Change cursor for full screen NSWindow - objective-c

Question

I am trying to make an overlay window that will allow drawing at the ShieldingWindowLevel, however when the window appears the cursor is still the default pointer. I would like to change it to the crosshairs. Having controller NSCursors before I am baffled why resetCursorRects is not ever called.
I manually create the window as follows (in my AppController class):
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
// Create the window
NSRect frame = [[NSScreen mainScreen] frame];
// Provide a small area on the right to move the cursor in-and-out of the window.
frame.size.width = frame.size.width - 20;
self.window = [[NSWindow alloc] initWithContentRect:frame
styleMask:NSBorderlessWindowMask
backing:NSBackingStoreBuffered
defer:NO];
[self.window setAcceptsMouseMovedEvents:YES];
[self.window setOpaque:NO];
[self.window setLevel:CGShieldingWindowLevel()];
[self.window setBackgroundColor:[NSColor colorWithDeviceRed:0.0 green:0.0 blue:1.0 alpha:0.2]];
// Create the subview
ScreenOverlayView *subview = [[ScreenOverlayView alloc] initWithFrame:NSZeroRect];
[[self.window contentView] addSubview:subview];
// Add subview and show window
[self.window setContentView:subview];
[self.window makeFirstResponder:subview];
[self.window orderFrontRegardless];
}
With the following NSView subclass:
#implementation ScreenOverlayView
- (void) resetCursorRects {
[super resetCursorRects];
[self addCursorRect: [self bounds]
cursor: [NSCursor crosshairCursor]];
}
// ...
#end
I created a sample project to show this case and posted it to github, the most interesting files are ScreenOverlayView.m and AppDelegate.m.
I should point out that I have also spent a good deal of time trying to get this working with an NSTrackingArea, as you can see in the sample project. Tracking Area works if the mouse enters the view after it has appeared, but not if it is inside to start with. Using MouseEnter and MouseLeave would be fine if I had some way to set the initial cursor, but it will only change for a split second before changing back.
How can I get resetCursorRects to be invoked -OR- how can I set the cursor when I move it to the superview?

Answer 1

The key is that you really need to create a custom subclass of NSWindow, in order to counteract some of the default behavior that borderless windows (NSBorderlessWindowMask) have.
An updated version of your sample project is at http://www.markdouma.com/developer/full-screen-overlay.zip.
In it, I created a custom MDScreenOverlayWindow class that overrides NSWindow's canBecomeKeyWindow method like below:
// Windows created with NSBorderlessWindowMask normally can't be key,
but we want ours to be
- (BOOL)canBecomeKeyWindow {
return YES;
}
This will allow your view to become key and basically all your other stuff to work properly.
The other thing that may be of note is the drawRect: method. (It looks like you may be coming from iOS). You might want to look into NSBezierPath, as it could potentially simplify some of your drawing code. For example, I believe the drawing code you had could be consolidated into the following:
- (void)drawRect:(NSRect)rect {
// the color should probably be "pre-multiplied" by the alpha
// premultiplied version:
[[NSColor colorWithCalibratedRed:0.8 green:0.0 blue:0.0 alpha:0.8] set];
[NSBezierPath setDefaultLineWidth:2.0];
[NSBezierPath strokeLineFromPoint:currentLocation toPoint:downLocation];
}