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and responding to user input. If the function doesn’t return JOYERR_UNPLUGGED, you’re in good shape. When working with joysticks in the Win32 API, you always reference a joystick using a unique ID. This ID must be one of the built-in joystick IDs (JOYSTICKID1, JOYSTICKID2, and so on). In the case of the previous sample code, the JOYSTICKID1 ID checked out okay, so it’s the ID you must use to continue interacting with the same joystick. The joyGetPos() function is the function you call to check the status of the joystick, which is how you determine if the user has interacted with your game via the joystick. The status of the joystick is stored in the JOYINFO structure, which is defined as follows: typedef struct { UINT wXpos; UINT wYpos; UINT wZpos; UINT wButtons; } JOYINFO; You’ll notice that the JOYINFO structure is designed to accommodate joysticks with up to three axes of movement: x, y, and z. The first three members of the structure (wXpos, wYpos, and wZpos) indicate the position of the joystick with respect to each of these axes. The final member, wButtons, indicates the state of the joystick buttons. The wButtons member supports up to four buttons, as indicated by the following constants: JOY_BUTTON1, JOY_BUTTON2, JOY_BUTTON3, and JOY_BUTTON4. Earlier, I mentioned that Windows supports up to six axes and 32 buttons on joysticks, but the JOYINFO structure is obviously more limited than that. The reason for this disparity is because the full range of joystick features are only available through the DirectX game API, which is significantly more complex to use than the built-in Win32 joystick support. If you’re planning on supporting a gyroscopic nuclear-powered virtual reality game helmet in your games that takes advantage of all the axes and buttons possible, you definitely need to get to work learning DirectX. Otherwise, I think you’ll find the Win32 approach to joystick handling to be sufficient. In order to examine a JOYINFO structure to see what’s happened to a joystick, you must first obtain the joystick state using the joyGetPos() function, which is the same function you used to see if a joystick was plugged in. Following is a code example that examines a JOYINFO structure to see if the first joystick button is being pressed: JOYINFO jiInfo; if (joyGetPos(JOYSTICKID1, &jiInfo) == JOYERR_NOERROR) if (jiInfo.wButtons & JOY_BUTTON1) // Button 1 was pressed! This code calls the joyGetPos() function to fill a JOYINFO structure with information about the current joystick state. If the return value of the function is JOYERR_NOERROR, there was no problem retrieving the information and we can continue. The bitwise AND operator (&) is then used with the wButtons member of the JOYINFO structure and the JOY_BUTTON1 constant to see if button 1 on the joystick is being pressed. You can use the same approach to look at other joystick buttons. You’re probably wondering why I’ve avoided talking about the other members of the JOYINFO structure, and how they are used to determine the position of the joystick handle. The reason for this has to do with the fact that you need to understand the range of values possible for these members before you can make sense of them. More specifically, you need to find out the minimum and maximum values for each axis of movement that you’re interested in checking. For example, if you want to see if the joystick has been moved left, you first need to find out the range of values for the x axis of the joystick. You can then use this range to see how far left the joystick handle is being pushed, if at all. You can determine the ranges of joystick axes by calling the Win32 joyGetDevCaps() function. This function fills a JOYCAPS structure with more information about a joystick than you’ll probably ever want to know. For that reason, I won’t go into all the details of the JOYCAPS structure. Instead, I’d like to focus on how to use it to determine the range of the two primary axes, x and y. Following is a code snippet that determines the center point of the x and y axis, which reveals the ranges of each: JOYCAPS jcCaps; joyGetDevCaps(JOYSTICKID1, &jcCaps, sizeof(JOYCAPS)); DWORD dwXCenter = ((DWORD)jcCaps.wXmin + jcCaps.wXmax) / 2; DWORD dwYCenter = ((DWORD)jcCaps.wYmin + jcCaps.wYmax) / 2; The minimum and maximum values for the x axis are wXmin and wXmax, whereas the y axis is

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