Collision Geometry

Contrary to what you may think, there are typically two sets of geometry in every game. There is the art, which you of course created and perfected and are very proud of, but we can’t forget the invisible and underestimated collision geometry. As the player moves through your scene, how does the engine know what is a wall? What is a floor? What is a window? When the character is walking down a hallway, what happens when it bumps into a wall? It’s stopped, right? Well, that’s not the actual art the character is running into; it’s collision geometry.

Collision geometry is a simplified, nontextured, and invisible version of the art that determines where the player can walk and what types of surfaces the player is encountering. The art geometry and the collision geometry are normally separated because collision geometry does not need to be as detailed as the art. Now, even though collision is invisible, it still works against your poly count. In fact, if your collision geometry was identical to your art, not only would the poly count be doubled, but the player would always be bouncing off objects or getting stuck or hung up due to the excessive detail. The gameplay would be erratic and rough. Collision is typically very simple, flat, and basic. It doesn’t need small details like textures....