obj2gltf/lib/gltfToGlb.js

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2017-07-19 17:56:24 -04:00
'use strict';
var Cesium = require('cesium');
var getJsonBufferPadded = require('./getJsonBufferPadded');
var isDataUri = Cesium.isDataUri;
module.exports = gltfToGlb;
/**
* Convert a glTF to binary glTF.
*
* The glTF is expected to have all resources embedded as bufferViews and a single buffer whose content is stored in a data uri.
*
2017-07-19 17:56:24 -04:00
* @param {Object} gltf A javascript object containing a glTF asset.
* @returns {Promise} A promise that resolves to a buffer containing the binary glTF.
*
* @private
*/
function gltfToGlb(gltf) {
var buffer = gltf.buffers[0];
var binaryBuffer;
if (isDataUri(buffer.uri)) {
binaryBuffer = dataUriToBuffer(buffer.uri);
delete buffer.uri;
} else {
binaryBuffer = Buffer.alloc(0);
}
// Create padded binary scene string
var jsonBuffer = getJsonBufferPadded(gltf);
// Allocate buffer (Global header) + (JSON chunk header) + (JSON chunk) + (Binary chunk header) + (Binary chunk)
var glbLength = 12 + 8 + jsonBuffer.length + 8 + binaryBuffer.length;
var glb = Buffer.alloc(glbLength);
// Write binary glTF header (magic, version, length)
var 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;
}
function dataUriToBuffer(dataUri) {
var data = dataUri.slice(dataUri.indexOf(','));
return Buffer.from(data, 'base64');
}