The easiest method to capture a PNG screenshot of NSWindow

gistfile1.txt

@interface NSWindow (JKScreenShot)
- (NSData *)pngScreenshotData;
@end



@implementation NSWindow (JKScreenshot)

- (NSData *)pngScreenshotData
{
  // This can be kCGWindowImageBoundsIgnoreFraming if you don’t want to include ornamentation like the shadow
  CGWindowImageOption imageOptions = kCGWindowImageDefault;
	
  CGWindowID windowID = (CGWindowID)[self windowNumber];
  CGWindowListOption singleWindowListOptions = kCGWindowListOptionIncludingWindow;
  CGRect imageBounds = CGRectNull;
  CGImageRef windowImage = CGWindowListCreateImage(imageBounds, singleWindowListOptions, windowID, imageOptions);
  NSBitmapImageRep *newRep = [[NSBitmapImageRep alloc] initWithCGImage:windowImage];
  NSData *pngData = [newRep representationUsingType:NSPNGFileType properties:nil];
  CFRelease(windowImage);
  return pngData;
}

@end