Web based School

Chapter 8

User Input in Games


Just in case you had a hard weekend, you begin this week with a pretty easy lesson. ToChapter you learn about user input in games, including the input devices supported by Java and how they are used in gaming scenarios. You'll be spared the details of how to actually communicate with input devices in Java until tomorrow's lesson. Nevertheless, toChapter's lesson covers some important issues in regard to game design from a user input perspective.

ToChapter's lesson serves as a good primer for tomorrow, when you learn about the specific Java programming techniques necessary for handling user input in games. For toChapter, though, just relax and enjoy a break from the source code!

The following topics are covered in toChapter's lesson:

  • Gaming and user input
  • User input devices

Gaming and User Input

User input is the means by which the user interacts with a game.

Considering the fact that user input encompasses the entire communications between a player and a game, you would think that designing an intuitive, efficient interface for user input would be at the top of the list of key game design elements. However, that isn't always the case. With all the hype these Chapters surrounding real-time texture-mapped 3D graphics engines and positional 3D audio in games, effective user input support is often overlooked. In fact, user input is perhaps the most overlooked aspect of game design, which is truly a tragedy. It's a tragedy because user input support in a game directly impacts the playability of the game; and when the user input isn't effective, the play suffers.

You see, I'm from the old school of game players, and I still remember paying homage to the gods of gaming with my hard earned allowance in arcades, well before there was an option of playing anything other than Pong at home. In return for my quarter offerings, the game gods usually provided me with incredibly fun games that usually had to survive on their playability alone. Because the hardware at that time simply couldn't provide a very high level of graphic and sound intensity, the game developers were forced to make up for it with game play. Of course, they didn't consider their focus on playability as making up for anything; with the limited graphics and sound capabilities at the time, they didn't have an option.

Let me give you a quick example of what I'm talking about in regard to playability and user input. One of my all-time favorite games is Ring King, which is a boxing game for the Nintendo Entertainment System (NES). Ring King is definitely considered "old" by current gaming standards-possibly even ancient. Compared to current games, it has weak graphics, animation, and sound. However, I still play the game simply because it plays so well. And that playability is largely based on how the game handles user input; it allows for very subtle timing when you punch and dodge, which goes a long way in a boxing game! Since then, I've tried to find a modern replacement for Ring King, but I've had no luck. When I get beyond the fancy graphics and sound, I start missing the responsiveness of the controls in my old favorite. I'm still looking, though.

Lest you think I'm being overly critical of current games, plenty of recent games have incredible user input support, along with awesome graphics and sound. However, an equal number of recent games have killer graphics and sound, but little substance when it comes to playability and user input. These types of games might be visually stunning and fun to listen to, but they rarely have any lasting appeal beyond the initial "Wow!"

Now, let me step down from the soap box and get to the real point, which is that you should carefully plan the user input for your games just like you carefully plan the graphics, sound, and game logic. This doesn't mean only deciding between supporting a keyboard or a mouse for the user interface. It means putting some real thought into making the user interface as intuitive as possible. You want the controls for the game to feel as natural as possible to the player.

User Input Devices

Input devices are the physical hardware, such as mice and keyboards, that allow a user to interact with a game.

Input devices all perform the same function: converting information provided by the user into a form understandable by the computer. Input devices form the link between the user and your game. Even though you can't directly control the input device hardware, you can certainly control how it is interpreted in your game.

Although some really neat input devices are available for pcs and Macintoshes, such as flightsticks and digital joysticks, you're working with Java, so you have to think in terms of supporting multiple platforms and therefore a fairly limited amount of input devices. As a matter of fact, the current set of input devices supported by Java consists of two devices-the keyboard and the mouse.

Trackballs have also grown in popularity as input devices recently. Trackballs are functionally very similar to mice and are often treated just like mice from a software perspective. Fortunately, Java doesn't discern between trackballs and mice, so the mouse support in Java indirectly supports trackballs as well.

It might sound limiting to not be able to support joysticks in Java, but it is simply a fact of life that joysticks aren't considered a "standard" input device by the computer community at large. Arguably, it would be nice to be able to support joysticks as an optional input device, but you'll simply have to hope for the support in a future release of Java. Even without joystick support, however, creative user input strategies can still be implemented. Personally, I like using either the keyboard or mouse for most games, rather than a joystick. But I'm kind of strange in that respect!

