code: function rectshift(a, b) {
  	if(a.x > b.x + b.width ||
  		a.x + a.width < b.x ||
  		a.y > b.y + b.height ||
  		a.y + a.height < b.y) {
  		return 0;
  	} else {
  		var overlap = b.x + b.width - a.x;
  		return overlap;
  	}
  }
docs: see if two rectangles overlap. if so, return the distance that A needs to shift to the right to avoid overlapping.