Framebuffers: post-processing

modules/engine/mrblib/engine.rb

@@ -117,11 +117,12 @@ def shutdown
     def main
       @logger.info "Audio Module: #{Audio::NAME}"
       @logger.debug 'Starting main loop'
-      clear_bits = GL2::GL_COLOR_BUFFER_BIT | GL2::GL_DEPTH_BUFFER_BIT
       until @screen.should_close?
-        GL2.glClear clear_bits
         Audio.update
-        @step.call self, @fps.restart
+        @screen.render do
+          @screen.clear
+          @step.call self, @fps.restart
+        end
         @screen.title = sprintf "FPS: %d", @fps.fps
         @screen.swap
         GLFW.poll_events

modules/graphics/include/moon/texture.hxx

@@ -12,8 +12,10 @@ namespace Moon {
   class Texture {
   public:
     Texture(std::string filename);
+    Texture(int width, int height);
     ~Texture();
     void Bind();
+    void Attach();
     GLint GetWidth();
     GLint GetHeight();
     GLuint GetID();

modules/graphics/mrblib/framebuffer.rb

@@ -0,0 +1,74 @@
+module Moon
+  class Framebuffer
+
+    def initialize
+      @texture = Texture.new(600, 800)
+      @vbo = VertexBuffer.new(VertexBuffer::STATIC_DRAW)
+      @shader = Shader.load('todo', 'todo')
+
+      # TODO: generate the 0->1 vertices for a quad that covers entire screen
+
+      # TODO: handle window resizes, texture needs to be resized
+
+      # Depth buffer RBO
+      rbo_depth = GL2::glGenRenderbuffers(1).first
+      GL2::glBindRenderbuffer(GL2::GL_RENDERBUFFER, rbo_depth)
+      GL2::glRenderbufferStorage(GL2::GL_RENDERBUFFER, GL2::GL_DEPTH_COMPONENT16, screen_width, screen_height)
+      GL2::glBindRenderbuffer(GL2::GL_RENDERBUFFER, 0)
+
+      # Framebuffer to link everything together
+      @fbo = GL2::glGenFramebuffers(1).first
+      GL2::glBindFramebuffer(GL2::GL_FRAMEBUFFER, @fbo)
+
+      # attach the texture to FBO color attachment point
+      GL2::glFramebufferTexture2D(
+        GL2::GL_FRAMEBUFFER,
+        GL2::GL_COLOR_ATTACHMENT0,
+        GL2::GL_TEXTURE_2D,
+        @texture.id,
+        0
+      )
+
+      # attach the renderbuffer to depth attachment point
+      GL2::glFramebufferRenderbuffer(
+        GL2::GL_FRAMEBUFFER,
+        GL2::GL_DEPTH_ATTACHMENT,
+        GL2::GL_RENDERBUFFER,
+        rbo_depth
+      )
+
+      if ((status = GL2::glCheckFramebufferStatus(GL2::GL_FRAMEBUFFER)) != GL2::GL_FRAMEBUFFER_COMPLETE)
+        fprintf(stderr, "glCheckFramebufferStatus: error %p", status)
+        return 0
+      end
+      glBindFramebuffer(GL_FRAMEBUFFER, 0)
+    end
+
+    def bind
+      # set rendering destination to FBO
+      GL2::glBindFramebuffer(GL2::GL_FRAMEBUFFER, @fbo)
+
+      # clear buffers
+      clear_bits = GL2::GL_COLOR_BUFFER_BIT | GL2::GL_DEPTH_BUFFER_BIT
+      GL2.glClear clear_bits
+
+      # draw a scene to a texture directly
+      yield
+
+      # unbind FBO
+      GL2::glBindFramebuffer(GL2::GL_FRAMEBUFFER, 0)
+    end
+
+    def render
+      @shader.use
+      @shader.set_uniform 'tex0', Renderer.instance.bind_texture(@texture)
+      glDisable(GL_DEPTH_TEST)
+      @vbo.render OpenGL::TRIANGLE_STRIP
+    end
+
+    def terminate
+      # TODO: delete FBO & RBO
+    end
+
+  end
+end

modules/graphics/mrblib/screen.rb

@@ -120,6 +120,7 @@ def shutdown
 
     private def initialize_clear_color
       @clear_color = Vector4.new 0, 0, 0, 0
+      @clear_bits = GL2::GL_COLOR_BUFFER_BIT | GL2::GL_DEPTH_BUFFER_BIT
       self.clear_color = @clear_color
     end
 
@@ -129,6 +130,22 @@ def shutdown
 
     private def initialize_renderer
       Moon::Renderer.instance = Moon::Renderer.new
+      @framebuffer = Moon::Framebuffer.new
+    end
+
+    # magically wraps the render calls in a two pass render (first render to
+    # framebuffer, then render the FBO to screen with a shader). Allows us to do
+    # post-processing effects (screen toning, warping, etc).
+    def render(&block)
+      # first pass (clear is called inside main)
+      @framebuffer.bind(&block)
+      # second pass
+      clear
+      @framebuffer.render # render the fbo
+    end
+
+    def clear
+      GL2.glClear @clear_bits
     end
 
     # @param [Vector4] color

modules/graphics/src/texture.cxx

@@ -22,6 +22,21 @@ namespace Moon {
     glBindTexture(GL_TEXTURE_2D, 0);
   };
 
+  Texture::Texture(int width, int height)
+  {
+    float border_color[4] = { 0.0, 0.0, 0.0, 0.0 };
+    // Generate empty (RGB) texture
+    glGenTextures(1, &m_gl_texture_id);
+    glBindTexture(GL_TEXTURE_2D, m_gl_texture_id);
+    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, NULL);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_BORDER);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_BORDER);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
+    glTexParameterfv(GL_TEXTURE_2D, GL_TEXTURE_BORDER_COLOR, border_color);
+    glBindTexture(GL_TEXTURE_2D, 0);
+  };
+
   Texture::~Texture() {
     //Delete texture
     if (m_gl_texture_id != 0) {
@@ -44,4 +59,9 @@ namespace Moon {
   void Texture::Bind() {
     glBindTexture(GL_TEXTURE_2D, m_gl_texture_id);
   };
+
+  void Texture::Attach() {
+    // Attach it to currently bound framebuffer object
+    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, m_gl_texture_id, 0);
+  };
 }