Sun has announced plans for extensions to the Java language that will include broader multimedia support. It's not clear whether joysticks and other game-oriented input devices will be supported in these extensions, but there is no reason that they couldn't be supported. We'll just have to wait and see.

The Keyboard

The keyboard has been the computer input device of choice since its inception. Although mice, joysticks, flightsticks, and many other user input devices have brought extended input capabilities for the game player, none is as established as the keyboard. At the bare minimum, you can always count on a game player having a keyboard.


The keyboard is a surprisingly useful input device for a wide range of games. The sheer amount of keys alone gives the keyboard appeal for games that require a wide variety of user input. Even more useful in the keyboard is the natural feel of pressing keys for games requiring quick firing and movement. This usefulness is evident in the amount of arcade games that still use buttons, even when powerful digital joysticks are readily available. Keys (or buttons) simply are easier to use in many games, including those with many input combinations.

When assessing the potential use of the keyboard in a game, try to think in terms of the most intuitive user interface possible. For example, any game involving the player moving an object around would benefit from using the arrow keys. A good example is DOOM, which makes creative use of a keyboard-specific feature that greatly enhances the playability of the game. The left and right arrow keys, when used alone, rotate the player left and right in the game world. However, when the Shift key is held down, the same left and right arrow keys cause the player to strafe, meaning that the player moves sideways without changing direction. This seemingly small enhancement to the keyboard controls goes a long way when playing the game.

When you're deciding on specific keys to use for keyboard controls in your game, consider the potential limitations on players using other platforms or hardware configurations. For example, I primarily use a Windows 95 pc equipped with a Microsoft Natural keyboard. If you aren't familiar with these keyboards, they are split down the middle for ergonomic reasons. If you don't use one of these keyboards, it might not occur to you that key combinations near the center of the keyboard will be separated a few inches for people like me. So, remember that if you use the G and H keys (or other middle keys) in your game, and it plays well for you, it might not work out so well for players with different keyboards.

This might sound kind of picky, but part of Java programming is trying to make everyone happy. Remember that Java games can be enjoyed by a wide range of computer users. You should make it a goal to do everything in your power to appease all of them. Think of it this way: How many times in the past have you had the opportunity to write one set of source code and have it work on such a wide range of computer systems? I have personally been involved with cross-platform multimedia development using C++, and it's not very fun. My advice is to embrace Java and its support for multiple platforms, and be open-minded when it comes to making decisions that affect users of other platforms!

Now, where were we? Keyboards! The most common keys used on the keyboard in games are the arrow keys. If you're writing an action game, you might also have keys for firing and selecting between weapons. When you're deciding on the keys to use, keep in mind things like the creative usage of the Shift key in DOOM. If you can limit the number of primary game control keys by making use of a secondary key such as Shift, you've made the game controls that much easier to use.

Rapid Fire

A common feature in action games is rapid fire, which involves firing multiple times while a key is being held down. I don't want to burden toChapter's lesson with any source code, but I would like to briefly cover how rapid fire could be implemented in Java using standard keyboard support. As you will learn tomorrow, key presses in Java are handled as events. For now, don't worry too much about what an event is, except that it is something you can write code to respond to. The importance is that an event occurs for each key press, which means that you have the opportunity to respond to each key press (and key release).

You don't, however, have the opportunity to respond to keys being held down, which means that there is no direct way to implement rapid fire. Alas, there is a fairly painless work-around! The solution is to set a boolean member variable when a key is pressed, and then fire the bullets in an event loop based on this boolean variable being true. You receive a key release event when the user lets go of the key, in which case you simply set the boolean variable back to false. You control the speed of the rapid fire by altering the speed of the event loop or by using a separate delay counter.

The Mouse

Although the keyboard is firmly in place as the most necessary of user input devices, the graphical nature of the Web establishes the mouse, or a similar pointing device, as a standard input device as well. The mouse, however, doesn't share the wide range of input applications to games that the keyboard has. This stems from its primary usage as a point-and-click device; if you haven't noticed, lots of games don't follow the point-and-click paradigm.


