Metal device, command queue, and CAMetalLayer setup #114

Phase 12: Metal GPU Compositor (1/7)#

Goal: Set up the foundational Metal infrastructure in the platform crate.

Requirements#

• Add Metal framework FFI bindings to platform crate:

  • MTLCreateSystemDefaultDevice() — obtain default GPU device
  • MTLDevice protocol: newCommandQueue, newLibraryWithSource:options:error:, newRenderPipelineStateWithDescriptor:error:, newBufferWithBytes:length:options:, newTextureWithDescriptor:
  • MTLCommandQueue: commandBuffer
  • MTLCommandBuffer: renderCommandEncoderWithDescriptor:, presentDrawable:, commit, waitUntilCompleted
  • CAMetalLayer: setDevice:, setPixelFormat:, nextDrawable, setFramebufferOnly:
  • CAMetalDrawable: texture
  • MTLRenderPassDescriptor setup

• Replace WeView's drawRect:-based CGImage blitting with a CAMetalLayer-backed view:

  • Set the view's wantsLayer = YES and replace backing layer with CAMetalLayer
  • Configure pixel format (MTLPixelFormatBGRA8Unorm)
  • Set drawable size to match view size in points × backing scale factor

• Implement basic "clear to color" proof-of-concept:

  • Create command buffer, get next drawable
  • Create render pass descriptor targeting drawable texture
  • Set clear color, encode empty render pass
  • Present drawable and commit

• Double-buffered presentation via CAMetalLayer.nextDrawable

Acceptance Criteria#

• cargo run -p we-browser opens a window with a Metal-rendered solid color background
• Resize correctly updates the CAMetalLayer drawable size
• All new code is in platform crate (unsafe allowed here)
• No external crate dependencies
• cargo clippy --workspace -- -D warnings passes
• cargo test --workspace passes