obj2gltf/lib/gltfToGlb.js

'use strict';
const Cesium = require('cesium');
const getJsonBufferPadded = require('./getJsonBufferPadded');

const defined = Cesium.defined;

module.exports = gltfToGlb;

/**
 * Convert a glTF to binary glTF.
 *
 * The glTF is expected to have a single buffer and all embedded resources stored in bufferViews.
 *
 * @param {Object} gltf The glTF asset.
 * @param {Buffer} binaryBuffer The binary buffer.
 * @returns {Buffer} The glb buffer.
 *
 * @private
 */
function gltfToGlb(gltf, binaryBuffer) {
    const buffer = gltf.buffers[0];
    if (defined(buffer.uri)) {
        binaryBuffer = Buffer.alloc(0);
    }

    // Create padded binary scene string
    const jsonBuffer = getJsonBufferPadded(gltf);

    // Allocate buffer (Global header) + (JSON chunk header) + (JSON chunk) + (Binary chunk header) + (Binary chunk)
    const glbLength = 12 + 8 + jsonBuffer.length + 8 + binaryBuffer.length;
    const glb = Buffer.alloc(glbLength);

    // Write binary glTF header (magic, version, length)
    let byteOffset = 0;
    glb.writeUInt32LE(0x46546C67, byteOffset);
    byteOffset += 4;
    glb.writeUInt32LE(2, byteOffset);
    byteOffset += 4;
    glb.writeUInt32LE(glbLength, byteOffset);
    byteOffset += 4;

    // Write JSON Chunk header (length, type)
    glb.writeUInt32LE(jsonBuffer.length, byteOffset);
    byteOffset += 4;
    glb.writeUInt32LE(0x4E4F534A, byteOffset); // JSON
    byteOffset += 4;

    // Write JSON Chunk
    jsonBuffer.copy(glb, byteOffset);
    byteOffset += jsonBuffer.length;

    // Write Binary Chunk header (length, type)
    glb.writeUInt32LE(binaryBuffer.length, byteOffset);
    byteOffset += 4;
    glb.writeUInt32LE(0x004E4942, byteOffset); // BIN
    byteOffset += 4;

    // Write Binary Chunk
    binaryBuffer.copy(glb, byteOffset);
    return glb;
}