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Writing a Generalized Input System: T3DLIB2.CPP

Writing a simple set of wrapper functions around DirectInput is almost a no-brainer. Well, it takes some brains, but for the most part it's fairly easy. All you need to do is create an API with a very simple interface and very few parameters that

  • Initializes the DirectInput system.

  • Sets up and acquires the keyboard, mouse, and joystick (or any subset).

  • Reads data from any of the input devices.

  • Shuts down, unacquires, and releases everything.

I have created such an API, and it's available in T3DLIB2.CPP|H on the CD. The API does everything you need to initialize DirectInput and read any device. However, I didn't do any input merging, as shown in the example a few sections previous. Rather, you will still receive input in terms of standard DirectInput device state(s) structures, and you'll process the various fields within each device state structure (keyboard, mouse, and joystick). However, this gives you the most freedom.

Before reviewing the functions, take a look at Figure 9.15. It depicts the relationship between each device and the data flow.

Figure 9.15. The DirectInput software system.


Here are the globals for the library:

LPDIRECTINPUT8        lpdi;       // dinput object
LPDIRECTINPUTDEVICE8  lpdikey;    // dinput keyboard
LPDIRECTINPUTDEVICE8  lpdimouse;  // dinput mouse
LPDIRECTINPUTDEVICE8 lpdijoy;    // dinput joystick
GUID    joystickGUID; // guid for main joystick
char    joyname[80];  // name of joystick

// all input is stored in these records
UCHAR keyboard_state[256]; // contains keyboard state table
DIMOUSESTATE mouse_state;  // contains state of mouse
DIJOYSTATE joy_state;      // contains state of joystick
int joystick_found;        // tracks if stick is plugged in

Input from the keyboard is placed in keyboard_state[], the mouse data is stored in mouse_state, and the joystick data is stored in joy_state by the input system. The structures of these records are the standard DirectInput device state structures. But in general, the mouse and joystick are roughly equivalent as far as the x,y position goes. That is, you access them via the fields lX and lY, and the buttons are BOOLEANs in rgbButtons[].

Let's get to the functions. The variable joystick_found is a Boolean that is set when you request joystick access. If a joystick is found, it is True; otherwise, it is False. With it, you can conditionally block out code that uses the joystick. So without further ado, here is the new API.

Function Prototype:

int DInput_Init(void);


DInput_Init() initializes the DirectInput input system. It creates the main COM object and returns True if successful, False otherwise. And of course, the global lpdi will be valid. The function does not create any devices, though. Here's an example of initializing the input system:

if (!DInput_Init())
   { /* error */ }

Function Prototype:

void DInput_Shutdown(void);


DInput_Shutdown() releases all the COM objects and any resources allocated during the call to DInput_Init(). Normally, you would call DInput_Shutdown() at the very end of your application, after you have released all the input devices themselves. We'll get to that shortly. Anyway, here's an example of shutting down the input system:


Function Prototype:



DInput_Init_Keyboard() initializes and acquires the keyboard. This should always work and return True, unless another DirectX application has taken over in a really uncooperative way. Here's an example:

if (!DInput_Init_Keyboard())
   { /* error */ }

Function Prototype:

int DInput_Init_Mouse(void);


DInput_Init_Mouse() initializes and acquires the mouse. The function takes no parameters and returns True if successful and False otherwise. But it should always work, unless a mouse isn't plugged in or there's another DirectX application that has totally taken over! If everything goes well, lpdimouse becomes the valid interface pointer. Here's an example:

if (!DInput_Init_Mouse()) { /* error */ }

Function Prototype:

int DInput_Init_Joystick(int min_x=-256, // min x range
                int max_x=256,  // max x range
                int min_y=-256, // min y range
                int max_y=256,  // max y range
                int dead_zone=10); // dead zone in percent


DInput_Init_Joystick() initializes the joystick device for use. The function takes five parameters, which define the X-Y range of motion of the data sent back from the joystick and the dead zone as a percentage. If you want to use the defaults of -256 to 256 and a 10 percent dead zone for each axis, you need not send parameters because they have default values (it's a C++ thing).

If the call returns back a True, a joystick was found and has been set up, initialized, and acquired. After the call, the interface pointer lpdijoy will be valid if you need it for anything. In addition, the string joyname[] will contain the "friendly" name of the joystick device, such as Microsoft Sidewinder Pro and so on.

