ApplicationDelegate.m

@implementation ConcordeAppDelegate

@synthesize window, overlay;

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {    
    // Make the overlay window transparent and borderless
    [overlay setStyleMask:NSBorderlessWindowMask];
    [overlay setBackgroundColor:[NSColor colorWithDeviceRed:0.0 green:0.0 blue:0.0 alpha:0.0]];
    [overlay setOpaque:NO];
    
    // Add the overlay as a child window
    [window addChildWindow:overlay ordered:NSWindowAbove];
    
    // Align it with the CNWorldView and make visible
    NSRect overlayFrame = [window contentRectForFrameRect:[window frame]];
    [overlay setFrame:overlayFrame display:YES];
}

@end