metal-gpu

How to use

Copy the installation command and review the source package before installing it in your own agent environment.
Check the source document for required tools, credentials and supported hosts.
Describe your input and desired deliverable; review the output against the source material.

npx skills add https://github.com/ios-agent/iosagent.dev --skill metal-gpu

Before you start

Installation does not include a model subscription, API allowance or permission to access your files.
Repository stars and installation counts describe activity, not an independent quality or security test.

Original skill document

Rendered from the source repository. Headings, examples, code, tables, links, and referenced images are preserved.

Metal GPU Code Skill

Write production-quality Metal code with correct patterns, optimal performance, and clear explanations.

When to Read References

For detailed API topology, Metal 4 specifics, and Apple Silicon optimization patterns, read:

/mnt/skills/user/metal-gpu/references/metal-api-guide.md

Core Principles

Always start with the device: MTLCreateSystemDefaultDevice() — every Metal workflow begins here
Command pattern: Device → Command Queue → Command Buffer → Command Encoder → Commit
Shaders are MSL (Metal Shading Language): C++14-based, with Metal-specific types and attributes
Resource management matters: Use appropriate storage modes, avoid unnecessary copies
Triple buffering for render loops to keep CPU and GPU in parallel

Quick Reference: Metal Command Pipeline

MTLDevice
  └─ makeCommandQueue() → MTLCommandQueue
       └─ makeCommandBuffer() → MTLCommandBuffer
            ├─ makeRenderCommandEncoder(descriptor:) → MTLRenderCommandEncoder
            ├─ makeComputeCommandEncoder() → MTLComputeCommandEncoder
            └─ makeBlitCommandEncoder() → MTLBlitCommandEncoder

Writing Shaders (MSL)

Use Metal Shading Language. Always include:

#include <metal_stdlib> and using namespace metal;
Correct attribute qualifiers: [[vertex_id]], [[position]], [[stage_in]], [[buffer(n)]], [[texture(n)]]
Proper address space qualifiers: device, constant, threadgroup, thread

Vertex Shader Pattern

metal

#include <metal_stdlib>
using namespace metal;

struct VertexIn {
    float3 position [[attribute(0)]];
    float3 normal   [[attribute(1)]];
    float2 texCoord [[attribute(2)]];
};

struct VertexOut {
    float4 position [[position]];
    float3 normal;
    float2 texCoord;
};

vertex VertexOut vertex_main(VertexIn in [[stage_in]],
                             constant float4x4 &mvp [[buffer(1)]]) {
    VertexOut out;
    out.position = mvp * float4(in.position, 1.0);
    out.normal = in.normal;
    out.texCoord = in.texCoord;
    return out;
}

Fragment Shader Pattern

metal

fragment float4 fragment_main(VertexOut in [[stage_in]],
                              texture2d<float> albedo [[texture(0)]],
                              sampler texSampler [[sampler(0)]]) {
    float4 color = albedo.sample(texSampler, in.texCoord);
    return color;
}

Compute Kernel Pattern

metal

kernel void compute_main(device float *input  [[buffer(0)]],
                         device float *output [[buffer(1)]],
                         uint id [[thread_position_in_grid]]) {
    output[id] = input[id] * 2.0;
}

Swift-Side Setup Patterns

Render Pipeline Setup

swift

let device = MTLCreateSystemDefaultDevice()!
let commandQueue = device.makeCommandQueue()!

// Load shaders
let library = device.makeDefaultLibrary()!
let vertexFunction = library.makeFunction(name: "vertex_main")
let fragmentFunction = library.makeFunction(name: "fragment_main")

// Pipeline descriptor
let pipelineDescriptor = MTLRenderPipelineDescriptor()
pipelineDescriptor.vertexFunction = vertexFunction
pipelineDescriptor.fragmentFunction = fragmentFunction
pipelineDescriptor.colorAttachments[0].pixelFormat = .bgra8Unorm

