping = crate::FastHashMap::default();
        let mut uniforms = crate::FastHashMap::default();

        for sampling in info.sampling_set.iter() {
            let tex_name = self.reflection_names_globals[&sampling.image].clone();

            match texture_mapping.entry(tex_name) {
                Entry::Vacant(v) => {
                    v.insert(TextureMapping {
                        texture: sampling.image,
                        sampler: Some(sampling.sampler),
                    });
                }
                Entry::Occupied(e) => {
                    if e.get().sampler != Some(sampling.sampler) {
                        log::error!("Conflicting samplers for {}", e.key());
                        return Err(Error::ImageMultipleSamplers);
                    }
                }
            }
        }

        for (handle, var) in self.module.global_variables.iter() {
            if info[handle].is_empty() {
                continue;
            }
            match self.module.types[var.ty].inner {
                crate::TypeInner::Image { .. } => {
                    let tex_name = self.reflection_names_globals[&handle].clone();
                    match texture_mapping.entry(tex_name) {
                        Entry::Vacant(v) => {
                            v.insert(TextureMapping {
                                texture: handle,
                                sampler: None,
                            });
                        }
                        Entry::Occupied(_) => {
                            // already used with a sampler, do nothing
                        }
                    }
                }
                _ => match var.space {
                    crate::AddressSpace::Uniform | crate::AddressSpace::Storage { .. } => {
                        let name = self.reflection_names_globals[&handle].clone();
                        uniforms.insert(handle, name);
                    }
                    _ => (),
                },
            }
        }

        Ok(ReflectionInfo {
            texture_mapping,
            uniforms,
        })
    }
}

/// Structure returned by [`glsl_scalar`](glsl_scalar)
///
/// It contains both a prefix used in other types and the full type name
struct ScalarString<'a> {
    /// The prefix used to compose other types
    prefix: &'a str,
    /// The name of the scalar type
    full: &'a str,
}

/// Helper function that returns scalar related strings
///
/// Check [`ScalarString`](ScalarString) for the information provided
///
/// # Errors
/// If a [`Float`](crate::ScalarKind::Float) with an width that isn't 4 or 8
const fn glsl_scalar(
    kind: crate::ScalarKind,
    width: crate::Bytes,
) -> Result<ScalarString<'static>, Error> {
    use crate::ScalarKind as Sk;

    Ok(match kind {
        Sk::Sint => ScalarString {
            prefix: "i",
            full: "int",
        },
        Sk::Uint => ScalarString {
            prefix: "u",
            full: "uint",
        },
        Sk::Float => match width {
            4 => ScalarString {
                prefix: "",
                full: "float",
            },
            8 => ScalarString {
                prefix: "d",
                full: "double",
            },
            _ => return Err(Error::UnsupportedScalar(kind, width)),
        },
        Sk::Bool => ScalarString {
            prefix: "b",
            full: "bool",
        },
    })
}

/// Helper function that returns the glsl variable name for a builtin
const fn glsl_built_in(
    built_in: crate::BuiltIn,
    output: bool,
    targetting_webgl: bool,
) -> &'static str {
    use crate::BuiltIn as Bi;

    match built_in {
        Bi::Position { .. } => {
            if output {
                "gl_Position"
            } else {
                "gl_FragCoord"
            }
        }
        Bi::ViewIndex if targetting_webgl => "int(gl_ViewID_OVR)",
        Bi::ViewIndex => "gl_ViewIndex",
        // vertex
        Bi::BaseInstance => "uint(gl_BaseInstance)",
        Bi::BaseVertex => "uint(gl_BaseVertex)",
        Bi::ClipDistance => "gl_ClipDistance",
        Bi::CullDistance => "gl_CullDistance",
        Bi::InstanceIndex => "uint(gl_InstanceID)",
        Bi::PointSize => "gl_PointSize",
        Bi::VertexIndex => "uint(gl_VertexID)",
        // fragment
        Bi::FragDepth => "gl_FragDepth",
        Bi::PointCoord => "gl_PointCoord",
        Bi::FrontFacing => "gl_FrontFacing",
        Bi::PrimitiveIndex => "uint(gl_PrimitiveID)",
        Bi::SampleIndex => "gl_SampleID",
        Bi::SampleMask => {
            if output {
                "gl_SampleMask"
            } else {
                "gl_SampleMaskIn"
            }
        }
        // compute
        Bi::GlobalInvocationId => "gl_GlobalInvocationID",
        Bi::LocalInvocationId => "gl_LocalInvocationID",
        Bi::LocalInvocationIndex => "gl_LocalInvocationIndex",
        Bi::WorkGroupId => "gl_WorkGroupID",
        Bi::WorkGroupSize => "gl_WorkGroupSize",
        Bi::NumWorkGroups => "gl_NumWorkGroups",
    }
}

