This is the final blog I am doing for my Software Development Practices subject. It is on a game, so you probably will find it less dry than the previous four blogs.

Cellfactor Revolution is a computer game that, in my opinion, has some serious interaction design flaws. For those that don’t know, Cellfactor is a free first person shooter game released by Ageia as a marketing tool to attract people to buy their hardware physics processors. Cellfactor is a heavily physics-based game, which means that you use physics (aka being able to move objects realistically in game) to kill other players. For example, you might use your psychic powers and push a stack of boxes onto another player to kill them. You might fire a dart into an enemy player which causes all objects that are not tied down to be drawn to that player, crushing him. It is intensely physics based and needs an Ageia PhysX card to be played properly, hence why it has been released free to attract people into buying Ageia’s hardware.

From an interaction perspective, Cellfactor uses the standard first person shooter (FPS) controls: WASD for movement and the mouse to look around and fire weapons. But Cellfactor introduces new the new physics abilities that confuse the standard key-bindings that a seasoned FPS player would use. Obviously, in an attempt to make it easier to play, the developers set the default key bindings for the physics push and pull abilities to Ctrl and spacebar. This is where the problems start.

As any regular FPS player probably knows, Ctrl and spacebar are normally bound to crouch and jump. So by changing the default controls, Cellfactor’s developers have either forced you to relearn controls (a difficult and frustrating process: an exaggeration would be to imagine trying to relearn how to type on a Dvorak keyboard), or forced you to change them manually to something else. That doesn’t sound too bad until you figure out that there aren’t another good two keys you can bind physics push and pull to. See, in Cellfactor, you don’t just push and pull. You combine those abilities with other key-presses like Alt and right-click to perform special physics abilities like physics shockwaves. I tried to bind push and pull to mouse 4 (the thumb button on the mouse) and the F key and found it a real hand-bender to try and press mouse 4 + right-click + alt during an in-game fire-fight. Note that if you are able to change yourself to use Ctrl and spacebar as push and pull then you don’t get these finger contortions, which is probably why they are set to be the defaults.

In Cellfactor, you can play as different classes of player: a psychic, a soldier, and a mechanised robot. This introduces another problem: each class has different key bindings. For example, using default controls, pressing F will cause you to hyperjump if you are the robot, but pressing F when you are the soldier causes you to throw a proximity mine. Trying to remember what key does what when you are using a certain class at the same time as trying to bend your fingers unnaturally to press mouse 4 + right-click + F at the same time as using WASD is as difficult as trying to parse and read this sentence.

The solution requires a rethink as to how the player should interact with the physics abilities. What I would do is to bind the separate physics abilities such as push, pull and each of the special physics abilities to a number key. The player could then press the number key of the ability he wants, for example key 3 for physics push, and then use the standard FPS left and right-click to prepare and “fire” it. It is standard behaviour in FPS games to change binding of the number keys to different weapons or abilities in different classes, which reduces the player class / key-binding issue since people are used to it already.

I’m surprised that these problems weren’t encountered during play-testing. Either the developers didn’t do enough testing (a possibility because of the restricted budget this free game probably had), or they decided that relearning the controls was an acceptable thing they were willing to force players to do. It is possible they tried my idea that I discussed above and found that it prevented the player from using the physics abilities as quickly as the currently implemented design (after learning it).

In the end, the interaction design problem behind Cellfactor only affects those too stubborn or those that find it too hard to relearn their controls. It would also affect those who switch between games, since having to mentally switch between Cellfactor controls and Counter-Strike controls all the time would be annoying and frustrating.