Capturing Metal commands programmatically

At a glance

Project structure

Source bundle/
├── Application/
│   ├── AAPLViewController.m
│   ├── main.m
│   └── AAPLViewController.h
└── Renderer/
    ├── AAPLShaders.metal
    ├── AAPLRenderer.m
    ├── AAPLCaptureManager.m
    ├── AAPLShaderTypes.h
    ├── AAPLCaptureManager.h
    └── AAPLRenderer.h

Structure observations

• The entry/composition boundary and renderer or operation boundary are separate in the source; AAPLRenderer is the principal feature coordinator.
• GPU-specific logic stays in Metal shader files; shared headers bridge host/shader layouts where present.
• The tree above is intentionally pruned to composition, resource, and shader files.

Overall architecture

flowchart LR
    N1["AAPLViewController"]
    N2["AAPLRenderer"]
    N3["capture-scope lifecycle"]
    N4["captured Metal command stream"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

Application/AAPLViewController.m:43 — feature handoff or setup anchor

    MTLCaptureManager *captureManager = MTLCaptureManager.sharedCaptureManager;

    if (![captureManager supportsDestination:MTLCaptureDestinationDeveloperTools])
    {
        _captureInXcodeButton.enabled = NO;
    }

    if (![captureManager supportsDestination:MTLCaptureDestinationGPUTraceDocument])

Interpretation

This is the dominant control/data path: platform code composes AAPLRenderer; that object controls capture-scope lifecycle; GPU-visible work ends in captured Metal command stream. The arrows summarize responsibility transfer, not a claim that every node directly calls the next.

Ownership and state

classDiagram
    AAPLViewController *-- AAPLRenderer : _renderer

Ownership evidence

Application/AAPLViewController.m:37 — AAPLViewController creates and stores _renderer

    _renderer = [[AAPLRenderer alloc] initWithMetalKitView:_view];

    [_renderer mtkView:_view drawableSizeWillChange:_view.bounds.size];

    _view.delegate = _renderer;

    MTLCaptureManager *captureManager = MTLCaptureManager.sharedCaptureManager;

Class and protocol design

Framework delegate conformance is a callback seam; the source does not justify calling the whole app protocol-oriented.

Access control

This sample does not use Swift private, fileprivate, or public for its native boundary. Objective-C/Objective-C++ use header versus implementation placement, C++ uses access specifiers/linkage, Python uses module conventions, and Metal entry points cross a compiled-library boundary; these are not Swift access levels.

Logic ownership and placement

Shader boundary reference

Renderer/AAPLShaders.metal:27 — representative GPU entry/helper

vertex ColorInOut vertexShader(Vertex in [[stage_in]],
                               constant Uniforms & uniforms [[ buffer(BufferIndexUniforms) ]])
{
    // ...
}

Design patterns

Naming conventions

• Role suffixes make ownership visible: AAPLViewController, AAPLRenderer, AAPLCaptureManager.
• Method names describe setup or encoding actions: viewDidLoad, captureInXcode, captureToFile, setupCaptureInXcode, setupCaptureToFile, captureWithDescriptor, startCapture.
• Shader entry points use stage/operation names: vertexShader, fragmentShader.
• AAPL is a sample namespace prefix, not a recommendation for production module naming; retain semantic suffixes such as Renderer, Manager, Scene, or Adapter.

Architecture takeaways

• Keep AAPLViewController focused on composition; AAPLRenderer is the owner of capture-scope lifecycle.
• Treat captured Metal command stream as a separate execution/compilation boundary with explicit resource and data-layout contracts.
• The verified ownership edge is AAPLViewController → _renderer; broader exclusive ownership is not inferred.
• Access-control rationale follows concrete language boundaries rather than translating every header or shader symbol into Swift terms.

Source map

• Official Apple documentation