Stores a screenshot of a window to disk as PNG

storeWindowImageToFile

@implementation NSWindow (JSTalk)

- (BOOL) storeWindowImageToFile:(NSString*)fileName
{
    CGWindowID windowID = (CGWindowID)[self windowNumber];
    CGWindowImageOption imageOptions = kCGWindowImageDefault;
    CGWindowListOption singleWindowListOptions = kCGWindowListOptionIncludingWindow;
    CGRect imageBounds = CGRectNull;
    
    CGImageRef windowImage = CGWindowListCreateImage(imageBounds, singleWindowListOptions, windowID, imageOptions);

    NSMutableData *data = [NSMutableData data];
    CGImageDestinationRef destination = CGImageDestinationCreateWithData((__bridge CFMutableDataRef)data, kUTTypePNG, 1, NULL);
    if ( destination ) {
        CGImageDestinationAddImage( destination, windowImage, (__bridge CFDictionaryRef)@{
                                                                                 (NSString*)kCGImageDestinationLossyCompressionQuality: [NSNumber numberWithDouble:0.7],
                                                                                 (NSString*)kCGImageDestinationBackgroundColor: (id)[[NSColor clearColor] CGColor]
                                                                                 });
        CGImageDestinationFinalize( destination );
        CFRelease(destination);        
    } else {
        return NO;
    }
    
    fileName = [fileName stringByExpandingTildeInPath];
    return [data writeToFile:fileName atomically:NO];
}

@end