In regard to gaming, the usefulness of the mouse is dependent totally on the type of game and, therefore, the type of user interaction dictated by the game. However, as quickly as some people write off the mouse as being a useless interface in some games, others praise the fine control it provides. A good example is DOOM. Personally, I think the keyboard is much more responsive than the mouse and the keyboard enables me to get around faster and with more control. But I have friends who feel lost playing the game without a mouse.

Clearly, this is a situation in which the game designers saw a way to provide support for both the keyboard and mouse. With the exception of the most extreme cases, this should be your goal as well. Different game players like different things, and the safest solution is to hedge your bets and support all input devices whenever possible. By following this simple rule, you can develop games that can be appreciated and enjoyed by a broader group of game players.

Interpreting Movement

Similar to the keyboard, Java support for the mouse is event-driven. You'll learn more about the details of mouse events tomorrow, but right now I want to cover the different interpretations of mouse movement. The standard Java mouse event handlers provide you with the current position of the mouse whenever the mouse is moved. This position is referred to as the absolute position of the mouse.

Absolute position is the specific on-screen location of the mouse.

Figure 8.1 shows an example of absolute mouse position.

Figure 8.1 : Absolute mouse position.

The other type of position that is important when examining mouse movement is the relative position of the mouse.

Relative position is the position of the mouse relative to its prior position.

Relative mouse position is more useful in games because you are usually concerned with whether the user moved the mouse left or right, instead of whether the mouse is at position (34, 272), for example. Figure 8.2 shows an example of relative mouse position.

Figure 8.2 : Relative mouse position.

Even though Java provides no direct support for relative mouse movement, you can easily calculate a relative position by saving the prior position and comparing the two. In this scenario, you would maintain the prior mouse position in a member variable, such as a Point object. The mouse movement event handler calculates the relative mouse position as the differences between the X and Y values of the current mouse position and the prior mouse position stored in the member variable. These differences can then be used to determine how an object in a game is moved. For example, a positive X difference in relative position would correspond to an object being moved to the right.

Relative positioning is useful in a wide variety of games-basically, any game in which you control something by specifying a change in movement rather than an absolute location to move to. A good example is a flight simulator, in which you control small changes in the direction and altitude of the plane, rather than modifying its exact position in the sky. An example of a game that would work better with absolute mouse positioning is a Hogan's Alley type game, in which the mouse's movement maps directly to the movement of a gun sight used to shoot bad guys.


ToChapter you learned about user input in games, including some useful tips and problems to watch out for when designing the user input support in your own games. You also learned about the two user input devices supported by Java, the keyboard and mouse, along with some suggestions about how to use them. You learned how rapid fire can be implemented using Java keyboard support, and you finished up with the two fundamental types of mouse positioning and how they are used in games.

Although somewhat brief, toChapter's lesson covered some important issues when it comes to making determinations about user input in games. The goal of toChapter's lesson is mainly to encourage you to put some thought into how you design the user input support in your games. Tomorrow you get to put these design ideas to work by learning exactly how to handle user input in Java.


QWill Java ever support more input devices, such as joysticks?
AIt's hard to say for sure, but Sun has promised more extensive multimedia support in a future release of Java. Because joysticks are generally considered multimedia input devices, support for them might very well appear in a future release.
QAre there any games that wouldn't require keyboard support?
ASure. Any game that requires extensive point-and-click style input, such as a card game, would probably be fine without any keyboard support. However, if you can figure out a way to add keyboard controls, by all means go for it.
QIs it possible to mix keyboard and mouse controls?
AOf course! This actually hits on an interesting point not covered in toChapter's lesson: Many games work great by combining mouse and keyboard controls. A good example is the strafing feature in DOOM, which also works with the mouse; it is activated by holding down the Shift key while moving the mouse left or right.


The Workshop section provides questions and exercises to help you get a better feel for the material you learned toChapter. Try to answer the questions and at least think about the exercises before moving on to tomorrow's lesson. You'll find the answers to the questions in appendix A, "Quiz Answers."


  1. What are the two types of mouse movement?
  2. If you had to choose between supporting the keyboard or the mouse, which would you choose?
  3. How is interrupt 16h used to handle key presses?


  1. Play some commercial games and pay attention to what input devices are supported and how.
  2. Find out the limitations of input devices on computer systems other than the type you have. For example, are some keys in different locations or missing altogether?
  3. Clean the roller mechanism inside your mouse; you need the mouse in tip-top shape for the rest of this week's lessons!