Question

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:

Answer 1

Load your mask into an NSBitmapImageRep. For example:

    mask = [NSBitmapImageRep imageRepWithData:[NSData dataWithContentsOfFile:[[NSBundle mainBundle] pathForImageResource:@"mask"]]];

Test your position against the mask like this:

- (BOOL)isAllowablePoint:(CGPoint)point
{
    if (point.x < 0 || point.y < 0 || point.x >= mask.pixelsWide || point.y >= mask.pixelsHigh)
        return NO;
    NSUInteger pixel[4];
    [mask getPixel:pixel atX:point.x y:point.y];
    return pixel[0] == 0;
}

Make sure your mask image is saved at 72 dpi. You can check/fix this by opening the image in Preview. Choose Tools > Adjust Size, and make sure the resolution box says 72.