Termux: unable to determine default font. Failed to locate font for family DejaVu Sans

[Quackdoc]

Bug Description

Cannot launch slint program (krokiet) on termux.

I am trying to run a program called krokiet on termux but it seems to fail due to font issues (Worth noting wayland is needed because when cross compiling for some reason it can't find the display server)

➜  ~ XDG_RUNTIME_DIR=$PREFIX/tmp WAYLAND_DISPLAY=wayland-2 XDG_DATA_DIRS=$PREFIX/glibc/share RUST_BACKTRACE=1 grun ./krokiet
03:26:35.195 [INFO] czkawka_core::common: App version: 8.0.0, release mode, rust 1.83.0 (2024-11-26), os Linux Unknown [aarch64 64-bit], 6 cpu/threads, features(0): []
thread 'main' panicked at /home/quack/.cargo/registry/src/index.crates.io-6f17d22bba15001f/i-slint-common-1.8.0/sharedfontdb.rs:165:13:
Unable to determine default font. Failed to locate font for family DejaVu Sans
stack backtrace:
   0: rust_begin_unwind
   1: core::panicking::panic_fmt
   2: i_slint_common::sharedfontdb::init_fontdb
   3: std::sys::thread_local::native::lazy::Storage<T,D>::initialize
   4: i_slint_core::graphics::image::svg::load_from_data
   5: i_slint_core::graphics::image::cache::ImageCache::load_image_from_embedded_data
   6: i_slint_core::graphics::image::load_image_from_embedded_data
   7: krokiet::slint_generatedMainWindow::InnerMainWindow::init
   8: krokiet::slint_generatedMainWindow::MainWindow::new
   9: krokiet::main
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

Reproducible Code (if applicable)

No response

Environment Details

• Slint Version: 1.8
• Platform/OS: Android Termux
• Programming Language: Rust
• Backend/Renderer: winit software

Product Impact

How to test:

1. Build krokiet with cargo build --release --target aarch64-unknown-linux-gnu --no-default-features --features "winit_software"

2. copy to termux (setup with termux-x11)

3. launch sway termux-x11 :1 -xstartup "XDG_RUNTIME_DIR=$PREFIX/tmp sway"

4. try to launch the program XDG_RUNTIME_DIR=$PREFIX/tmp WAYLAND_DISPLAY=wayland-2 XDG_DATA_DIRS=$PREFIX/glibc/share RUST_BACKTRACE=1 grun ./krokiet

this bug prevents use of slint on termux.

[tronical]

This error message indicates that while fontconfig says the font for "Sans Serif" is "DejaVu Sans", that font can't be found in any directories that are scanned for fonts.

Where in your target environment for the krokiet process (sysroot?) are your fonts located?

[ogoffart]

Ideally we shouldn't panic in that case, but somehow return an error from run() or something like that.

[tronical]

Yes, that's #2556.

[tronical]

I'll convert this into a discussion, as this is most likely a setup issue. Happy to continue triaging there.