Game Porting Toolkit 4 Agentic Skills & GPU Debugging Tools

import Metal
import MetalKit

// MARK: - Metal 4 Resource Residency & Explicit Synchronization
// This pattern mirrors what GPTK4 agentic skills teach agents porting D3D12 engines.

func setupMetal4ResidencyAndBarrier(device: MTLDevice, view: MTKView) {
    guard let commandQueue = device.makeCommandQueue() else { return }

    // 1. Create a residency set — Metal 4 requires explicit GPU resource registration.
    //    Without this, the GPU cannot access the texture, producing silent wrong results.
    let residencySetDescriptor = MTLResidencySetDescriptor()
    residencySetDescriptor.initialCapacity = 16
    guard let residencySet = try? device.makeResidencySet(descriptor: residencySetDescriptor) else { return }

    // 2. Allocate a render target texture.
    let textureDescriptor = MTLTextureDescriptor.texture2DDescriptor(
        pixelFormat: .rgba16Float,
        width: 1920,
        height: 1080,
        mipmapped: false
    )
    textureDescriptor.usage = [.renderTarget, .shaderRead]
    // Use private storage for GPU-only resources (best practice on Apple silicon).
    textureDescriptor.storageMode = .private
    guard let colorTarget = device.makeTexture(descriptor: textureDescriptor) else { return }

    // 3. Register ALL resources before any GPU work begins.
    residencySet.addAllocation(colorTarget)
    residencySet.commit()

    // 4. Build command buffer and attach the residency set.
    guard let commandBuffer = commandQueue.makeCommandBuffer() else { return }
    commandBuffer.addResidencySet(residencySet)

    // 5. Geometry/color pass.
    let colorAttachment = MTLRenderPassDescriptor()
    colorAttachment.colorAttachments[0].texture = colorTarget
    colorAttachment.colorAttachments[0].loadAction = .clear
    colorAttachment.colorAttachments[0].storeAction = .store
    colorAttachment.colorAttachments[0].clearColor = MTLClearColor(red: 0, green: 0, blue: 0, alpha: 1)

    if let renderEncoder = commandBuffer.makeRenderCommandEncoder(descriptor: colorAttachment) {
        // ... draw scene geometry ...
        renderEncoder.endEncoding()
    }

    // 6. Explicit producer-consumer barrier between render and compute passes.
    //    GPTK4 skills map D3D12 resource states to Metal 4's barrier model.
    //    Without this, broad blanket barriers or missing barriers cause silent corruption.
    if let barrierEncoder = commandBuffer.makeBlitCommandEncoder() {
        // Synchronize colorTarget: render wrote it, compute will read it.
        barrierEncoder.textureBarrier()
        barrierEncoder.endEncoding()
    }

    // 7. Compute post-process pass (e.g., tone mapping / SSAO) reads colorTarget.
    let computeDescriptor = MTLComputePassDescriptor()
    if let computeEncoder = commandBuffer.makeComputeCommandEncoder(descriptor: computeDescriptor) {
        // bind colorTarget as shader read, dispatch tone-mapping kernel...
        computeEncoder.endEncoding()
    }

    commandBuffer.commit()
    commandBuffer.waitUntilCompleted()

    print("Frame complete. Residency set held \(residencySet.allocations.count) allocation(s).")
}