// Vertex descriptor
let vertexDescriptor = MTLVertexDescriptor()
vertexDescriptor.attributes[0].format = .float3  // position
vertexDescriptor.attributes[0].offset = 0
vertexDescriptor.attributes[0].bufferIndex = 0
vertexDescriptor.layouts[0].stride = MemoryLayout<SIMD3<Float>>.stride
pipelineDescriptor.vertexDescriptor = vertexDescriptor

let pipelineState = try! device.makeRenderPipelineState(descriptor: pipelineDescriptor)

Compute Pipeline Setup

swift

let computeFunction = library.makeFunction(name: "compute_main")!
let computePipeline = try! device.makeComputePipelineState(function: computeFunction)

let commandBuffer = commandQueue.makeCommandBuffer()!
let encoder = commandBuffer.makeComputeCommandEncoder()!
encoder.setComputePipelineState(computePipeline)
encoder.setBuffer(inputBuffer, offset: 0, index: 0)
encoder.setBuffer(outputBuffer, offset: 0, index: 1)

let gridSize = MTLSize(width: elementCount, height: 1, depth: 1)
let threadGroupSize = MTLSize(
    width: min(computePipeline.maxTotalThreadsPerThreadgroup, elementCount),
    height: 1, depth: 1
)
encoder.dispatchThreads(gridSize, threadsPerThreadgroup: threadGroupSize)
encoder.endEncoding()
commandBuffer.commit()

MetalKit View Rendering

swift

import MetalKit

class Renderer: NSObject, MTKViewDelegate {
    let device: MTLDevice
    let commandQueue: MTLCommandQueue
    let pipelineState: MTLRenderPipelineState

    func draw(in view: MTKView) {
        guard let drawable = view.currentDrawable,
              let descriptor = view.currentRenderPassDescriptor else { return }

        let commandBuffer = commandQueue.makeCommandBuffer()!
        let encoder = commandBuffer.makeRenderCommandEncoder(descriptor: descriptor)!

        encoder.setRenderPipelineState(pipelineState)
        // Set buffers, draw primitives...
        encoder.drawPrimitives(type: .triangle, vertexStart: 0, vertexCount: 3)

        encoder.endEncoding()
        commandBuffer.present(drawable)
        commandBuffer.commit()
    }
}

Performance Best Practices

Storage modes: Use .shared on Apple Silicon (unified memory), .private for GPU-only data, .managed on Intel Macs
Triple buffering: Rotate 3 buffers with a semaphore to avoid CPU/GPU stalls
Avoid per-frame allocations: Reuse buffers and command encoders
Use `dispatchThreads` over `dispatchThreadgroups` when possible (Apple Silicon)
Prefer tile-based deferred rendering patterns on Apple GPUs — use imageblocks and tile shaders
Compile pipelines ahead of time: Pipeline creation is expensive, do it at load time
Use Metal GPU frame capture in Xcode to profile and debug

Common Mistakes to Avoid

Forgetting encoder.endEncoding() before committing
Mismatched buffer indices between Swift and MSL
Using wrong pixel format for render targets
Not handling nil from optional Metal API calls
Blocking the main thread waiting for GPU completion — use addCompletedHandler instead
Forgetting to set the vertex descriptor when using [[stage_in]]

Metal 4 Notes

Metal 4 introduces a modernized core API. Key changes:

New compilation API for finer shader compilation control
Updated command encoding patterns
See references/metal-api-guide.md for the full Metal 4 API topology

Frameworks Ecosystem

Framework	Purpose
Metal	Direct GPU access, shaders, pipelines
MetalKit	View management, texture loading, model I/O
MetalFX	Upscaling (temporal/spatial) for performance
Metal Performance Shaders	Optimized compute & image processing kernels
Compositor Services	Stereoscopic rendering for visionOS
RealityKit	High-level 3D rendering (uses Metal underneath)

How to use

Before you start

Metal GPU Code Skill

When to Read References

Core Principles

Quick Reference: Metal Command Pipeline

Writing Shaders (MSL)

Vertex Shader Pattern

Fragment Shader Pattern

Compute Kernel Pattern

Swift-Side Setup Patterns

Render Pipeline Setup

Compute Pipeline Setup

MetalKit View Rendering

Performance Best Practices

Common Mistakes to Avoid

Metal 4 Notes

Frameworks Ecosystem

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