Problem

The Metal backend unconditionally configures every render pipeline state for two color attachments (for i in 0..2) plus depth + stencil at Depth32Float_Stencil8. MTKView by default exposes only color attachment 0 and depthStencilPixelFormat = MTLPixelFormatInvalid. With Metal validation on, the first draw asserts:

-[MTLDebugRenderCommandEncoder setRenderPipelineState:]:1654: failed assertion `Set Render Pipeline State Validation
For color attachment 1, the renderPipelineState pixelFormat must be MTLPixelFormatInvalid, as no texture is set.
For depth attachment, the renderPipelineState pixelFormat must be MTLPixelFormatInvalid, as no texture is set.
For stencil attachment, the renderPipelineState pixelFormat must be MTLPixelFormatInvalid, as no texture is set.

Hit this trying to switch a 2D macroquad app to the Metal backend on an iPhone 17 simulator (iOS 27 beta).

Fix

Two changes in graphics/metal.rs::new_pipeline:

1. Loop only over color attachment 0 (for i in 0..1) — miniquad's Metal backend doesn't expose multiple render targets, so attachment 1 should remain Invalid.
2. Read the view's depthStencilPixelFormat and pass it through to the pipeline's depth + stencil attachment formats — MTLPixelFormatInvalid when MTKView has no depth/stencil, which is the default.

After this, the pipeline state's attachment formats match whatever the encoder actually has bound, and Metal validation accepts every draw.

Tested on

iPhone 17 simulator on iOS 27 beta — Metal validation crash gone, app launches and renders into the simulator.