README_METAL.md

METAL version

Metal support is currently highly experimental and very work in progress.

Porting Progress

• Animation
• Blend
• Color
  • Blend
  • Dither (not fully vetted / just spot checked)
  • Palette
  • Levels
  • Space
  • Tonemap
• Distort
• Draw - (not fully vetted / just spot checked)
• Filters
  • Gaussian Blur
  • Box 2d
• Generative (not fully vetted / just spot checked)
• Geometry
• Lighting
• Math - (not fully vetted / just spot checked)
• Morphological
• Sample
• Sampler
• SDF - (not fully vetted / just spot checked)
• Space

Porting Methodology

• dupe *.glsl files-> and rename them to *.msl
• find replace .glsl -> .msl and ensure you repeat the above for imports
• find replace vec2 -> float2
• find replace vec3 -> float3
• find replace vec4 -> float4
• find replace matN -> matrix<float, n, n>
• find replace in function argument keyword -> `` as metal doesn't have the in function keyword
• find inout and determine which thread local memory keyword should replace it, and make it a reference
• ensure const is only used within functions, constant must be used for global scoped constants

Things to look out for

• Metal does not have the same basic math functions signatures as GLSL. We are adding all the polyfill functions in the math/ folder.
• Texture precision and filtering.
  • Added SAMPLER_TYPE which specifies the texture precisions. Defaults to texture2d<float>
  • This means your texture definition must match the default float precision, or you will need to override SAMPLER_TYPE
  • Added SAMPLER which specifies the Metal sampler object. Defaults to sampler( min_filter::linear, mag_filter::linear )

Things not yet done

• gl_FragCoord compatibilty. Not sure if there is a nice way to make this work without end users annotating their root Metal shader entry point.
  • For now, use the function definitions which pass the [[position]] coords from your main shader.
• atan / atan2 compatibility. Need to see if there is a nice way to override the function signatures to match.