Start the app in the center of the screen

[ZolAnder85]

Is your feature request related to a problem? Please describe.
The window always opens in the lower left corner of the screen.

Describe the solution you'd like
Opening the app should place its window in the center of the screen, or (as many built-in apple apps do) a little higher than the center.

Describe alternatives you've considered
It might also be good to save the window position. De default position should still be improved though.

[ZolAnder85]

Few years ago I have written a "nibless" cocoa app for an OpenGL based multiplatform game engine.
This is how I set up the window:

init(app: NSApplication) {
	let screen = NSScreen.main()!
	let rect = NSMakeRect(
		screen.visibleFrame.origin.x + screen.visibleFrame.width / 2 - CGFloat(preferredWidth) / screen.backingScaleFactor / 2,
		screen.visibleFrame.origin.y + screen.visibleFrame.height / 2 - CGFloat(preferredHeight) / screen.backingScaleFactor / 2,
		CGFloat(preferredWidth) / screen.backingScaleFactor,
		CGFloat(preferredHeight) / screen.backingScaleFactor
	)
	window = NSWindow(
		contentRect: rect,
		styleMask: [ NSTitledWindowMask, NSClosableWindowMask, NSResizableWindowMask ],
		backing: .buffered,
		defer: false
	)
	window.title = Bundle.main.infoDictionary!["CFBundleName"] as! String
	view = OpenGLView(frame: rect)
}

Not sure if this speeds things up for you, or where you would put this in your code. Maybe some params in the storyboard does the trick. Also, you do not need the screen.backingScaleFactor, which I used because preferred size of the game is in physical pixels.