@loaders.gl/gltf/src/lib/extensions/EXT_meshopt_compression.ts

Framework-independent loader for the glTF format

/* eslint-disable camelcase */
import type {GLTF, GLTFBufferView, GLTF_EXT_meshopt_compression} from '../types/gltf-json-schema';
import type {GLTFLoaderOptions} from '../../gltf-loader';
import {GLTFScenegraph} from '../api/gltf-scenegraph';
import {meshoptDecodeGltfBuffer} from '../../meshopt/meshopt-decoder';

// @ts-ignore
// eslint-disable-next-line
const DEFAULT_MESHOPT_OPTIONS = {
  byteOffset: 0,
  filter: 'NONE'
};

/** Extension name */
const EXT_MESHOPT_COMPRESSION = 'EXT_meshopt_compression';

export const name = EXT_MESHOPT_COMPRESSION;

export async function decode(gltfData: {json: GLTF}, options: GLTFLoaderOptions) {
  const scenegraph = new GLTFScenegraph(gltfData);

  if (!options?.gltf?.decompressMeshes || !options.gltf?.loadBuffers) {
    return;
  }

  const promises: Promise<any>[] = [];
  for (const bufferViewIndex of gltfData.json.bufferViews || []) {
    promises.push(decodeMeshoptBufferView(scenegraph, bufferViewIndex));
  }

  // Decompress meshes in parallel
  await Promise.all(promises);

  // We have now decompressed all primitives, so remove the top-level extension
  scenegraph.removeExtension(EXT_MESHOPT_COMPRESSION);
}

/** Decode one meshopt buffer view */
async function decodeMeshoptBufferView(
  scenegraph: GLTFScenegraph,
  bufferView: GLTFBufferView
): Promise<void> {
  const meshoptExtension = scenegraph.getObjectExtension<GLTF_EXT_meshopt_compression>(
    bufferView,
    EXT_MESHOPT_COMPRESSION
  );
  if (meshoptExtension) {
    const {
      byteOffset = 0,
      byteLength = 0,
      byteStride,
      count,
      mode,
      filter = 'NONE',
      buffer: bufferIndex
    } = meshoptExtension;
    const buffer = scenegraph.gltf.buffers[bufferIndex];

    const source = new Uint8Array(buffer.arrayBuffer, buffer.byteOffset + byteOffset, byteLength);
    const result = new Uint8Array(
      scenegraph.gltf.buffers[bufferView.buffer].arrayBuffer,
      bufferView.byteOffset,
      bufferView.byteLength
    );
    await meshoptDecodeGltfBuffer(result, count, byteStride, source, mode, filter);
    scenegraph.removeObjectExtension(bufferView, EXT_MESHOPT_COMPRESSION);
  }
}