I'd like to make an isometric run-jump style platformer. The player should be able to jump on top of platforms above the floor, hit the side of objects etc. I'll be using a 2d game engine so I wouldn't like to emulate full 3d collision for dimensions I'm not using. I'm thinking objects in the game should be placed using: x, y, width, height, and z for depth. Using those values, how should I detect collisions?