BufferGeometryUtils: Add "deinterleaveAttribute", "deinterleaveGeometry" functions (#23814)

* Add "deinterleaveAttribute", "deinterleaveGeometry" functions

* add morph targets to deinterleaveGeometry function

* ensure we don't create duplicate attributes

examples/jsm/utils/BufferGeometryUtils.js

@@ -437,6 +437,97 @@ function interleaveAttributes( attributes ) {
 
 }
 
+// returns a new, non-interleaved version of the provided attribute
+export function deinterleaveAttribute( attribute ) {
+
+	const cons = attribute.data.array.constructor;
+	const count = attribute.count;
+	const itemSize = attribute.itemSize;
+	const normalized = attribute.normalized;
+
+	const array = new cons( count * itemSize );
+	let newAttribute;
+	if ( attribute.isInstancedInterleavedBufferAttribute ) {
+
+		newAttribute = new InstancedBufferAttribute( array, itemSize, normalized, attribute.meshPerAttribute );
+
+	} else {
+
+		newAttribute = new BufferAttribute( array, itemSize, normalized );
+
+	}
+
+	for ( let i = 0; i < count; i ++ ) {
+
+		newAttribute.setX( i, attribute.getX( i ) );
+
+		if ( itemSize >= 2 ) {
+
+			newAttribute.setY( i, attribute.getY( i ) );
+
+		}
+
+		if ( itemSize >= 3 ) {
+
+			newAttribute.setZ( i, attribute.getZ( i ) );
+
+		}
+
+		if ( itemSize >= 4 ) {
+
+			newAttribute.setW( i, attribute.getW( i ) );
+
+		}
+
+	}
+
+	return newAttribute;
+
+}
+
+// deinterleaves all attributes on the geometry
+export function deinterleaveGeometry( geometry ) {
+
+	const attributes = geometry.attributes;
+	const morphTargets = geometry.morphTargets;
+	const attrMap = new Map();
+
+	for ( const key in attributes ) {
+
+		const attr = attributes[ key ];
+		if ( attr.isInterleavedBufferAttribute ) {
+
+			if ( ! attrMap.has( attr ) ) {
+
+				attrMap.set( attr, deinterleaveAttribute( attr ) );
+
+			}
+
+			attributes[ key ] = attrMap.get( attr );
+
+		}
+
+	}
+
+	for ( const key in morphTargets ) {
+
+		const attr = morphTargets[ key ];
+		if ( attr.isInterleavedBufferAttribute ) {
+
+			if ( ! attrMap.has( attr ) ) {
+
+				attrMap.set( attr, deinterleaveAttribute( attr ) );
+
+			}
+
+			morphTargets[ key ] = attrMap.get( attr );
+
+		}
+
+	}
+
+}
+
 /**
  * @param {Array<BufferGeometry>} geometry
  * @return {number}