But what should I do with the panel that goes in the center?, I mean that's not part of the background, isn't there a way to just use a window for a 3d object? so I still can be able to fade in every element one by one. The solution given by you is a good one but it should not work for me because the panel of the center I'm going to use in the last version will have some details, so I want it to fade in as a separated element, I can do this with a 2D easily but with a 3D I can't