Put a transparent NSWindow permanently on top of another NSWindow - objective-c

Question

I want to have some UI controls on top of a NSWebView and because of this problem " https://stackoverflow.com/questions/9120868/video-in-nswebview-hides-views-on-top-of-the-nswebview " I now want to add a "transparent" NSWindow, so without the close buttons etc., on top of my NSWebView, hence, on top of my current NSWindow.
How can I achieve this and make sure that this "overlay window" stays in place, even if I move the underlying window?
EDIT:: While #dzolanta's approach works fine, I wonder if it is possible to do it by using an NSWindowController which would allow me to properly use Outlets etc.

Answer 1

Child window is what you need.
Create NSWindow with NSBorderlessWindowMask and define it to be transparent using - setOpaque: and - setBackgroundColor: methods. Then add newly created window as a child of window containing an instance of NSWebView (using NSWindow's - addChildWindow:ordered: method). Moving parent window will automatically cause child window to move.
Update with working code:
CGRect wRect = self.window.frame;
NSView *contentView =self.window.contentView;
CGRect cRect = contentView.frame;
CGRect rect = CGRectMake(wRect.origin.x, wRect.origin.y, cRect.size.width, cRect.size.height);
NSWindow *overlayWindow = [[NSWindow alloc]initWithContentRect:rect
styleMask:NSBorderlessWindowMask
backing:NSBackingStoreBuffered
defer:NO];
overlayWindow.backgroundColor = [NSColor redColor];
[overlayWindow setOpaque:NO];
overlayWindow.alphaValue = 0.5f;
[self.window addChildWindow:overlayWindow ordered:NSWindowAbove];

Answer 2

Swift 3 version using window controller:
final class OverlayWindowController: NSWindowController {
init(frame: NSRect) {
let window = NSWindow(contentRect: frame, styleMask: .borderless, backing: .buffered, defer: false)
super.init(window: window)
window.contentViewController = MyViewController()
window.backgroundColor = NSColor.clear
window.isOpaque = false
}
#available(*, unavailable)
required init?(coder: NSCoder) {
fatalError("init(coder:) is unavailable")
}
}