WASD and spacebar
Purpose: To place 3d objects in a 2d picture and let them interact with the environment.
Effect: Computer generated 3d object interacts with 2d picture.
How it works: Though many people see it as a problem, I have used the depth-sorting issue to my advantage. I set the background to my 2d picture. I created a model of the 3d scene(by hand). I then made it into a window of sorts, so that objects in front of it would be visible, and objects behind it would be invisible.