Cocoa app Create transparent view on top of all mac running applications

Question

I am working on a mac osx application using Xcode. I would like to add a transparent full-screen view/window on top of all applications. So that I could 'draw' on the transparent view, and behind it will be whatever application, safari, word...etc.

I tried like the following

 NSRect rect = [[NSScreen mainScreen] frame];   //this is full screen size, but still with the status bar like time, battery, etc.

 NSWindow *overlayWindow = [[NSWindow alloc]initWithContentRect:rect
 styleMask:NSBorderlessWindowMask
 backing:NSBackingStoreBuffered
 defer:NO];
 overlayWindow.backgroundColor = [NSColor redColor];
 [self.window addChildWindow:overlayWindow ordered:NSWindowAbove];

It's a new full-screen child window of my mac-application. But it's not on top of all applications i am running on my mac.

So my question, How to add the view on top of my mac screen view(not only the top view of my application). Thanks so much!!!

Answer 1

See Apple's FunkyOverlayWindow sample code. In addition to setting the window's level, you will need to set its background color to clear and set it to non-opaque. If it's transparent but you still want it to receive mouse events for drawing (rather than letting them pass through to the windows behind it), you'll need to do [window setIgnoresMouseEvents:NO].

Answer 2

This looks like what you want.

NSWindow has - (void)setLevel:(NSInteger)windowLevel

With this useful predefined levels. Pick one you like. Add or subtract 1 if you want it just above or just below one of these levels.

#define NSNormalWindowLevel          kCGNormalWindowLevel
#define NSFloatingWindowLevel        kCGFloatingWindowLevel
#define NSSubmenuWindowLevel         kCGTornOffMenuWindowLevel
#define NSTornOffMenuWindowLevel     kCGTornOffMenuWindowLevel
#define NSMainMenuWindowLevel        kCGMainMenuWindowLevel
#define NSStatusWindowLevel          kCGStatusWindowLevel
#define NSModalPanelWindowLevel      kCGModalPanelWindowLevel
#define NSPopUpMenuWindowLevel       kCGPopUpMenuWindowLevel
#define NSScreenSaverWindowLevel     kCGScreenSaverWindowLevel
#define NSDockWindowLevel            kCGDockWindowLevel