Metal render pipeline: 2D shaders and vertex format #115

Phase 12: Metal GPU Compositor (2/7)#

Goal: Implement MSL shaders and render pipeline state for 2D quad rendering.

Depends on: Metal device, command queue, and CAMetalLayer setup

Requirements#

• Write Metal Shading Language (MSL) shaders compiled at runtime via newLibraryWithSource::

  • Vertex shader: transform 2D vertex positions, pass through color and texture coordinates
  • Fragment shader: support two modes — solid color fill and textured (sampled from texture with color tint)
  • Use a uniform for the viewport size to convert pixel coordinates to normalized device coordinates

• Define vertex format:

  struct Vertex {
      position: [f32; 2],    // pixel coordinates
      color: [f32; 4],       // RGBA
      tex_coord: [f32; 2],   // UV coordinates (0,0 for solid rects)
      use_texture: f32,      // 0.0 = solid color, 1.0 = textured
  }
  

• Create MTLRenderPipelineState:

  • Configure vertex descriptor matching the Vertex struct
  • Set pixel format to match CAMetalLayer (BGRA8Unorm)
  • Enable alpha blending: source * sourceAlpha + dest * (1 - sourceAlpha)

• Implement a MetalRenderer struct (or extend existing platform code):

  • Hold device, command queue, pipeline state references
  • Method to build a vertex buffer from a list of 2D quads
  • Method to encode draw calls for a batch of quads

• Proof-of-concept: render a colored rectangle using the Metal pipeline

Acceptance Criteria#

• Can render solid-color rectangles via Metal pipeline
• Alpha blending works correctly for semi-transparent fills
• Shader compiles at runtime without errors
• Vertex data is efficiently batched into a single buffer
• No external crate dependencies
• cargo clippy --workspace -- -D warnings passes
• cargo test --workspace passes