bigdatascreen/public/archive/static/js/jsm/utils/SceneUtils.js

import {
	Group,
	Mesh,
	BufferAttribute,
	BufferGeometry
} from 'three';

import { mergeGroups } from './BufferGeometryUtils.js';

function createMeshesFromInstancedMesh( instancedMesh ) {

	const group = new Group();

	const count = instancedMesh.count;
	const geometry = instancedMesh.geometry;
	const material = instancedMesh.material;

	for ( let i = 0; i < count; i ++ ) {

		const mesh = new Mesh( geometry, material );

		instancedMesh.getMatrixAt( i, mesh.matrix );
		mesh.matrix.decompose( mesh.position, mesh.quaternion, mesh.scale );

		group.add( mesh );

	}

	group.copy( instancedMesh );
	group.updateMatrixWorld(); // ensure correct world matrices of meshes

	return group;

}

function createMeshesFromMultiMaterialMesh( mesh ) {

	if ( Array.isArray( mesh.material ) === false ) {

		console.warn( 'THREE.SceneUtils.createMeshesFromMultiMaterialMesh(): The given mesh has no multiple materials.' );
		return mesh;

	}

	const object = new Group();
	object.copy( mesh );

	// merge groups (which automatically sorts them)

	const geometry = mergeGroups( mesh.geometry );

	const index = geometry.index;
	const groups = geometry.groups;
	const attributeNames = Object.keys( geometry.attributes );

	// create a mesh for each group by extracting the buffer data into a new geometry

	for ( let i = 0; i < groups.length; i ++ ) {

		const group = groups[ i ];

		const start = group.start;
		const end = start + group.count;

		const newGeometry = new BufferGeometry();
		const newMaterial = mesh.material[ group.materialIndex ];

		// process all buffer attributes

		for ( let j = 0; j < attributeNames.length; j ++ ) {

			const name = attributeNames[ j ];
			const attribute = geometry.attributes[ name ];
			const itemSize = attribute.itemSize;

			const newLength = group.count * itemSize;
			const type = attribute.array.constructor;

			const newArray = new type( newLength );
			const newAttribute = new BufferAttribute( newArray, itemSize );

			for ( let k = start, n = 0; k < end; k ++, n ++ ) {

				const ind = index.getX( k );

				if ( itemSize >= 1 ) newAttribute.setX( n, attribute.getX( ind ) );
				if ( itemSize >= 2 ) newAttribute.setY( n, attribute.getY( ind ) );
				if ( itemSize >= 3 ) newAttribute.setZ( n, attribute.getZ( ind ) );
				if ( itemSize >= 4 ) newAttribute.setW( n, attribute.getW( ind ) );

			}


			newGeometry.setAttribute( name, newAttribute );

		}

		const newMesh = new Mesh( newGeometry, newMaterial );
		object.add( newMesh );

	}

	return object;

}

function createMultiMaterialObject( geometry, materials ) {

	const group = new Group();

	for ( let i = 0, l = materials.length; i < l; i ++ ) {

		group.add( new Mesh( geometry, materials[ i ] ) );

	}

	return group;

}

export {
	createMeshesFromInstancedMesh,
	createMeshesFromMultiMaterialMesh,
	createMultiMaterialObject
};