three.js/src/renderers/shaders/ShaderChunk/defaultnormal_vertex.glsl.js

export default /* glsl */`
vec3 transformedNormal = objectNormal;

#ifdef USE_INSTANCING

	transformedNormal = mat3( instanceMatrix ) * transformedNormal;

#endif

transformedNormal = normalMatrix * transformedNormal;

#ifdef FLIP_SIDED

	transformedNormal = - transformedNormal;

#endif

#ifdef USE_TANGENT

	vec3 transformedTangent = ( modelViewMatrix * vec4( objectTangent, 0.0 ) ).xyz;

	#ifdef FLIP_SIDED

		transformedTangent = - transformedTangent;

	#endif

#endif
`;