message: add gl.finsh before fence
diff: @@ -57,6 +57,7 @@ const tmpPixel = new Uint8Array(1 * 4);
  function fence(gl: WebGL2RenderingContext) {
  return new Promise(resolve => {
  + gl.finish()
  const sync = gl.fenceSync(gl.SYNC_GPU_COMMANDS_COMPLETE, 0)
  if (!sync) {
  console.warn('could not create a WebGL2 sync object')
  