/// Helper function that returns the string corresponding to the address space
const fn glsl_storage_qualifier(space: crate::AddressSpace) -> Option<&'static str> {
    use crate::AddressSpace as As;

    match space {
        As::Function => None,
        As::Private => None,
        As::Storage { .. } => Some("buffer"),
        As::Uniform => Some("uniform"),
        As::Handle => Some("uniform"),
        As::WorkGroup => Some("shared"),
        As::PushConstant => Some("uniform"),
    }
}

/// Helper function that returns the string corresponding to the glsl interpolation qualifier
const fn glsl_interpolation(interpolation: crate::Interpolation) -> &'static str {
    use crate::Interpolation as I;

    match interpolation {
        I::Perspective => "smooth",
        I::Linear => "noperspective",
        I::Flat => "flat",
    }
}

/// Return the GLSL auxiliary qualifier for the given sampling value.
const fn glsl_sampling(sampling: crate::Sampling) -> Option<&'static str> {
    use crate::Sampling as S;

    match sampling {
        S::Center => None,
        S::Centroid => Some("centroid"),
        S::Sample => Some("sample"),
    }
}

/// Helper function that returns the glsl dimension string of [`ImageDimension`](crate::ImageDimension)
const fn glsl_dimension(dim: crate::ImageDimension) -> &'static str {
    use crate::ImageDimension as IDim;

    match dim {
        IDim::D1 => "1D",
        IDim::D2 => "2D",
        IDim::D3 => "3D",
        IDim::Cube => "Cube",
    }
}

/// Helper function that returns the glsl storage format string of [`StorageFormat`](crate::StorageFormat)
fn glsl_storage_format(format: crate::StorageFormat) -> Result<&'static str, Error> {
    use crate::StorageFormat as Sf;

    Ok(match format {
        Sf::R8Unorm => "r8",
        Sf::R8Snorm => "r8_snorm",
        Sf::R8Uint => "r8ui",
        Sf::R8Sint => "r8i",
        Sf::R16Uint => "r16ui",
        Sf::R16Sint => "r16i",
        Sf::R16Float => "r16f",
        Sf::Rg8Unorm => "rg8",
        Sf::Rg8Snorm => "rg8_snorm",
        Sf::Rg8Uint => "rg8ui",
        Sf::Rg8Sint => "rg8i",
        Sf::R32Uint => "r32ui",
        Sf::R32Sint => "r32i",
        Sf::R32Float => "r32f",
        Sf::Rg16Uint => "rg16ui",
        Sf::Rg16Sint => "rg16i",
        Sf::Rg16Float => "rg16f",
        Sf::Rgba8Unorm => "rgba8",
        Sf::Rgba8Snorm => "rgba8_snorm",
        Sf::Rgba8Uint => "rgba8ui",
        Sf::Rgba8Sint => "rgba8i",
        Sf::Rgb10a2Uint => "rgb10_a2ui",
        Sf::Rgb10a2Unorm => "rgb10_a2",
        Sf::Rg11b10Float => "r11f_g11f_b10f",
        Sf::Rg32Uint => "rg32ui",
        Sf::Rg32Sint => "rg32i",
        Sf::Rg32Float => "rg32f",
        Sf::Rgba16Uint => "rgba16ui",
        Sf::Rgba16Sint => "rgba16i",
        Sf::Rgba16Float => "rgba16f",
        Sf::Rgba32Uint => "rgba32ui",
        Sf::Rgba32Sint => "rgba32i",
        Sf::Rgba32Float => "rgba32f",
        Sf::R16Unorm => "r16",
        Sf::R16Snorm => "r16_snorm",
        Sf::Rg16Unorm => "rg16",
        Sf::Rg16Snorm => "rg16_snorm",
        Sf::Rgba16Unorm => "rgba16",
        Sf::Rgba16Snorm => "rgba16_snorm",

        Sf::Bgra8Unorm => {
            return Err(Error::Custom(
                "Support format BGRA8 is not implemented".into(),
            ))
        }
    })
}

fn is_value_init_supported(module: &crate::Module, ty: Handle<crate::Type>) -> bool {
    match module.types[ty].inner {
        TypeInner::Scalar { .. } | TypeInner::Vector { .. } | TypeInner::Matrix { .. } => true,
        TypeInner::Array { base, size, .. } => {
            size != crate::ArraySize::Dynamic && is_value_init_supported(module, base)
        }
        TypeInner::Struct { ref members, .. } => members
            .iter()
            .all(|member| is_value_init_supported(module, member.ty)),
        _ => false,
    }
}