There are many reasons for designing one button games.

-         Many cell phones don’t support two simultaneous key presses.

-         Most users like to play with their thumb, so one button games are the most appropiate.

-         And let’s remember that difficult interfaces are the worst enemies of “suspension of disbelief”, in other words, a hard or confuse interface it’s a sure way to terminate the user’s immersion in your game.

When you’re designing a game, you can turn this limitation into an advantage. If you manage to design a game that requires the user to take care of only one button, your game will be simpler. And simpler is always good. Just think about explaining how to play, the manual or the Help section… It can’t be easier.

Let’s analyze this interface.

A button has only two states: pressed and released.

1- A simple interface will rely on only one button state. For example, imagine a first person game where objects move in front of you, and you have to shoot the bad guys when they are exactly in the center of the screen. Your only duty is to shoot at the right time. Here Gameplay is all about timing. It may get boring with time. That’s why we add more elements to basic Gameplay, but this time we’ll do it without adding more elements to the interface.

2- Let’s use the two states. Each state can be directly related to the state of your character. For instance, think of game where you control a gate. If good things came across, you open the gate releasing the button. Otherwise you keep it close pressing the button. As before, here Gameplay is about timing, but now there are two states to care about. 

3- I believe we can really take advantage of this kind of interfaces when we add a default behavior to our characters. Pressing or releasing the button will alter or keep this behavior.

For instance, imagine a version of the popular Snake game, where the snake always runs forward and right, in circles. When you press the button, the snake runs forward and left. So, by pressing and releasing the button with the right rhythm you can move forward the snake running in half circles, in a rather “snaky” way.

4- Let’s go a bit further. Why don’t we change the default behavior over time?

Let’s think of a classic platform game that scrolls to the right. In this game, when an enemy approaches, pressing the button means firing you gun. If the enemy is too near, it means kicking. And if close to a wall, pressing the button will make your character jump. In a ladder it will climb until released … and so on. All with only one button.

Finally, I’d like to share with you my experience with our last game. It’s called “Poncho Balón” and it’s about a street soccer ball that dreams of being at the world cup. You have to steer him through obstacles and jumping over evil guards. This game is intended for the Latin American market where MIDP 1 devices are still very present, so the restriction about having only one simultaneous key press is very important.

The most complicated issue about this limitation is how to handle diagonal jumps.

We solved this problem by giving the ball a never ending bouncing.

At the beginning of the level you care about thrusting the bounce. When the ball is going up, pressing UP will thrust the ball up and the bounce will be bigger. After having a reasonable bounce you have to care about moving to the right. You do that by pressing the RIGHT key at the right time to jump over guards and obstacles.

Well, as you can see, I really like this kind of interfaces.

If you're also interested in this subject, I recommend you these articles:

- One Button Games, by Berbank Green (June 2, 2005)

Please have a look at the 8 examples in the middle of the article.

-  GDC: Success Factors of One-Button Casual Mobile Games, by Brandon Sheffield (March 22, 2006)