Question

I’m creating an application to capture a small area of the screen and compare it to a library of images saved to disk. I wrote a similar application a few years ago in .net and used bitblt and the WINAPI. Performance is really important and I don’t mind delving into openGL if it would make a difference with performance.

Answer 1

You could use some code like this:

-(NSImage*)captureImageFromRect:(NSRect)captureRect
{
    NSImage *resultingImage = nil;
    CGImageRef image;
    CGWindowID  windowID = (CGWindowID)[[self window] windowNum];
    image = CGWindowListCreateImage(NSRectToCGRect(captureRect), kCGWindowListOptionIncludingWindow|kCGWindowListOptionOnScreenBelowWindow, windowID, kCGWindowImageDefault);
    resultingImage = [[NSImage alloc] initWithCGImage:image size:NSZeroSize];
    CGImageRelease(image);
    return [resultingImage autorelease];
}