export default /* glsl */`
float roughnessFactor = roughness;
#ifdef USE_ROUGHNESSMAP
vec4 texelRoughness = texture2D( roughnessMap, vRoughnessMapUv );
// reads channel G, compatible with a combined OcclusionRoughnessMetallic (RGB) texture
roughnessFactor *= texelRoughness.g;
#endif
`;