Rendering reflections in real time using ray tracing

At a glance

Project structure

Source bundle/
├── Application/
│   ├── main.m
│   ├── AAPLAppDelegate.h
│   ├── AAPLAppDelegate.m
│   ├── WindowSceneDelegate.h
│   ├── WindowSceneDelegate.m
│   ├── iOS/
│   │   ├── AAPLViewController.h
│   │   └── AAPLViewController.m
│   └── macOS/
│       ├── AAPLViewController.h
│       └── AAPLViewController.m
└── Renderer/
    ├── AAPLRenderer.m
    ├── AAPLArgumentBufferTypes.h
    └── AAPLShaders.metal

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 8 project/configuration file(s) and 23 source declaration(s).

Overall architecture

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

Reference code

Application/main.m:19 — architecture anchor

#if defined(TARGET_IOS)
int main(int argc, char * argv[]) {
    // ...
#error This sample does not support the iOS Simulator
    // ...
}
#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
    AAPLViewController o-- UIActivityIndicatorView : loadingSpinner
    AAPLViewController o-- UILabel : loadingLabel
    AAPLViewController o-- NSSegmentedControl : renderModeControl

Ownership evidence

Application/WindowSceneDelegate.h:17 — stored dependency or nearest verified ownership anchor

#if TARGET_OS_IOS || TARGET_OS_TV
@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.h:11 — representative type boundary

#if TARGET_IOS
@interface AAPLAppDelegate : UIResponder <UIApplicationDelegate>

@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/WindowSceneDelegate.h:17 — representative boundary

#if TARGET_OS_IOS || TARGET_OS_TV
@property (nonatomic, strong) UIWindow *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 NSMutableArray
    participant _device
    participant _commandQueue
    participant cmd
    participant heap
    participant enc
    AAPLRenderer->>NSMutableArray: arrayWithCapacity()
    AAPLRenderer->>_device: newBufferWithLength()
    AAPLRenderer->>_commandQueue: commandBuffer()
    AAPLRenderer->>cmd: accelerationStructureCommandEncoder()
    AAPLRenderer->>_device: heapAccelerationStructureSizeAndAlignWithDescriptor()
    AAPLRenderer->>heap: newAccelerationStructureWithSize()
    AAPLRenderer->>enc: buildAccelerationStructure()
    AAPLRenderer->>cmd: commit()

Reference code

Renderer/AAPLRenderer.m:828 — allocateAndBuildAccelerationStructuresWithDescriptors()

- (NSArray<id<MTLAccelerationStructure>> *)allocateAndBuildAccelerationStructuresWithDescriptors:(NSArray<MTLAccelerationStructureDescriptor *>*)descriptors
                                                                                            heap:(id<MTLHeap>)heap
                                                                            maxScratchBufferSize:(size_t)maxScratchSize
                                                                                     signalEvent:(id<MTLEvent>)event NS_AVAILABLE(13,16)
{
    NSAssert( heap, @"Heap argument is required" );

    NSMutableArray< id<MTLAccelerationStructure> >* accelStructures = [NSMutableArray arrayWithCapacity:descriptors.count];

    id<MTLBuffer> scratch = [_device newBufferWithLength:maxScratchSize options:MTLResourceStorageModePrivate];
    id<MTLCommandBuffer> cmd = [_commandQueue commandBuffer];
    id<MTLAccelerationStructureCommandEncoder> enc = [cmd accelerationStructureCommandEncoder];

    for ( MTLPrimitiveAccelerationStructureDescriptor* descriptor in descriptors )
    {
        MTLSizeAndAlign sizes = [_device heapAccelerationStructureSizeAndAlignWithDescriptor:descriptor];
        id<MTLAccelerationStructure> accelStructure = [heap newAccelerationStructureWithSize:sizes.size];
        [enc buildAccelerationStructure:accelStructure descriptor:descriptor scratchBuffer:scratch scratchBufferOffset:0];
        [accelStructures addObject:accelStructure];
    }

    [enc endEncoding];
    [cmd encodeSignalEvent:event value:kPrimitiveAccelerationStructureBuild];
    [cmd commit];

    return accelStructures;
}

Naming conventions

• Types: Controller: AAPLViewController; Delegate: AAPLAppDelegate, WindowSceneDelegate; Renderer: AAPLRenderer; Scene: Scene.
• Protocols: no local protocol declaration in the scanned source.
• Methods: initWithMetalKitView, resizeRTReflectionMapTo, loadMetalWithView, loadAssets, argumentDescriptorWithIndex, buildSceneArgumentBufferFromReflectionFunction, newArgumentEncoderWithBufferIndex, newResidencySetWithLabel.
• Files: Application/AAPLAppDelegate.h, Renderer/AAPLRenderer.m, Application/AAPLAppDelegate.m, Application/WindowSceneDelegate.h, Application/WindowSceneDelegate.m, Application/iOS/AAPLViewController.h.

Architecture takeaways

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

Source map

• Official Apple documentation