I guess you could shift the coordinate axes of the upper left coordinate point to be (0,0) and adjust all other points accordingly.Ok.. maybe I should have put my question a bit better, with a bit more info on what I need this for.
What I have is an object, inside a screen, that is inside another screen. The object can move, and the screen inside the screen is partially-fixed onto the object. If I move the mouse to the left, the screen will follow it to the left, up until the object is on the very right side of the screen which stops it from moving further.
The objects coordinates are based on the large screens origin, and my mouse coordinates are based on the smaller screens plane, which starts in the top left 0,0.
What I am trying to do is to get the mouses coordinates relative to the larger screen.