Accelerating ray tracing and motion blur using Metal

At a glance

Project structure

Source bundle/
├── Application/
│   ├── ViewController.mm
│   ├── main.m
│   ├── AppDelegate.h
│   └── AppDelegate.m
└── Renderer/
    ├── Shaders.metal
    ├── Renderer.mm
    ├── Scene.mm
    ├── ShaderTypes.h
    └── Scene.h

Structure observations

• The entry/composition boundary and renderer or operation boundary are separate in the source; Renderer 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["ViewController"]
    N2["Renderer"]
    N3["motion acceleration structures"]
    N4["ray-tracing compute kernel"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

Application/ViewController.mm:60 — feature handoff or setup anchor

    Scene *scene = [Scene newMotionBlurSceneWithDevice:_view.device
                                    usePrimitiveMotion:usePrimitiveMotion];

    _renderer = [[Renderer alloc] initWithDevice:_view.device
                                           scene:scene
                              usePrimitiveMotion:usePrimitiveMotion];

    [_renderer mtkView:_view drawableSizeWillChange:_view.bounds.size];

Interpretation

This is the dominant control/data path: platform code composes Renderer; that object controls motion acceleration structures; GPU-visible work ends in ray-tracing compute kernel. The arrows summarize responsibility transfer, not a claim that every node directly calls the next.

Ownership and state

classDiagram
    ViewController *-- Renderer : _renderer

Ownership evidence

Application/ViewController.mm:63 — ViewController creates and stores _renderer

@implementation ViewController
// ...
    _renderer = [[Renderer alloc] initWithDevice:_view.device
                                           scene:scene
                              usePrimitiveMotion:usePrimitiveMotion];
// ...
@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.metal:169 — representative GPU entry/helper

kernel void raytracingKernel(uint2 tid [[thread_position_in_grid]],
                             constant FrameData & frameData,
                             texture2d<unsigned int> randomTex,
                             texture2d<float> prevTex,
                             texture2d<float, access::write> dstTex,
                             device MeshResources *resources,
                             device MTLAccelerationStructureMotionInstanceDescriptor *instances,
                             device AreaLight *areaLights,
                             accelerationStructureType accelerationStructure)
{
    // ...
}

Design patterns

Naming conventions

• Role suffixes make ownership visible: ViewController, Renderer, Scene, AppDelegate, WindowSceneDelegate.
• Method names describe setup or encoding actions: init, initWithDevice, uploadToBuffers, resourcesStride, encodeResourcesToBuffer, markResourcesAsUsedWithEncoder, addCubeWithFaces.
• Shader entry points use stage/operation names: raytracingKernel, copyVertex, copyFragment.
• Names favor concrete domain roles and target-local types; no broad public library namespace is introduced.

Architecture takeaways

• Keep ViewController focused on composition; Renderer is the owner of motion acceleration structures.
• Treat ray-tracing compute kernel as a separate execution/compilation boundary with explicit resource and data-layout contracts.
• The verified ownership edge is ViewController → _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