third_party/skia/src/sksl/sksl_frag.sksl

// defines built-in interfaces supported by SkiaSL fragment shaders

// See "enum SpvBuiltIn_" in ./spirv.h
layout(builtin=15) in float4 sk_FragCoord;
layout(builtin=17) in bool sk_Clockwise;  // Similar to gl_FrontFacing, but defined in device space.

layout(location=0,index=0,builtin=10001) out half4 sk_FragColor;
layout(builtin=10008) half4 sk_LastFragColor;
layout(builtin=10012) out half4 sk_SecondaryFragColor;