ludic/docs/language/app/app-window_hide.md

id	name	category	kind	tokens	sig	tip	order	ns	member
app-window_hide	App.window_hide	app	namespace-method	App.window_hide	App.window_hide() -> void	Take the game's window off the screen.	3	App	window_hide

Takes the game's window off the screen without closing it: its GL context or Vulkan surface, its size and its contents are kept, and the program goes on running — a hidden window does not end the run. App.window_show brings it back. It is how a launcher steps aside while the game it started with Process.spawn runs.

Keep the frame loop going while hidden so the child can be polled, but there is nothing to see: skip the drawing, and throttle the loop yourself — a hidden window is not paced by the display, so an unthrottled loop spins. It does not touch the boot splash (App.splash_hide does). Safe to call when there is no window yet, and twice. Headless there is no window and the call lowers to nothing.

program Launcher {
  state Child { game: int = -1 }
  function play(c: mut Child) -> void {
    c.game = Process.spawn(game_path(), new []string)
    if c.game >= 0 { App.window_hide() }
  }
  handler Watch(c: mut Child) phase Update {
    if c.game >= 0 and Process.poll(c.game) != -1 {
      Process.free(c.game)
      c.game = -1
      App.window_show()
    }
  }
}

orderOut: on macOS; ShowWindow(SW_HIDE) on Windows, which also forgets any key held as the window went.