Here's an example of initializing the joystick and setting its X-Y ranges to -1024 to 1024, with a 5 percent dead zone:

if (!DInput_Init_Joystick(-1024, 1024, -1024, 1024, 5))
   { /* error */ }

Function Prototype(s):

void DInput_Release_Joystick(void);
void DInput_Release_Mouse(void);
void DInput_Release_Keyboard(void);


DInput_Release_Joystick(), DInput_Release_Mouse(), and DInput_Release_Keyboard() release each of those respective input devices when you're done with them. The functions can be called even if you haven't initialized those respective devices, so you can just call them all at the end of your application if you want. Here's a complete example of starting up the DirectInput system, initializing all the devices, and then releasing them and shutting down:

// initialize the DirectInput system

// initialize all input devices and acquire them

// input loop ....do work here
// now done...

// first release all devices, order is unimportant

// shutdown DirectInput

Function Prototype:

int DInput_Read_Keyboard(void);


DInput_Read_Keyboard() scans the keyboard state and places the data in keyboard_state[], which is an array of 256 bytes. This is the standard DirectInput keyboard state array, so you must use the DirectInput key constant DIK_* if you want to make sense of it. If a key is pressed, the array value will be 0x80. Here's an example of testing if the right and left keys are down using the manifest constants in DirectInput (which you can look up in the SDK or the abridged Table 9.4):

// read the keyboard
if (!DInput_Read_Keyboard())
   { /* error */ }

// now test the state data
if (keyboard_state[DIK_RIGHT]
   { /* move ship right */ }
if (keyboard_state[DIK_LEFT]
   { /* move ship left */ }

Function Prototype:

int DInput_Read_Mouse(void);


DInput_Read_Mouse() reads the relative mouse state and stores the result in mouse_state, which is a DIMOUSESTATE structure. The data is in relative delta mode. In most cases you'll only need to look at mouse_state.lX, mouse_state.lY, and rgbButtons[0..2], which are Booleans for the three mouse buttons. Here's an example of reading the mouse and using it to move a cursor around and draw:

// read the mouse
if (!DInput_Read_Mouse())
   { /* error */ }

// move cursor

// test if left button is down
if (mouse_state.rgbButtons[0])

Function Prototype:

int DInput_Read_Joystick(void);


DInput_Read_Joystick() polls the joystick and then reads the data into joy_state, which is a DIJOYSTATE structure. Of course, if there isn't a joystick plugged in, the function returns False and joy_state will be invalid, but you get the idea. If it's successful, joy_state contains the state information of the joystick. The data returned will be in the range you previously set for each axis, and the button values are Booleans in rgbButtons[]. For example, here's how you would use the joystick to move a ship right and left, and use the first button to fire:

// read the joystick data
if (!DInput_Read_Joystick())
    { /* error */ }

// move the ship

// test for trigger
if (joy_state.rgbButtons[0])
   { // fire weapon // }

Of course, your joystick may have a lot of buttons and multiple axes. In that case, you can use the other fields of joy_state as defined in the DIJOYSTATE DirectInput structure.

The T3D Library at a Glance

At this point, you have two main .CPP|H modules that make up the T3D library:

  • T3DLIB1.CPP|H— DirectDraw plus graphics algorithms.

  • T3DLIB2.CPP|H— DirectInput.

Keep this in mind when you're compiling programs. If you want to compile a demo program, call it DEMOX_Y.CPP and then look at its .H includes. If it includes either of the related .H library modules, you'll obviously need to include the .CPP files too.


Make sure to link DDRAW.LIB, DINPUT.LIB and DINPUT8.LIB.

As an example of using the new library functions in T3DLIB2.CPP|H, I have rewritten the three demos created in this chapter, DEMO9_1.CPP, DEMO9_2.CPP, and DEMO9_3.CPP, as DEMO9_1a.CPP (DEMO9_1a_16B.CPP 16-bit version), DEMO9_2a.CPP (DEMO9_2a_16B.CPP 16-bit version), and DEMO9_3a.CPP (DEMO9_3a_16B.CPP 16-bit version), respectively. Therefore, you can see how much code can be chucked out when you use the library functions.

To compile any of the programs, make sure to include both of the library source files, as well as all of the DirectX .LIB files. And please, for God's sake, set your compiler to Win32 .EXE. I have received over 30 emails today from people asking how to set the compiler! I'm a scientist, Jim, not a technical support agent for Microsoft!

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