axiom-metal-migration-ref

# Metal Migration Reference

Complete reference for converting OpenGL/DirectX code to Metal.

## When to Use This Reference

Use this reference when:
- Converting GLSL shaders to Metal Shading Language (MSL)
- Converting HLSL shaders to MSL
- Looking up GL/D3D API equivalents in Metal
- Setting up MTKView or CAMetalLayer
- Building render pipelines
- Using Metal Shader Converter for DirectX

## Part 1: GLSL to MSL Conversion

### Type Mappings

| GLSL | MSL | Notes |
|------|-----|-------|
| `void` | `void` | |
| `bool` | `bool` | |
| `int` | `int` | 32-bit signed |
| `uint` | `uint` | 32-bit unsigned |
| `float` | `float` | 32-bit |
| `double` | N/A | Use `float` (no 64-bit float in MSL) |
| `vec2` | `float2` | |
| `vec3` | `float3` | |
| `vec4` | `float4` | |
| `ivec2` | `int2` | |
| `ivec3` | `int3` | |
| `ivec4` | `int4` | |
| `uvec2` | `uint2` | |
| `uvec3` | `uint3` | |
| `uvec4` | `uint4` | |
| `bvec2` | `bool2` | |
| `bvec3` | `bool3` | |
| `bvec4` | `bool4` | |
| `mat2` | `float2x2` | |
| `mat3` | `float3x3` | |
| `mat4` | `float4x4` | |
| `mat2x3` | `float2x3` | Columns x Rows |
| `mat3x4` | `float3x4` | |
| `sampler2D` | `texture2d<float>` + `sampler` | Separate in MSL |
| `sampler3D` | `texture3d<float>` + `sampler` | |
| `samplerCube` | `texturecube<float>` + `sampler` | |
| `sampler2DArray` | `texture2d_array<float>` + `sampler` | |
| `sampler2DShadow` | `depth2d<float>` + `sampler` | |

### Built-in Variable Mappings

| GLSL | MSL | Stage |
|------|-----|-------|
| `gl_Position` | Return `[[position]]` | Vertex |
| `gl_PointSize` | Return `[[point_size]]` | Vertex |
| `gl_VertexID` | `[[vertex_id]]` parameter | Vertex |
| `gl_InstanceID` | `[[instance_id]]` parameter | Vertex |
| `gl_FragCoord` | `[[position]]` parameter | Fragment |
| `gl_FrontFacing` | `[[front_facing]]` parameter | Fragment |
| `gl_PointCoord` | `[[point_coord]]` parameter | Fragment |
| `gl_FragDepth` | Return `[[depth(any)]]` | Fragment |
| `gl_SampleID` | `[[sample_id]]` paramet