Merge threejs GLTF/GLB geometries

mergeGeometries.ts

import { BufferGeometryUtils } from 'three/examples/jsm/utils/BufferGeometryUtils';
import { GLTFExporter } from 'three/examples/jsm/exporters/GLTFExporter';
import { BufferGeometry, getMesh, LoadGLTF, Material, Mesh, MeshBasicMaterial } from '@milk-ecs/three';
import { Blob, FileReader } from 'vblob';
import { writeFileSync } from 'fs';

// Some hacks to get GLTFExporter working in nodejs
global.window = global;
global.Blob = Blob;
global.FileReader = FileReader;
global.document = {
	createElement: nodeName => {
		if (nodeName !== 'canvas') throw new Error(`Cannot create node ${nodeName}`);
	}
};

const run = async () => {
	const forest = await LoadGLTF('assets/golf/maps/forest.glb');

	const materials = new Map<string, Material>();
	const mats: Material[] = [];
	const geometries: BufferGeometry[] = [];

	forest.scene.updateMatrixWorld(true);

	forest.scene.traverse(m => {
		if (m instanceof Mesh) {
			// Dedupe materials
			if (!materials.has(m.material.name)) {
				materials.set(m.material.name, m.material);
			}
			mats.push(materials.get(m.material.name) as Material);

			// Bake position into geometry
			// We need to clone it so children don't get matrixWorld applied multiple times.
			const geom = m.geometry.clone() as BufferGeometry;
			geom.applyMatrix4(m.matrixWorld);

			geometries.push(geom);
		}
	});

	let geometry = BufferGeometryUtils.mergeBufferGeometries(geometries, true);
	geometry = BufferGeometryUtils.mergeVertices(geometry);

	const mesh = new Mesh(geometry, mats);

	const exporter = new GLTFExporter();
	const options = {
		trs: false,
		onlyVisible: false,
		truncateDrawRange: false,
		binary: true,
		maxTextureSize: 4096
	};

	exporter.parse(
		mesh,
		data => {
			console.log(data);
			writeFileSync('test.glb', Buffer.from(data as ArrayBuffer));
		},
		options
	);
};

run();