I'm looking for a method to define an area of the screen that the mouse cannot leave. I have been directed by rob mayoff, the answerer of this question, that I can use a Quartz Event Tap to detect mouse events. This puts me part of the way to the solution to THIS question.

I need to define an irregular area of the screen, not just a rectangle, that the mouse cannot leave. I have been researching this and the only idea I can come up with is using a bitmap to define the irregular area, as it will be very oddly shaped. However, I am open to solutions other than using a bitmap.

Since this must be done on a Mac, I've determined that I will have to use objective C / Cocoa .

I need to know how to define the area and, equally importantly, how to find the closest point in the area to the mouse (so that I can move the mouse to it if the mouse tries to move outside of the area).

This is similar to what the restricted area will look like:

[edit:]

Okay, I've come up with part of the answer to this. If I can do a basic (light-weight) point collision detection on the image mask, I can use a simple algorithm to detect the closest point to the mouse on the black area of the image.

I could do this by calculating distance between a pre-defined point (P) inside the black area of the image and the target mouse position (T), taking the midpoint (M), then checking if the midpoint is inside or outside of the shape (black or white, respectively). If M is inside the shape, then move the P to M, otherwise move T to the M, continuously recalculate this until the distance between T and P is 1 pixel or less, then move the mouse to the final calculated position.

All of that being said, I still need some way to test the position of the mouse against that same position on the bitmap (assume the bitmap is the same resolution as the monitor), and check if that point is black or white. All of this needs to be done in the background, without this application actually having focus, or the bitmap being visible... is this possible?