Drawing a triangle with Metal 4

At a glance

Project structure

Source bundle/
├── Application/
│   ├── main.m
│   ├── AppDelegate.h
│   ├── AppDelegate.m
│   ├── WindowSceneDelegate.h
│   └── WindowSceneDelegate.m
├── Metal 4 renderer/
│   ├── Metal4Renderer.h
│   └── Metal4Renderer.m
├── Metal renderer/
│   ├── MetalRenderer.h
│   └── MetalRenderer.m
└── View controller/
    ├── MetalKitViewDelegate.h
    ├── MetalKitViewDelegate.m
    └── ViewController.h

Structure observations

• Architecturally prominent files are ranked from entry points and role-named declarations; resource-only paths are omitted.
• Primary languages: C, C/Objective-C header, Metal, Objective-C.
• The verified tree contains 9 project/configuration file(s) and 8 source declaration(s).

Overall architecture

flowchart LR
    N1["main"]
    N2["ViewController"]
    N3["Metal4Renderer"]
    N4["metal_stdlib APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

Application/main.m:19 — architecture anchor

#if defined(TARGET_IOS) || defined(TARGET_TVOS)
int main(int argc, char * argv[]) {
    // ...
#error No simulator support for Metal API for this SDK version.  Must build for a device
    // ...
}
#endif

Interpretation

The arrows summarize the source-visible entry, role-named types or folders, and framework direction; when nodes come from structural folders, the sequence is a high-level interpretation rather than proof that every adjacent node calls the next. Ownership is claimed only where the next section cites a stored property or assignment. The diagram is intentionally limited to the dominant path into Metal.

Ownership and state

classDiagram
    WindowSceneDelegate o-- UIWindow : window
    Metal4Renderer o-- id : device
    Metal4Renderer o-- id : defaultLibrary
    MetalRenderer o-- id : device

Ownership evidence

Application/WindowSceneDelegate.h:13 — stored dependency or nearest verified ownership anchor

@interface WindowSceneDelegate : UIResponder <UIWindowSceneDelegate>

@property (nonatomic, strong) UIWindow *window;

@end

Composition arrows indicate a source-visible construction expression or locally owned value state; aggregation means the owner stores or receives a dependency without proving exclusive lifetime ownership.

Concurrency, scheduling, and thread safety

Evidence limit: actor isolation, async/await, or Task creation does not by itself prove background-thread execution; Sendable conformance alone does not prove thread-safe mutation.

No source-visible execution, scheduling, or synchronization boundary was found in the indexed source.

@MainActor/MainActor.run, DispatchQueue.main, and RunLoop.main are reported as distinct isolation, queue, and event-loop mechanisms. A plain Task is kept separate from Task.detached; neither is labeled as a background thread.

State propagation, frameworks, and dependencies

Evidence limit: an import proves a source-level compilation dependency at the cited line; it does not prove runtime use, architectural adoption, or whether a Swift package is a direct application dependency.

receive(on:) describes downstream delivery scheduling, while subscribe(on:) describes upstream subscription/request/cancel scheduling. An import Combine alone establishes neither behavior nor a Store, reducer, Redux, or other application architecture.

Class and protocol design

Renderer common/RendererProtocol.h:11 — representative type boundary

@protocol Renderer <NSObject>
// ...
@end

The source explicitly defines local protocol relationships: Metal4Renderer → Renderer, MetalRenderer → Renderer.

Access control

Reference code

Application/WindowSceneDelegate.h:13 — representative boundary

@interface WindowSceneDelegate : UIResponder <UIWindowSceneDelegate>

@property (nonatomic, strong) UIWindow *window;

@end

Swift declarations without a modifier are internal; explicit private, fileprivate, private(set), public, or open entries above are interpreted by language semantics. Objective-C/C samples instead rely on header and implementation boundaries, which are not equivalent to Swift lexical privacy.

Logic ownership and placement

Design patterns

Main application flow

sequenceDiagram
    participant Metal4Renderer
    participant device
    participant residencySet
    participant commandQueue
    Metal4Renderer->>Metal4Renderer: init()
    Metal4Renderer->>device: newMTL4CommandQueue()
    Metal4Renderer->>device: newCommandBuffer()
    Metal4Renderer->>device: newDefaultLibrary()
    Metal4Renderer->>residencySet: addAllocation()
    Metal4Renderer->>residencySet: commit()
    Metal4Renderer->>commandQueue: addResidencySet()
    Metal4Renderer->>Metal4Renderer: updateViewportSize()

Reference code

Metal 4 renderer/Metal4Renderer.m:129 — initWithMetalKitView()

- (nonnull instancetype) initWithMetalKitView:(nonnull MTKView *) view
{
    // ...
    self = [super init];
    if (nil == self) { return nil; }
    _device = view.device;
    commandQueue = [self.device newMTL4CommandQueue];
    commandBuffer = [self.device newCommandBuffer];
    _defaultLibrary = [self.device newDefaultLibrary];
    triangleVertexBuffers = [self makeTriangleDataBuffers:kMaxFramesInFlight];
    argumentTable = [self makeArgumentTable];
    residencySet = [self makeResidencySet];
    commandAllocators = [self makeCommandAllocators:kMaxFramesInFlight];
    viewportSizeBuffer = [self.device newBufferWithLength:sizeof(viewportSize)
                                                  options:MTLResourceStorageModeShared];
    renderPipelineState = [self compileRenderPipeline:view.colorPixelFormat];
    frameNumber = 0;
    sharedEvent = [self.device newSharedEvent];
    sharedEvent.signaledValue = frameNumber;
    [residencySet addAllocation:viewportSizeBuffer];
    for (id<MTLBuffer> triangleVertexBuffer in triangleVertexBuffers) {
        [residencySet addAllocation:triangleVertexBuffer];
    }
    [residencySet commit];
    [commandQueue addResidencySet:residencySet];
    [commandQueue addResidencySet:((CAMetalLayer *)view.layer).residencySet];
    [self updateViewportSize:view.drawableSize];
    return self;
}

Naming conventions

• Types: Controller: ViewController; Delegate: AppDelegate, MetalKitViewDelegate, WindowSceneDelegate; Renderer: Metal4Renderer, MetalRenderer, Renderer.
• Protocols: Renderer.
• Methods: application, scene, sceneDidDisconnect, initWithMetalKitView, updateViewportSize, renderFrameToView, isMissingRequirementsFromView.
• Files: Application/AppDelegate.h, Application/AppDelegate.m, Application/WindowSceneDelegate.h, Application/WindowSceneDelegate.m, Metal 4 renderer/Metal4Renderer.h, Metal 4 renderer/Metal4Renderer.m.

Architecture takeaways

• main is the main source-visible entry or composition anchor for this sample.
• Framework work reaches metal_stdlib, simd through a deliberately small high-level chain; the detailed API graph remains inside the cited implementation files.
• Stored-property evidence identifies lifecycle collaboration; it does not by itself prove exclusive object ownership.
• Access-control conclusions separate verified language visibility from the likely design rationale.
• Local protocol relationships provide an explicit substitution boundary.

Source map

• Official Apple documentation