Encoding indirect command buffers on the CPU

At a glance

Project structure

Source bundle/
├── Application/
│   ├── main.m
│   ├── AAPLAppDelegate.h
│   ├── AAPLAppDelegate.m
│   ├── AAPLViewController.h
│   ├── AAPLViewController.m
│   ├── WindowSceneDelegate.h
│   ├── WindowSceneDelegate.m
│   └── iOS/
│       └── Base.lproj/
│           └── Main.storyboard
└── Renderer/
    ├── AAPLRenderer.m
    ├── AAPLRenderer.h
    ├── AAPLShaders.metal
    └── AAPLShaderTypes.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 5 source declaration(s).

Overall architecture

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

Reference code

Application/main.m:18 — architecture anchor

#if defined(TARGET_IOS)
int main(int argc, char * argv[]) {
    // ...
#error This sample does not have simulator support and must be built for a device.
    // ...
}
#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

Ownership evidence

Application/WindowSceneDelegate.h:13 — stored dependency or nearest verified ownership anchor

@interface WindowSceneDelegate : UIResponder <UIWindowSceneDelegate>

@property (nonatomic, strong) UIWindow *window;

@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/AAPLAppDelegate.h:10 — representative type boundary

@interface AAPLAppDelegate : UIResponder <UIApplicationDelegate>

@end

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:13 — representative boundary

@interface WindowSceneDelegate : UIResponder <UIWindowSceneDelegate>

@property (nonatomic, strong) UIWindow *window;

@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 commandBuffer
    participant blitEncoder
    participant renderEncoder
    AAPLRenderer->>AAPLRenderer: updateState()
    AAPLRenderer->>_commandQueue: commandBuffer()
    AAPLRenderer->>commandBuffer: addCompletedHandler()
    AAPLRenderer->>commandBuffer: blitCommandEncoder()
    AAPLRenderer->>blitEncoder: sourceOffset()
    AAPLRenderer->>renderEncoder: setCullMode()
    AAPLRenderer->>commandBuffer: presentDrawable()
    AAPLRenderer->>commandBuffer: commit()

Reference code

Renderer/AAPLRenderer.m:397 — drawInMTKView()

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

Naming conventions

• Types: Controller: AAPLViewController; Delegate: AAPLAppDelegate, WindowSceneDelegate; Renderer: AAPLRenderer.
• Protocols: no local protocol declaration in the scanned source.
• Methods: initWithMetalKitView, newGearMeshWithNumTeeth, updateState, mtkView, drawInMTKView, application, viewDidLoad, scene.
• Files: Application/AAPLAppDelegate.h, Renderer/AAPLRenderer.m, Application/AAPLAppDelegate.m, Application/AAPLViewController.h, Application/AAPLViewController.m, Application/WindowSceneDelegate.h.

Architecture takeaways

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