Handling the DRV_OPEN and DRV_CLOSE Messages

The following code fragment illustrates the routines the sample device driver uses to handle the DRV_OPEN and DRV_CLOSE messages. This device driver supports only one instance of each video channel.

PCHANNEL NEAR PASCAL VideoOpen(LPVIDEO_OPEN_PARMS lpOpenParms)
{
    PCHANNEL            pChannel;
    LPDEVICE_INIT       lpDI = &devInit;
    LPDWORD             lpdwError = &lpOpenParms->dwError;
    DWORD               dwFlags = lpOpenParms->dwFlags;

    // We're passed a DevNode in the VIDEO_OPEN_PARMS, which we'll pass
    // down to the VxD.  This is really only needed when multiple 
    // instances of identical hardware are installed, and we want to 
    // let the application select which instance to use.
    // The VxD must then compare the DevNode passed in with its internal
    // list of DevNodes and use the corresponding hardware.

    lpDI->dnDevNode = lpOpenParms->dnDevNode;

    //
    //  if this is the very first open then init the hardware.
    //
    AuxDebugEx (2, DEBUGLINE "VideoOpen, RefCount = %d\r\n", gwDriverUsage);

    *lpdwError = DV_ERR_OK;

    // Only initalize the first time opened
    if (!fDeviceInitialized) {

        // Acquire use of the capture hardware
        if (!(AcquireVXP500( gpVxDEntry, &devInit ))) {
            D1("AcquireFailed");
            *lpdwError = DV_ERR_NOTDETECTED;
        }

        // Perform hardware initialization
        if (!HardwareInit(lpDI)) {
            *lpdwError = DV_ERR_NOTDETECTED;
            return NULL;
        }

        ConfigGetSettings();   // Get global hue, sat, channel, zoom.

        if (ConfigInit(lpDI)) {
            if (TransInit()) {  // Allocate the YUV conversion tables
                *lpdwError = DV_ERR_NOMEM;
            } else
                fDeviceInitialized = TRUE;
        } else
            *lpdwError = DV_ERR_NOMEM;

        if (*lpdwError != DV_ERR_OK) {
            TransFini();
            HardwareFini();
            return NULL;
        }
    } // end if this is the first open.

    // get instance memory
    pChannel = (PCHANNEL)LocalAlloc (LPTR, sizeof(CHANNEL));
    if (pChannel == NULL)
        return (PCHANNEL) NULL;

    //
    //  make sure the channel is not already in use
    //
    switch (dwFlags & 
        (VIDEO_EXTERNALIN | VIDEO_EXTERNALOUT | VIDEO_IN | VIDEO_OUT)) {

    case VIDEO_EXTERNALIN:
        if (gwCaptureUsage >= MAX_CAPTURE_CHANNELS)
            goto error;
        gwCaptureUsage++;
        break;

    case VIDEO_EXTERNALOUT:
        if ( gwDisplayUsage >= MAX_DISPLAY_CHANNELS)
            goto error;
        gwDisplayUsage++;
        break;

    case VIDEO_IN:
        if ( gwVideoInUsage >= MAX_IN_CHANNELS)
            goto error;
        gwVideoInUsage++;
        break;

    case VIDEO_OUT:
        if ( gwVideoOutUsage >= MAX_OUT_CHANNELS)
            goto error;
        gwVideoOutUsage++;
        break;

    default:
        goto error;
    }

    //
    // Now that the hardware is allocated init our instance struct.
    //
    pChannel->fccType = OPEN_TYPE_VCAP;
    pChannel->dwOpenType = (dwFlags
        &(VIDEO_EXTERNALIN | VIDEO_EXTERNALOUT | VIDEO_IN | VIDEO_OUT));
    pChannel->dwOpenFlags = dwFlags;
    pChannel->lpVHdr = NULL;
    pChannel->dwError = 0L;

    gwDriverUsage++;
    return pChannel;

error:
    if (pChannel)
        LocalFree((HLOCAL)pChannel);

    *lpdwError = DV_ERR_ALLOCATED;
    return NULL;
}

The following example shows the function used to close the example video capture device driver:

DWORD NEAR PASCAL VideoClose(PCHANNEL pChannel)
{
    // Decrement the channel open counters
    switch (pChannel->dwOpenType) {

    case VIDEO_EXTERNALIN:
        gwCaptureUsage--;
        break;

    case VIDEO_EXTERNALOUT:
        gwDisplayUsage--;
        break;

    case VIDEO_IN:
        // If started, or buffers in the queue,
        // don't let the close happen
        if (gfVideoInStarted || lpVHdrFirst)
            return DV_ERR_STILLPLAYING;
        gwVideoInUsage--;
        break;

    case VIDEO_OUT:
        gwVideoOutUsage--;
        break;

    default:
        break;
    }

    gwDriverUsage--;        // Decrement overall driver useage count.

    if (gwDriverUsage == 0) {
        HardwareFini();        // Shut down the device.
        TransFini();           // Free translation tables.
        ReleaseVXP500( gpVxDEntry, &devInit );
        fDeviceInitialized = FALSE;
    }

    // Free the instance data.
    LocalFree((HLOCAL)pChannel);
    return DV_ERR_OK;
}