charleswiltgen iOS Graphics Router
You MUST use this skill for ANY GPU rendering, graphics programming, 3D content display, or display performance work.
When to Use
Use this router when:
- Porting OpenGL/OpenGL ES code to Metal
- Porting DirectX code to Metal
- Converting GLSL/HLSL shaders to Metal Shading Language
- Setting up MTKView or CAMetalLayer
- Debugging GPU rendering issues (black screen, wrong colors, crashes)
- Evaluating translation layers (MetalANGLE, MoltenVK)
- Optimizing GPU performance or fixing thermal throttling
- App stuck at 60fps on ProMotion device
- Configuring CADisplayLink or render loops
- Variable refresh rate display issues
- Displaying 3D content in a non-game SwiftUI app
- Building AR experiences with RealityKit
- Using RealityView or Model3D in SwiftUI
- Spatial computing or visionOS 3D content
Routing Logic
Metal Migration
Strategy decisions → /skill axiom-metal-migration
- Translation layer vs native rewrite decision
- Project assessment and migration planning
- Anti-patterns and common mistakes
- Pressure scenarios for deadline resistance
API reference & conversion → /skill axiom-metal-migration-ref
- GLSL → MSL shader conversion tables
- HLSL → MSL shader conversion tables
- GL/D3D API → Metal API equivalents
- MTKView setup, render pipelines, compute shaders
- Complete WWDC code examples
Diagnostics → /skill axiom-metal-migration-diag
- Black screen after porting
- Shader compilation errors
- Wrong colors or coordinate systems
- Performance regressions
- Time-cost analysis per diagnostic path
Display Performance
Frame rate & render loops → /skill axiom-display-performance
- App stuck at 60fps on ProMotion (120Hz) device
- MTKView or CADisplayLink configuration
- Variable refresh rate optimization
- System caps (Low Power Mode, Limit Frame Rate, Thermal, Adaptive Power)
- Frame budget math (8.33ms for 120Hz)
- Measuring actual vs reported frame rate
RealityKit (Non-Game 3D Content)
For 3D content in non-game SwiftUI apps, AR experiences, and spatial computing, use the RealityKit skills. For game-specific RealityKit patterns, use the ios-games router instead.
Architecture, ECS, and best practices → /skill axiom-realitykit
- Entity-Component-System architecture
- SwiftUI integration: RealityView, Model3D, attachments
- AR on iOS: AnchorEntity types, SpatialTrackingSession
- Materials, physics, interaction
- Performance optimization
API reference → /skill axiom-realitykit-ref
- Complete component catalog
- RealityView and Model3D API
- Material system (PBR, Unlit, Occlusion, Custom)
- RealityRenderer (Metal integration)
Troubleshooting → /skill axiom-realitykit-diag
- Entity not visible, anchor not tracking
- Gesture not responding, performance issues
- Material problems, physics issues
Decision Tree
- Translation layer vs native rewrite? → metal-migration
- Porting / converting code to Metal? → metal-migration
- API reference / shader conversion tables? → metal-migration-ref
- MTKView / render pipeline setup? → metal-migration-ref
- Something broken after porting (black screen, wrong colors)? → metal-migration-diag
- Stuck at 60fps on ProMotion device? → display-performance
- CADisplayLink / variable refresh rate? → display-performance
- Frame rate not as expected? → display-performance
- Display a 3D model in SwiftUI? → axiom-realitykit
- Build an AR experience? → axiom-realitykit
- RealityView or Model3D setup? → axiom-realitykit-ref
- 3D content not visible or not tracking? → axiom-realitykit-diag
- Custom Metal rendering of RealityKit content? → axiom-realitykit-ref (RealityRenderer)
- Building a 3D game? → Use ios-games router instead
Anti-Rationalization
| Thought | Reality |
|---|---|
| "I'll just translate the shaders line by line" | GLSL→MSL has type, coordinate, and precision differences. metal-migration-ref has conversion tables. |
| "MetalANGLE will handle everything" | Translation layers have significant limitations for production. metal-migration evaluates the trade-offs. |
| "It's just a black screen, probably a simple bug" | Black screen has 6 distinct causes. metal-migration-diag diagnoses in 5 min vs 30+ min. |
| "My app runs at 60fps, that's fine" | ProMotion devices support 120Hz. display-performance configures the correct frame rate. |
| "I'll just use SceneKit for the 3D model" | SceneKit is soft-deprecated. RealityView and Model3D are the modern path. axiom-realitykit covers SwiftUI integration. |
| "I don't need ECS for one 3D model" | Model3D shows one model with zero ECS. RealityView scales to complex scenes. axiom-realitykit shows both paths. |
Critical Patterns
metal-migration:
- Translation layer (MetalANGLE) for quick demos
- Native Metal rewrite for production
- State management differences (GL stateful → Metal explicit)
- Coordinate system gotchas (Y-flip, NDC differences)
metal-migration-ref:
- Complete shader type mappings
- API equivalent tables
- MTKView vs CAMetalLayer decision
- Render pipeline setup patterns
metal-migration-diag:
- GPU Frame Capture workflow (2-5 min vs 30+ min guessing)
- Shader debugger for variable inspection
- Metal validation layer for API misuse
- Performance regression diagnosis
display-performance:
- MTKView defaults to 60fps (must set preferredFramesPerSecond = 120)
- CADisplayLink preferredFrameRateRange for explicit rate control
- System caps: Low Power Mode, Limit Frame Rate, Thermal, Adaptive Power (iOS 26)
- 8.33ms frame budget for 120Hz
- UIScreen.maximumFramesPerSecond lies; CADisplayLink tells truth
axiom-realitykit (non-game 3D):
- RealityView make/update closure pattern
- Model3D for simple model display
- AR anchoring with AnchorEntity
- Material selection (SimpleMaterial, PBR, Occlusion)
axiom-realitykit-ref (API):
- RealityRenderer for custom Metal rendering of RealityKit content
- Complete material property reference
- RealityView gesture integration
Example Invocations
User: "Should I use MetalANGLE or rewrite in native Metal?"
→ Invoke: /skill axiom-metal-migration
User: "I'm porting projectM from OpenGL ES to iOS"
→ Invoke: /skill axiom-metal-migration
User: "How do I convert this GLSL shader to Metal?"
→ Invoke: /skill axiom-metal-migration-ref
User: "Setting up MTKView for the first time"
→ Invoke: /skill axiom-metal-migration-ref
User: "My ported app shows a black screen"
→ Invoke: /skill axiom-metal-migration-diag
User: "Performance is worse after porting to Metal"
→ Invoke: /skill axiom-metal-migration-diag
User: "My app is stuck at 60fps on iPhone Pro"
→ Invoke: /skill axiom-display-performance
User: "How do I configure CADisplayLink for 120Hz?"
→ Invoke: /skill axiom-display-performance
User: "ProMotion not working in my Metal app"
→ Invoke: /skill axiom-display-performance
User: "How do I show a 3D model in my SwiftUI app?"
→ Invoke: /skill axiom-realitykit
User: "I need to display a USDZ model"
→ Invoke: /skill axiom-realitykit
User: "How do I set up RealityView?"
→ Invoke: /skill axiom-realitykit-ref
User: "My 3D model isn't showing in RealityView"
→ Invoke: /skill axiom-realitykit-diag
User: "How do I use RealityRenderer with Metal?"
→ Invoke: /skill axiom-realitykit-ref
User: "I need AR in my app"
→ Invoke: /skill axiom-realitykit