I'm currently working on a survival shooting game roughly similar to gunbros or minigore, with enemy constanly generated and moving toward the player, inside a closed area larger than the window... (vertical and horizontal scrolling)
What I'd like to do is an arrow for each enemy off-screen, like an indicator of the incoming danger... Something like that (you see the blue arrows?):
My problem is that my enemies are on a layer with paralax while the arrows are on the GUI layer without parallax. They're not in the same "system of coordinates" and I don't know how to create a link between them.
I'd like to know if there is a way to know the coordinates of an element from a layer but on another layer... a kind of conversion or something, giving the coordinate of an object in a specific layer). That would be awesome since I'd like to use this system not only for the enemies but also for bonuses and other things... A crucial element of the game, really.
Thanks in advance for your help!