message: Improving isPixelColored performance
  We don't need to allocate more than 4 ints to read our
  target pixel.
diff: * colored, and false else.
  */
  export function isPixelColored(gl: WebGLRenderingContext, x: number, y: number): boolean {
  - const pixels = new Uint8Array(gl.drawingBufferWidth * gl.drawingBufferHeight * 4);
  + const pixels = new Uint8Array(4);
  gl.readPixels(x, gl.drawingBufferHeight - y, 1, 1, gl.RGBA, gl.UNSIGNED_BYTE, pixels);
  return pixels[3] > 0;
  }
  