Sample code for generating a torus-shaped GLB from scratch using glTF Transform.

gen-torus.js

import { Document, NodeIO } from '@gltf-transform/core';

function createTorus(radius = 1, tube = 0.4, radialSegments = 12, tubularSegments = 48, arc = Math.PI * 2) {
	const indicesArray = [];
	const positionArray = [];
	const texcoordArray = [];

	const vertex = [0, 0, 0];

	// generate positions and uvs
	for (let j = 0; j <= radialSegments; j++) {
		for (let i = 0; i <= tubularSegments; i++) {
			const u = (i / tubularSegments) * arc;
			const v = (j / radialSegments) * Math.PI * 2;

			// position
			vertex[0] = (radius + tube * Math.cos(v)) * Math.cos(u);
			vertex[1] = (radius + tube * Math.cos(v)) * Math.sin(u);
			vertex[2] = tube * Math.sin(v);
			positionArray.push(vertex[0], vertex[1], vertex[2]);

			// uv
			texcoordArray.push(i / tubularSegments);
			texcoordArray.push(j / radialSegments);
		}
	}

	// generate indices
	for (let j = 1; j <= radialSegments; j++) {
		for (let i = 1; i <= tubularSegments; i++) {
			// indices

			const a = (tubularSegments + 1) * j + i - 1;
			const b = (tubularSegments + 1) * (j - 1) + i - 1;
			const c = (tubularSegments + 1) * (j - 1) + i;
			const d = (tubularSegments + 1) * j + i;

			// faces

			indicesArray.push(a, b, d);
			indicesArray.push(b, c, d);
		}
	}

	const document = new Document();
	const buffer = document.createBuffer();
	const material = document.createMaterial().setBaseColorHex(0x4285f4).setRoughnessFactor(1).setMetallicFactor(0);

	// indices and vertex attributes
	const indices = document
		.createAccessor()
		.setArray(new Uint16Array(indicesArray))
		.setType('SCALAR')
		.setBuffer(buffer);
	const position = document
		.createAccessor()
		.setArray(new Float32Array(positionArray))
		.setType('VEC3')
		.setBuffer(buffer);
	const texcoord = document
		.createAccessor()
		.setArray(new Float32Array(texcoordArray))
		.setType('VEC2')
		.setBuffer(buffer);

	const prim = document
		.createPrimitive()
		.setMaterial(material)
		.setIndices(indices)
		.setAttribute('POSITION', position)
		.setAttribute('TEXCOORD_0', texcoord);

	const mesh = document.createMesh('MyMesh').addPrimitive(prim);
	const node = document.createNode('MyNode').setMesh(mesh);
	const scene = document.createScene('MyScene').addChild(node);

	return document;
}

const document = createTorus();
const io = new NodeIO();
await io.write('./torus.glb', document);