I'm trying to create a simple drawing program that creates a square where the user clicks and drags.

The square displays correctly as long as either x or y remain positive with respect to the original click position.

If both x and y are negative with respect to the original click position, the square grows/shrinks, but also wanders about the screen.

Is there a way to swap the origin point from top-left to bottom-right or to keep the square from wandering?