Freehand Drawing

function intersection(rectA, rectB) {
  const left = Math.max(rectA.x, rectB.x);
  const top = Math.max(rectA.y, rectB.y);
  const right = Math.min(rectA.x + rectA.width, rectB.x + rectB.width);
  const bottom = Math.min(rectA.y + rectA.height, rectB.y + rectB.height);

  return {
    x: left,
    y: top,
    width: Math.max(0, right - left),
    height: Math.max(0, bottom - top)
  };
}