texture-packing-variant-stripping

Texture Packing and Shader Variant Stripping for Unity Mobile

TRIGGER

Use this skill when the user is dealing with texture optimization, channel packing, shader variant bloat, build size, shader compilation time, or shader keyword management in Unity. Triggers include: "channel packing", "texture packing", "mask map", "MODS map", "RMA", "shader variants", "variant stripping", "multi_compile", "shader_feature", "build size", "shader keywords", "Always Included Shaders", "IPreprocessShaders", or complaints about slow shader compilation or large build sizes.

TEXTURE CHANNEL PACKING

Channel packing stores multiple grayscale maps in a single RGBA texture. This reduces both texture sample count and memory bandwidth — the primary bottleneck on mobile.

Standard URP Packing Convention

Mask Map (single RGBA texture):
  R = Metallic
  G = Occlusion (AO)
  B = Detail mask (or custom)
  A = Smoothness

Best Practices

1. Put the most visually important mask in the Green channel. Human vision is most sensitive to green, and most texture compression formats (ETC2, ASTC, DXT) allocate more bits to green.

2. Pack related data together. If metallic and smoothness are always sampled together, put them in the same texture.

3. Use linear color space (not sRGB) for packed mask textures. In Unity, uncheck "sRGB" in the texture import settings for any non-color data (roughness, AO, metallic, height).

4. One texture sample replaces four. Instead of:

   // BAD — 4 texture samples
   half metallic = SAMPLE_TEXTURE2D(_MetallicMap, sampler_MetallicMap, uv).r;
   half ao = SAMPLE_TEXTURE2D(_AOMap, sampler_AOMap, uv).r;
   half detail = SAMPLE_TEXTURE2D(_DetailMask, sampler_DetailMask, uv).r;
   half smooth = SAMPLE_TEXTURE2D(_SmoothnessMap, sampler_SmoothnessMap, uv).r;
   

   Use:

   // GOOD — 1 texture sample
   half4 masks = SAMPLE_TEXTURE2D(_MaskMap, sampler_MaskMap, uv);
   half metallic = masks.r;
   half ao = masks.g;
   half detail = masks.b;
   half smooth = masks.a;