Streaming large images with Metal sparse textures

At a glance

Project structure

Source bundle/
├── Renderer/
│   ├── AAPLRenderer.m
│   └── Shaders/
│       ├── AAPLShaders.metal
│       └── AAPLShaderTypes.h
└── Application/
    ├── AAPLViewController.m
    ├── main.m
    ├── WindowSceneDelegate.m
    ├── AAPLAppDelegate.h
    ├── AAPLAppDelegate.m
    └── AAPLViewController.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["sparse-texture residency manager"]
    N4["tile mapping and sampled rendering"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

Renderer/AAPLRenderer.m:310 — asynchronous sparse-residency update

    dispatch_async(_dispatch_queue, ^{
        // Process the sparse texture access counters, and map and blit tiles.
        [self->_sparseTexture update:self->_currentBufferIndex];
    });

Interpretation

This is the dominant control/data path: platform code composes AAPLRenderer; that object controls sparse-texture residency manager; GPU-visible work ends in tile mapping and sampled rendering. 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:41 — AAPLViewController creates and stores _renderer

@implementation AAPLViewController
// ...
    _renderer = [[AAPLRenderer alloc] initWithMetalKitView:_mtkView];
// ...
@end

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/Shaders/AAPLShaders.metal:60 — representative GPU entry/helper

fragment half4 forwardFragment(FragmentIn in [[stage_in]],
                               texture2d<half, access::sample> baseColorTexture [[texture(AAPLTextureIndexBaseColor)]],
                               constant SampleParams& sample                    [[buffer(AAPLBufferIndexSampleParams)]])
{
    // ...
}

Design patterns

Naming conventions

• Role suffixes make ownership visible: AAPLViewController, AAPLRenderer, AAPLAppDelegate, WindowSceneDelegate.
• Method names describe setup or encoding actions: application, applicationDidFinishLaunching, applicationWillTerminate, applicationShouldTerminateAfterLastWindowClosed, viewDidLoad, optionsChanged, mtkView.
• Shader entry points use stage/operation names: forwardFragment, forwardPlaneVertex, forwardWithSparseTextureFragment, debugSparseTextureQuadVertex, debugSparseTextureQuadFragment.
• 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 sparse-texture residency manager.
• Treat tile mapping and sampled rendering 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