Function subtractOffset

Subtracts A-B. Applies to x, y, width & height

subtractOffset(
 { x:100, y:100, width:100, height:100 }, 
 { x:10, y:20,   width: 30, height: 40 }
);
// Yields: {x: 90, y: 80, width: 70, height: 60 }
Copy

If either a or b are missing x & y, 0 is used.