//
    // Check the arguments.
    //
    ASSERT(pWidget);

    //
    // Convert the generic widget pointer into a radio button widget pointer.
    //
    pRadio = (tRadioButtonWidget *)pWidget;

    //
    // See if the given coordinates are within the extents of the radio button.
    //
    if((lX >= pWidget->sPosition.sXMin) &&
       (lX <= pWidget->sPosition.sXMax) &&
       (lY >= pWidget->sPosition.sYMin) &&
       (lY <= pWidget->sPosition.sYMax))
    {
        //
        // See if the pointer was just raised and this radio button is not
        // selected.
        //
        if((ulMsg == WIDGET_MSG_PTR_UP) &&
           !(pRadio->usStyle & RB_STYLE_SELECTED))
        {
            //
            // Loop through the sibblings of this radio button widget.
            //
            for(pSibling = pWidget->pParent->pChild; pSibling;
                pSibling = pSibling->pNext)
            {
                //
                // Skip this widget if it is not a radio button widget, or if
                // it is the original radio button widget.
                //
                if((pSibling == pWidget) ||
                   (pSibling->pfnMsgProc != RadioButtonMsgProc))
                {
                    continue;
                }

                //
                // Convert the generic widget pointer into a radio button
                // widget pointer.
                //
                pRadio2 = (tRadioButtonWidget *)pSibling;

                //
                // See if the sibling radio button is selected.
                //
                if(pRadio2->usStyle & RB_STYLE_SELECTED)
                {
                    //
                    // Clear the selected state of the sibling radio button.
                    //
                    pRadio2->usStyle &= ~(RB_STYLE_SELECTED);

                    //
                    // Redraw the sibling radio button.
                    //
                    RadioButtonPaint(pSibling, 1);

                    //
                    // If there is an OnChange callback for the sibling radio
                    // button then call the callback.
                    //
                    if(pRadio2->pfnOnChange)
                    {
                        pRadio2->pfnOnChange(pSibling, 0);
                    }
                }
            }

            //
            // Set the selected state of this radio button.
            //
            pRadio->usStyle |= RB_STYLE_SELECTED;

            //
            // Redraw the radio button.
            //
            RadioButtonPaint(pWidget, 1);

            //
            // If there is an OnChange callback for this widget then call the
            // callback.
            //
            if(pRadio->pfnOnChange)
            {
                pRadio->pfnOnChange(pWidget, 1);
            }
        }

        //
        // These coordinates are within the extents of the radio button widget.
        //
        return(1);
    }

    //
    // These coordinates are not within the extents of the radio button widget.
    //
    return(0);
}

//*****************************************************************************
//
//! Handles messages for a radio button widget.
//!
//! \param pWidget is a pointer to the radio button widget.
//! \param ulMsg is the message.
//! \param ulParam1 is the first parameter to the message.
//! \param ulParam2 is the second parameter to the message.
//!
//! This function receives messages intended for this radio button widget and
//! processes them accordingly.  The processing of the message varies based on
//! the message in question.
//!
//! Unrecognized messages are handled by calling WidgetDefaultMsgProc().
//!
//! \return Returns a value appropriate to the supplied message.
//
//*****************************************************************************
long
RadioButtonMsgProc(tWidget *pWidget, unsigned long ulMsg,
                   unsigned long ulParam1, unsigned long ulParam2)
{
    //
    // Check the arguments.
    //
    ASSERT(pWidget);

    //
    // Determine which message is being sent.
    //
    switch(ulMsg)
    {
        //
        // The widget paint request has been sent.
        //
        case WIDGET_MSG_PAINT:
        {
            //
            // Handle the widget paint request.
            //
            RadioButtonPaint(pWidget, 0);

            //
            // Return one to indicate that the message was successfully
            // processed.
            //
            return(1);
        }

        //
        // One of the pointer requests has been sent.
        //
        case WIDGET_MSG_PTR_DOWN:
        case WIDGET_MSG_PTR_MOVE:
        case WIDGET_MSG_PTR_UP:
        {
            //
            // Handle the pointer request, returning the appropriate value.
            //
            return(RadioButtonClick(pWidget, ulMsg, ulParam1, ulParam2));
        }

        //
        // An unknown request has been sent.
        //
        default:
        {
            //
            // Let the default message handler process this message.
            //
            return(WidgetDefaultMsgProc(pWidget, ulMsg, ulParam1, ulParam2));
        }
    }
}

//*****************************************************************************
//
//! Initializes a radio button widget.
//!
//! \param pWidget is a pointer to the radio button widget to initialize.
//! \param pDisplay is a pointer to the display on which to draw the push
//! button.
//! \param lX is the X coordinate of the upper left corner of the radio button.
//! \param lY is the Y coordinate of the upper left corner of the radio button.
//! \param lWidth is the width of the radio button.
//! \param lHeight is the height of the radio button.
//!
//! This function initializes the provided radio button widget.
//!
//! \return None.
//
//*****************************************************************************
void
RadioButtonInit(tRadioButtonWidget *pWidget, const tDisplay *pDisplay, long lX,
                long lY, long lWidth, long lHeight)
{
    unsigned long ulIdx;

    //
    // Check the arguments.
    //
    ASSERT(pWidget);
    ASSERT(pDisplay);

    //
    // Clear out the widget structure.
    //
    for(ulIdx = 0; ulIdx < sizeof(tRadioButtonWidget); ulIdx += 4)
    {
        ((unsigned long *)pWidget)[ulIdx / 4] = 0;
    }

    //
    // Set the size of the radio button widget structure.
    //
    pWidget->sBase.lSize = sizeof(tRadioButtonWidget);

    //
    // Mark this widget as fully disconnected.
    //
    pWidget->sBase.pParent = 0;
    pWidget->sBase.pNext = 0;
    pWidget->sBase.pChild = 0;

    //
    // Save the display pointer.
    //
    pWidget->sBase.pDisplay = pDisplay;

    //
    // Set the extents of this radio button.
    //
    pWidget->sBase.sPosition.sXMin = lX;
    pWidget->sBase.sPosition.sYMin = lY;
    pWidget->sBase.sPosition.sXMax = lX + lWidth - 1;
    pWidget->sBase.sPosition.sYMax = lY + lHeight - 1;

    //
    // Use the radio button message handler to processage messages to this
    // radio button.
    //
    pWidget->sBase.pfnMsgProc = RadioButtonMsgProc;
}

//*****************************************************************************
//
// Close the Doxygen group.
//! @}
//
//*****************************************************************************