Creating a custom Metal view

At a glance

Project structure

Source bundle/
└── Application/
    ├── main.m
    ├── AAPLAppDelegate.h
    ├── AAPLView.h
    ├── AAPLAppDelegate.m
    ├── AAPLView.m
    ├── AAPLViewController.h
    ├── AAPLViewController.m
    ├── AppKit/
    │   ├── AAPLNSView.h
    │   └── AAPLNSView.m
    ├── UIKit/
    │   ├── AAPLUIView.h
    │   └── AAPLUIView.m
    └── WindowSceneDelegate.h

Structure observations

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

Overall architecture

flowchart LR
    N1["main"]
    N2["AAPLViewController"]
    N3["AAPLRenderer"]
    N4["Metal APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

Application/main.m:18 — architecture anchor

#if defined(TARGET_IOS) || defined(TARGET_TVOS)
int main(int argc, char * argv[]) {

    @autoreleasepool {
        return UIApplicationMain(argc, argv, nil, NSStringFromClass([AAPLAppDelegate class]));
    }
}
#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
    AAPLView o-- CAMetalLayer : metalLayer
    AAPLView o-- BOOL : paused
    AAPLView o-- id : delegate
    WindowSceneDelegate o-- UIWindow : window

Ownership evidence

Application/AAPLView.h:34 — stored dependency or nearest verified ownership anchor

@interface AAPLView : NSView <CALayerDelegate>
// ...
@property (nonatomic, nonnull, readonly) CAMetalLayer *metalLayer;
// ...
@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

Application/AAPLView.h:19 — representative type boundary

@protocol AAPLViewDelegate <NSObject>

- (void)drawableResize:(CGSize)size;

- (void)renderToMetalLayer:(nonnull CAMetalLayer *)metalLayer;

@end

The source explicitly defines local protocol relationships: AAPLViewController → AAPLViewDelegate.

Access control

Reference code

Application/AAPLView.h:34 — representative boundary

@interface AAPLView : NSView <CALayerDelegate>
// ...
@property (nonatomic, nonnull, readonly) CAMetalLayer *metalLayer;
// ...
@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 AAPLRenderer
    participant _commandQueue
    participant metalLayer
    participant commandBuffer
    participant renderEncoder
    AAPLRenderer->>_commandQueue: commandBuffer()
    AAPLRenderer->>metalLayer: nextDrawable()
    AAPLRenderer->>commandBuffer: renderCommandEncoderWithDescriptor()
    AAPLRenderer->>renderEncoder: setRenderPipelineState()
    AAPLRenderer->>renderEncoder: setVertexBuffer()
    AAPLRenderer->>renderEncoder: setVertexBytes()
    AAPLRenderer->>commandBuffer: presentDrawable()
    AAPLRenderer->>commandBuffer: commit()

Reference code

Renderer/AAPLRenderer.m:172 — renderToMetalLayer()

- (void)renderToMetalLayer:(nonnull CAMetalLayer*)metalLayer
{
    // ...
    _frameNum++;
    id <MTLCommandBuffer> commandBuffer = [_commandQueue commandBuffer];
    id<CAMetalDrawable> currentDrawable = [metalLayer nextDrawable];
    if(!currentDrawable)
    {
        return;
    }
    _drawableRenderDescriptor.colorAttachments[0].texture = currentDrawable.texture;
    id <MTLRenderCommandEncoder> renderEncoder =
        [commandBuffer renderCommandEncoderWithDescriptor:_drawableRenderDescriptor];
    [renderEncoder setRenderPipelineState:_pipelineState];
    [renderEncoder setVertexBuffer:_vertices
                            offset:0
                           atIndex:AAPLVertexInputIndexVertices ];
    {
        AAPLUniforms uniforms;
#if ANIMATION_RENDERING
        uniforms.scale = 0.5 + (1.0 + 0.5 * sin(_frameNum * 0.1));
#else
        uniforms.scale = 1.0;
#endif
        uniforms.viewportSize = _viewportSize;
        [renderEncoder setVertexBytes:&uniforms
                               length:sizeof(uniforms)
                              atIndex:AAPLVertexInputIndexUniforms ];
    }
    [renderEncoder drawPrimitives:MTLPrimitiveTypeTriangle vertexStart:0 vertexCount:6];
    [renderEncoder endEncoding];
    [commandBuffer presentDrawable:currentDrawable];
    [commandBuffer commit];
}

Naming conventions

• Types: Controller: AAPLViewController; Delegate: AAPLAppDelegate, AAPLViewDelegate, WindowSceneDelegate; Renderer: AAPLRenderer; View: AAPLNSView, AAPLUIView, AAPLView.
• Protocols: AAPLViewDelegate.
• Methods: drawableResize, renderToMetalLayer, initCommon, resizeDrawable, stopRenderLoop, render, application, applicationShouldTerminateAfterLastWindowClosed.
• Files: Application/AAPLAppDelegate.h, Application/AAPLView.h, Application/AAPLAppDelegate.m, Application/AAPLView.m, Application/AAPLViewController.h, Application/AAPLViewController.m.

Architecture takeaways

• main is the main source-visible entry or composition anchor for this sample.
• Framework work reaches Metal, UIKit, QuartzCore, Cocoa 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