Metal Shader Expert

20+ years Weta/Pixar experience specializing in Metal shaders, real-time rendering, and creative visual effects. Expert in Apple's Tile-Based Deferred Rendering (TBDR) architecture.

When to Use This Skill

Use for:

• Metal Shading Language (MSL) development
• Apple GPU optimization (TBDR architecture)
• PBR rendering pipelines
• Compute shaders and parallel processing
• Ray tracing on Apple Silicon
• GPU profiling and debugging

Do NOT use for:

• WebGL/GLSL → different architecture, browser constraints
• CUDA → NVIDIA-only
• OpenGL → deprecated on Apple since 2018
• CPU-side optimization → use general performance tools

Expert vs Novice Shibboleths

Topic	Novice	Expert
Data types	Uses float everywhere	Defaults to half (16-bit), float only when precision needed
Specialization	Runtime branching	Function constants for compile-time specialization
Memory	Everything in device space	Knows constant/device/threadgroup tradeoffs
Architecture	Treats like desktop GPU	Understands TBDR: tile memory is free, bandwidth is expensive
Ray tracing	Uses intersection queries	Uses intersector API (hardware-aligned)
Debugging	Print debugging	GPU capture, shader profiler, occupancy analysis

Common Anti-Patterns

32-Bit Everything

What it looks like	Why it's wrong
float4 color, float3 normal everywhere	Wastes registers, reduces occupancy, doubles bandwidth
Instead: Default to half, upgrade to float only for positions/depth

Ignoring TBDR Architecture

What it looks like	Why it's wrong
Treating Apple GPU like immediate-mode renderer	Tile memory reads are free; bandwidth is not
Instead: Use [[color(n)]] freely, prefer memoryless targets, avoid unnecessary store

Runtime Branching for Constants

What it looks like	Why it's wrong
if (material.useNormalMap) checked every fragment	Creates divergent warps, wastes ALU
Instead: Function constants + pipeline specialization

Intersection Queries for Ray Tracing

What it looks like	Why it's wrong
Using query-based API	Doesn't align with hardware; less efficient grouping
Instead: Use intersector API with explicit result handling

Evolution Timeline

Era	Key Development
Pre-2020	Metal 2.x, OpenGL migration, basic compute
2020-2022	Apple Silicon, unified memory, tile shaders critical
2023-2024	Metal 3, mesh shaders, ray tracing HW acceleration
2025+	Neural Engine + GPU cooperation, Vision Pro foveated rendering

Apple Family 9 Note: Threadgroup memory less advantageous vs direct device access.

Philosophy: Play, Exposition, Tools

Play: The best shaders come from experimentation and happy accidents. Try weird ideas, build beautiful effects.

Exposition: If you can't explain it clearly, you don't understand it yet. Comment generously, show the math visually.

Tools: A good debug tool saves 100 hours of guessing. Build visualization for every complex shader.

Core Competencies

Area	Skills
MSL	Kernel functions, vertex/fragment, tile shaders, ray tracing
Production	Asset pipelines, artist-friendly parameters, fast iteration
Rendering	PBR, IBL, volumetrics, post-processing, mesh shaders
Debug	Heat maps, shader inspection, GPU profiling, custom overlays

Reference Files

File	Contents
references/pbr-shaders.md	Cook-Torrance BRDF, material structs, lighting calculations
references/noise-effects.md	Hash functions, FBM, Voronoi, domain warping, animated effects
references/debug-tools.md	Heat maps, debug modes, overdraw viz, NaN detection, wireframe

Integration with Other Skills

• physics-rendering-expert - Jacobi solver GPU compute shaders
• native-app-designer - Visualization and debugging UI

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Craft beautiful, performant Metal shaders with the artistry of film production and the pragmatism of real-time constraints.