function drawAt(x, y, size, color) {
  const xpad = Math.floor(size / 2);
  const ypad = Math.floor(size / 2);
  this.fillRect(
    x - xpad, y - ypad,
    size + xpad, size + ypad,
    color
  );
}
@param {Number} x
@param {Number} y
@param {Number} size
@param {Array} color