How to have a button which is projected outside the NSView?

I want to implement a button which is projected outside the NSView. The similar button is shown in below image.

If you have to have a view overflowing the window, you can't do that using the masksToBound property of CALayer. You need to use a child borderless window and position it correctly.

Here's an example (in ObjC):

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
    // Insert code here to initialize your application


    NSRect windowFrame = self.window.frame;
    NSRect childWindowFrame = {
        .origin.x = CGRectGetMidX(windowFrame) - 25,
        .origin.y = CGRectGetMinY(windowFrame) - 25,
        .size.width = 50,
        .size.height = 50,
    };

    NSWindow *childWindow = [[NSWindow alloc] initWithContentRect:childWindowFrame
                                                        styleMask:NSWindowStyleMaskBorderless
                                                          backing:NSBackingStoreBuffered
                                                            defer:YES];
    childWindow.backgroundColor = [NSColor clearColor];
    childWindow.contentView.wantsLayer = YES;
    childWindow.contentView.layer.backgroundColor = [NSColor redColor].CGColor;
    childWindow.contentView.layer.cornerRadius = 25.0;



    [self.window addChildWindow:childWindow ordered:NSWindowAbove];
}

The red circle in this screenshot is the child window.