Step 2: Defining the Action Map

Next, each game action should be assigned to at least one virtual control or device object. These controls are defined as action-mapping constants and are defined by genre and subgenre. In this case, the best choice is the Space Combat subgenre of the flight-games genre. This subgenre makes the following constants available.

Priority 1 controls are those controls that, at the minimum, should be mapped to a device object if possible. Priority 2 controls are less critical to basic game operation and may be mapped as needed.

Game actions are assigned to action-mapping constant controls in an array of DIACTION structures. Each DIACTION structure contains at least one game action, its associated action-mapping constant, any necessary flags, and either a friendly name or identifier (ID) string for the action. The remaining DIACTION members are not used at this point. The following code sample shows definition of the array of DIACTION structures.

#define NUMBER_OF_ACTIONS 18

DIACTION g_rgGameAction[NUMBER_OF_ACTIONS] =
{
    // Device input pre-defined by DirectInput, according to genre
    {INPUT_LEFTRIGHT_AXIS, DIAXIS_SPACESIM_LATERAL, 0, "Turn",},
    {INPUT_UPDOWN_AXIS, DIAXIS_SPACESIM_MOVE, 0, "Move",},
    {INPUT_FIREWEAPONS, DIBUTTON_SPACESIM_FIRE, 0, "Shoot",},
    {INPUT_ENABLESHIELD, DIBUTTON_SPACESIM_GEAR, 0, "Shield",},
    {INPUT_DISPLAYGAMEMENU, DIBUTTON_SPACESIM_DISPLAY, 0, "Display",},
    {INPUT_QUITGAME, DIBUTTON_SPACESIM_MENU, 0, "Quit Game",},

    // Keyboard input mappings
    {INPUT_TURNLEFT, DIKEYBOARD_LEFT, 0, "Turn left", },
    {INPUT_TURNRIGHT, DIKEYBOARD_RIGHT, 0, "Turn right", },
    {INPUT_FORWARDTHRUST, DIKEYBOARD_UP, 0, "Forward thrust", },
    {INPUT_REVERSETHRUST, DIKEYBOARD_DOWN, 0, "Reverse thrust", },
    {INPUT_FIREWEAPONS, DIKEYBOARD_F, 0, "Fire weapons", },
    {INPUT_ENABLESHIELD, DIKEYBOARD_S, 0, "Enable shields", },
    {INPUT_DISPLAYGAMEMENU, DIKEYBOARD_D, DIA_APPFIXED, 
                                      "Display game menu"), },
    {INPUT_QUITGAME, DIKEYBOARD_ESCAPE, DIA_APPFIXED, "Quit game", },

    // Mouse input mappings
    {INPUT_LEFTRIGHT_AXIS, DIMOUSE_XAXIS, 0, "Turn", },
    {INPUT_UPDOWN_AXIS, DIMOUSE_YAXIS, 0, "Move", },
    {INPUT_FIREWEAPONS, DIMOUSE_BUTTON0, 0, "Fire weapons", },
    {INPUT_ENABLESHIELD, DIMOUSE_BUTTON1, 0, "Enable shields", },
};

A DIACTIONFORMAT structure is then initialized to contain the DIACTION array g_rgGameAction defined above. The DIACTIONFORMAT structure also defines the genre, buffer size, axis scaling, and a friendly name for the action map. The g_AppGuid value is a globally unique identifier (GUID) defined in the application to identify the action map. For more information about creating GUIDs, see GUIDs.

DIACTIONFORMAT diaf;
diaf.dwSize        = sizeof(DIACTIONFORMAT);
diaf.dwActionSize  = sizeof(DIACTION);
diaf.dwDataSize    = NUMBER_OF_ACTIONS * sizeof(DWORD);
diaf.dwNumActions  = NUMBER_OF_ACTIONS;
diaf.guidActionMap = g_AppGuid;
diaf.dwGenre       = DIVIRTUAL_SPACESIM;
diaf.rgoAction     = g_rgGameAction;
diaf.dwBufferSize  = 16;
diaf.lAxisMin      = -100;
diaf.lAxisMax      = 100;
diaf.tszActionMap  = "DI Test";

This DIACTIONFORMAT structure is matched against enumerated devices to find the best match in Step 3: Mapping Actions to Devices.