copy method
Copy the parameters from the passed material into this material.
Implementation
@override
MeshStandardMaterial copy(Material source) {
super.copy(source);
final newSource = source as GLTFMeshStandardSGMaterial;
specularMap = newSource.specularMap;
specular!.setFrom(newSource.specular!);
glossinessMap = newSource.glossinessMap;
glossiness = newSource.glossiness;
// delete this.metalness;
// delete this.roughness;
// delete this.metalnessMap;
// delete this.roughnessMap;
return this;
}