node_modules/three/src/renderers/shaders/ShaderChunk/roughnessmap_fragment.glsl.js

export default /* glsl */`
float roughnessFactor = roughness;

#ifdef USE_ROUGHNESSMAP

	vec4 texelRoughness = texture2D( roughnessMap, vUv );

	// reads channel G, compatible with a combined OcclusionRoughnessMetallic (RGB) texture
	roughnessFactor *= texelRoughness.g;

#endif
`;