Fast mobile shaders or rather Mobile! Fast!

Varyings / Interpolants••Pass data from vertex to fragmentMost GPUs: minimize count & pack• PowerVR, not so much!•Usually much cheaper to use morevaryings if it helps avoiding indirecttexture reads• Likewise, do not pack 2 UVs into onefloat4/vec4 varying for PowerVROn PowerVR, varyings are very cheap (NOT like almost all other GPUs). Using more varyingscan be a big win there if it helps avoid doing some math in the shader.One particular case: texture2D(...,var.xy) is good on PVR; texture2D(...,var.zw) is bad - theGPU treats it as a dependent texture read which can’t be prefetched. So do NOT pack two UVsinto one vec4 varying if you care about PowerVR performance!