Getting Control Pad Input

This section looks at user interaction with the control pad, discussing the following topics:

• Utility Functions for Using the Control Pad
• The jsanimation.c Example
• The basicslideshow.c Example

All examples in the Jumpstart2 example set use the functions from controlpad.c in the Examples folder, which offers the following utility functions:

• ControlPadSanityCheck-makes sure the event broker has been initialized.
• InitControlPad-connects a task to the event broker for control pad interaction.
• DoControlPad-queries the specified control pad and de-bounces specified key presses
• ReturnPreviousControlPad-returns the state of the controlpad as it is remembered
• KillControlPad-disconnects the task from the event broker and frees resources

The animation example in the Jumpstart2 folder has been simplified to clarify how control pad interaction occurs. The main() function in jsanimation.c contains a loop that continuously calls HandleControlPad(). HandleControlPad() recognizes two button events:

• If the user presses the Start button, the game is over.
• If the user presses Control-A, the explosion is triggered.

kContinuousMask specifies for which buttons continuous presses are allowed.

Example 1: The HandleControlPad function in jsanimation

#define     kContinuousMask     ( ControlA )

int32 HandleControlPad( void )
/*
    Respond to control pad input:
      - The A key is enabled for continuous presses.
      - Start button means quit the program.
      - A button and arrows means fire (explode the cel).
    Returns -1 if the user pressed the start button to quit, otherwise 0.
*/
{
    uint32  controlBits;
    Point   aUFOCenter;
    int32 retValue = 0;

    DoControlPad(1, &controlBits, kContinuousMask );

    if ( controlBits & ControlStart )
/* If the user has pressed the START button, the game is over. */
    {
        retValue = -1;
        goto DONE;
    }
/* ControlA triggers the explosion */
    if ( controlBits & ControlA )
    {
        if ( !gBoomCount )                            /* Don't fire until previous explosion is finished */
        {
            gBoomCount = gExplosionAnim->num_Frames;
                                /* Position center of explosion at center of the UFO */
            aUFOCenter = CalcCCBCenterPoint(gUFO_CCB);
            CenterCCB(gExplosionCCB, aUFOCenter.pt_X, aUFOCenter.pt_Y);
                                /* Get a random center for the next UFO */
            CenterCCB(gUFO_CCB, (Coord) Random(DISPLAY_WIDTH), (Coord)
                                                         Random(DISPLAY_HEIGHT));

        }
    }

DONE:
    return retValue;

}

The jsbasicslideshow.c example uses the same JSGetControlPad() function but a more complex HandleControlPad() function that allows more complex user input.

Note that this example includes controlpad.c and calls InitControlPad() during initialization and KillControlPad() during shutdown.

Example 2: The HandleControlPad function in jsbasicslideshow.c

int32 HandleControlPad( void )
/*
Respond to the user's control pad input.
- Right and down arrows mean show next image in list
- Left and up arrows mean show previous image in list
- Start button means quit the program
- B button means show the other buffer
- C button means toggle automatic display mode
Returns -1 if the user pressed the start button to quit, otherwise 0.
*/
{
    int32 retValue = 0;
    uint32  controlBits;

    DoControlPad(1, &controlBits, 0 ); 
/* no continuous button presses */

/* if the Start button is pressed, the user wants to quit */
    if ( controlBits & ControlStart )
    {
        retValue = -1;
    }

/* if the A button is pressed \xc9  (no action in this interface) */
    else if ( controlBits & ControlA )
    {
        ;
    }

/* if button B is pressed, display the other buffer */
    else if ( controlBits & ControlB )
        {
        gScreenContext->sc_curScreen = 
                                1 - gScreenContext->sc_curScreen;
        }
/* if button C is pressed toggle autoshow */
    else if ( controlBits & ControlC )
        {
        gAutoShowFlag = !gAutoShowFlag;
    
        PRT( ("Auto-show mode is ") );
        if ( gAutoShowFlag )
            {
             PRT( ("TRUE\n") );
             }
        else
            PRT( ("FALSE\n") );
    
        }

    else if ( controlBits & 
        (ControlUp | ControlLeft | ControlDown | ControlRight))
        /* Arrows mean move one image forward or backward */
        {
        if ( controlBits & ControlUp )
            {
            LoadPreviousImage();
            }
        else if ( controlBits & ControlLeft )
            {
            LoadPreviousImage();
            }
        else if ( controlBits & ControlDown )
            {
            LoadNextImage();
            }
        else if ( controlBits & ControlRight )
            {
            LoadNextImage();
            }
    
        }

    return retValue;

}