Migrating OpenGL code to Metal

At a glance

Project structure

Source bundle/
├── Common/
│   ├── main.m
│   ├── AAPLAppDelegate.h
│   ├── AAPLMeshData.h
│   ├── AAPLAppDelegate.m
│   ├── WindowSceneDelegate.h
│   └── WindowSceneDelegate.m
├── Metal/
│   ├── AAPLMetalRenderer.m
│   ├── AAPLMetalRenderer.h
│   └── AAPLMetalViewController.h
└── OpenGL/
    ├── AAPLOpenGLRenderer.m
    ├── AAPLOpenGLViewController.h
    └── AAPLOpenGLViewController.m

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, Objective-C++.
• The verified tree contains 9 project/configuration file(s) and 14 source declaration(s).

Overall architecture

flowchart LR
    N1["main"]
    N2["AAPLMetalViewController"]
    N3["AAPLMetalRenderer"]
    N4["simd / OpenGLES APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

Common/main.m:19 — architecture anchor

#if defined(TARGET_IOS) || defined(TARGET_TVOS)
int main(int argc, char * argv[]) {
    // ...
#error Metal is not supported in this version of 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
    AAPLVertexData o-- uint32_t : indexData
    AAPLVertexData o-- NSUInteger : indexCount
    AAPLVertexData o-- NSURL : baseColorMapURL
    AAPLVertexData o-- AAPLVertexData : vertexData

Ownership evidence

Common/AAPLMeshData.h:22 — stored dependency or nearest verified ownership anchor

@interface AAPLSubmeshData : NSObject
// ...
@property (nonatomic, readonly, nonnull) uint32_t *indexData;
// ...
@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

Common/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

Common/AAPLMeshData.h:22 — representative boundary

@interface AAPLSubmeshData : NSObject
// ...
@property (nonatomic, readonly, nonnull) uint32_t *indexData;
// ...
@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

Naming conventions

• Types: Controller: AAPLMetalViewController, AAPLOpenGLViewController; Delegate: AAPLAppDelegate, WindowSceneDelegate; Renderer: AAPLMetalRenderer, AAPLOpenGLRenderer; View: AAPLOpenGLView.
• Protocols: no local protocol declaration in the scanned source.
• Methods: initWithURL, initWithMetalKitView, buildTempleObjects, buildReflectiveQuadObjects, updateFrameState, mtkView, drawInMTKView, initWithDefaultFBOName.
• Files: Common/AAPLAppDelegate.h, Common/AAPLMeshData.h, Metal/AAPLMetalRenderer.m, OpenGL/AAPLOpenGLRenderer.m, OpenGL/AAPLOpenGLViewController.h, OpenGL/AAPLOpenGLViewController.m.

Architecture takeaways

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