function erasePixelFast(x, y, pixel) {
  const data = this.data;
  const rdata = this.reverse;
  const dx = x - this.layer.x;
  const dy = y - this.layer.y;
  const xx = dx - this.bounds.x;
  const yy = dy - this.bounds.y;
  const idx = 4 * (yy * this.bounds.w + xx);
  // save old pixel into reverse matrix if not set yet
  if (rdata[idx + 3] <= 0) {
    rdata[idx + 0] = pixel[0];
    rdata[idx + 1] = pixel[1];
    rdata[idx + 2] = pixel[2];
    rdata[idx + 3] = rgbAlphaToAlphaByte(pixel[3]);
  }
  // reset pixel data
  data[idx + 0] = 255;
  data[idx + 1] = 255;
  data[idx + 2] = 255;
  data[idx + 3] = 255;
}
@param {Number} x
@param {Number} y
@param {Array} pixel - Earlier pixel