Customizing shaders using function pointers and stitching

At a glance

Project structure

Source bundle/
├── Application/
│   ├── main.m
│   ├── AAPLAppDelegate.m
│   ├── AAPLAppDelegate.h
│   ├── iOS/
│   │   ├── AAPLSplitViewController.m
│   │   └── AAPLSplitViewController.h
│   ├── AAPLConfigurationViewController.h
│   ├── AAPLConfigurationViewController.m
│   ├── AAPLRenderViewController.h
│   ├── AAPLRenderViewController.m
│   ├── WindowSceneDelegate.h
│   └── WindowSceneDelegate.m
└── Renderer/
    └── AAPLRenderer.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 7 project/configuration file(s) and 8 source declaration(s).

Overall architecture

flowchart LR
    N1["main"]
    N2["AAPLConfigurationViewController"]
    N3["AAPLRenderer"]
    N4["metal_stdlib APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

Application/main.m:17 — architecture anchor

#if defined(TARGET_IOS)
int main(int argc, char * argv[]) {
    // ...
#error No simulator support for Metal API for this SDK version. Build for a device instead.
    // ...
}
#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
    AAPLAppDelegate o-- UIWindow : window
    AAPLConfigurationViewController o-- AAPLRenderViewController : renderViewController
    WindowSceneDelegate o-- UIWindow : window

Ownership evidence

Application/AAPLAppDelegate.m:13 — stored dependency or nearest verified ownership anchor

#if TARGET_IOS
@property (nonatomic, strong) UIWindow *window;
#endif

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/AAPLAppDelegate.m:12 — representative type boundary

#if TARGET_IOS
@interface AAPLWindowSceneDelegate : UIResponder <UIWindowSceneDelegate>
@property (nonatomic, strong) UIWindow *window;
@end
#endif

No local protocol conformance is claimed as protocol-oriented design; external framework conformances are listed only as dependencies.

Access control

Reference code

Application/AAPLAppDelegate.h:21 — representative boundary

#if !defined(TARGET_IOS)
@property (strong, nonatomic) PlatformWindow *window;
#endif

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 NSString
    participant renderEncoder
    participant commandBuffer
    AAPLRenderer->>_commandQueue: commandBuffer()
    AAPLRenderer->>NSString: stringWithFormat()
    AAPLRenderer->>renderEncoder: pushDebugGroup()
    AAPLRenderer->>renderEncoder: setRenderPipelineState()
    AAPLRenderer->>renderEncoder: setVertexBytes()
    AAPLRenderer->>renderEncoder: setVertexBytes()
    AAPLRenderer->>commandBuffer: presentDrawable()
    AAPLRenderer->>commandBuffer: commit()

Reference code

Renderer/AAPLRenderer.m:371 — drawInMTKView()

@implementation AAPLRenderer
// ...
        [commandBuffer commit];
// ...
@end

Naming conventions

• Types: Controller: AAPLConfigurationViewController, AAPLRenderViewController, AAPLSplitViewController; Delegate: AAPLAppDelegate, AAPLWindowSceneDelegate, WindowSceneDelegate; Renderer: AAPLRenderer.
• Protocols: no local protocol declaration in the scanned source.
• Methods: scene, sceneDidDisconnect, application, applicationShouldTerminateAfterLastWindowClosed, viewDidLoad, selectVisualizationType, selectOperation, selectIterations.
• Files: Application/AAPLAppDelegate.m, Application/AAPLAppDelegate.h, Application/iOS/AAPLSplitViewController.m, Application/AAPLConfigurationViewController.h, Application/AAPLConfigurationViewController.m, Application/AAPLRenderViewController.h.

Architecture takeaways

• main is the main source-visible entry or composition anchor for this sample.
• Framework work reaches UIKit, metal_stdlib, Cocoa, 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.
• The source does not justify labeling the design protocol-oriented.

Source map

• Official Apple documentation