Collision Detection in AAA Games
Have you ever found yourself running into an invisible wall or gotten trapped on a small ledge? That's your video game's Collision Detection acting up. We got some help from someone in the industry to bring some light on the subject.
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---------Brad Hines' blurb on Collision Detection---------
Most AAA titles these days have at least a few issues with collision. As we move forward in quality in games, and with games getting more immersive, collision issues are more and more noticeable to the player. With new gen consoles having more realistic graphics, we're more easily immersed in what we're playing. Anything that reminds us that we're playing a video game will break that immersion, and causes us to have an uncomfortable experience. This is why you see a lot more minimalist UI in newer games - because in theory, more UI means less immersion. Immersion is the key reason why collision issues are so disturbing to a player - if it looks like the character should be able to go somewhere, walk over something, or climb up something, they should. Collision is, however, a complicated system and tends to be different in most game engines, so there are a lot of things that can have an effect on how it interacts with the player character. I'll get into the details below, which will hopefully provide a useful perspective on collision. As a caveat, this is written from a level designer's perspective. There may be programming related details that I'm fuzzy on.
Collision, typically, is how the player character physically interacts with an object or terrain in the world. It can be built in many different ways, but most commonly it is a separate part of a mesh, built specifically to collide with the player. If you have a wall, for example, with a bunch of tiny details such as bricks, piping, windows, and so forth, usually the player collision will be built as a flat plane in front of all the details. This is two-fold: to provide a smooth experience for the player's navigation, and to lessen the burden on the processing of the player's collision. If the engine has to calculate how the player collides with every tiny detail on an object, you'll typically see a pretty drastic effect on the framerate of the game.
You may also have cases such as in third-person games where there is even a separate mesh for camera collision. If you've ever seen the camera suddenly get pushed inside your player character and see their eyeballs and mouth sack, you've likely seen a problem with camera collision. Usually this collision should be closer to the shape of the actual mesh, so that its slightly further away from where the player is colliding with the mesh. This allows the camera to fit between the player and whatever object they're colliding with. This isn't always possible, but it certainly smooths things out when it happens.
Typically, collision is the responsibility of an environment artist or level artist to create. In most cases, a game designer or level designer will also create or modify the collision to better suit the player's experience. If you were to enable the visibility of collision in most linear levels of AAA games, you might see something that looks like a very simple tunnel, whereas the environment appears to be complex. This shows a good example of synergy between art and design - art has provided an immersive environment, while design has provided a smooth experience. This starts to break down when, lets say, you run into an invisible wall in a location where it looks like the player should absolutely be able to go.
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