Why my bone animation doesn't work when I change material?

Questions
,
1

Hi,

I have an issue with an animated GLTF model. GLTF loader import all the model’s materials as MeshStandardMaterial. As it is expensive, I wish to change some of them to MeshLambertMaterial. However, when I do it with a SkinnedMesh, the animation doesn’t work. I tried to set the material skinning and morphTargets to true, but it still doesn’t work.

How can I change the material of my SkinnedMesh, while keeping the animation ?

This is how my code looks like :

/// Material creation

var myLambertMaterial = new THREE.MeshLambertMaterial({
	color:0x00ff00,
	skinning:true,
	morphTargets:true,
	morphNormals:true
});

/// Material assignation

changeMaterial( importedModel );

function changeMaterial( obj ) {
	if ( obj.material ) {
		obj.material = myLambertMaterial;
	};
	if ( obj.children.length > 0 ) {
		obj.children.forEach( (child)=> {
			changeMaterial( child );
		});
	};
};
2

I don’t really understand why, but if I change my condition to this, it solves the problem :

function changeMaterial( obj ) {
	if ( obj.type == 'SkinnedMesh' /* I just checked for obj.material */  ) {
		obj.material = myLambertMaterial;
	};
	if ( obj.children.length > 0 ) {
		obj.children.forEach( (child)=> {
			changeMaterial( child );
		});
	};
};