Mixing an Image Onto the Video Window in C++

Microsoft DirectShow 9.0

Mixing an Image Onto the Video Window in C++

This topic applies to Windows XP or later.

This section describes how to display an alpha-blended image over the Video Control's video image. Internally, the Video Control uses the Video Mixing Renderer filter (VMR).

Mixing an IPictureDisp Object

In C++, you can specify the image either as an IPictureDisp object or as a bitmap. The IPictureDisp object is designed for Automation clients, and it is generally easier to work with a bitmap in C++. When you capture an image from the Video Control, however, it returns an IPictureDisp object. Therefore, the first example shows how to use the captured image as the mixing image. The result is to show a "snapshot" of the video in a corner of the window, while the video continues to play in the background.

First, submit a tune request and call the Video Control's IMSVidCtl::Run method. (For more information, see Tuning with the Video Control.)

To capture the image:

Call the IMSVidCtl::get_VideoRendererActive method. This method returns a pointer to the IMSVidVideoRenderer interface on the video renderer device.

Call the IMSVidVideoRenderer::Capture method. This method returns an IPictureDisp object, which contains the image.

Now you can use the IPictureDisp object as the VMR's mixer image, by calling the IMSVidVideoRenderer::SetupMixerBitmap method. The method takes the following parameters:

• The IPictureDisp pointer.
• The desired opacity, expressed as an integer from 0 to 100.
• The position of the image on the video window, specified as an IMSVidRect interface.

The IMSVidRect interface is an Automation-compatible wrapper for a rectangle. The following example retrieves a rectangle by calling IMSVidVideoRenderer::get_MixerBitmap, but then overrides the dimensions of the rectangle. It then captures an image and mixes it onto the video window. For brevity, the example omits any error checking.

CComPtr<IMSVidCtl> m_pVideoControl;  // Video Control
CComPtr<IMSVidVideoRenderer> pVideo; // video renderer device
CComPtr<IPictureDisp> pPic;          // picture object
CComPtr<IMSVidRect> pRect;           // Automation-compatible rectangle
RECT rcWin;

/* Build and run the filter graph (not shown). */

// Capture the image.
hr = m_pVideoControl->get_VideoRendererActive(&pVideo);
hr = pVideo->Capture(&pPic);

// Set the rectangle to 1/4 of the window.
hr = pVideo->get_MixerBitmapPositionRect(&pRect);
::GetWindowRect(GetDlgItem(IDC_MSVIDCTL1), &rcWin);
hr = pRect->put_Width(rcWin.right / 2);
hr = pRect->put_Height(rcWin.bottom / 2);
hr = pRect->put_Top(0);
hr = pRect->put_Left(0);

// Set the mixer bitmap.
long lOpacity = 80;  // 0 = transparent, 100 = opaque 
hr = pVideo->SetupMixerBitmap(pPic, lOpacity, pRect);

The position rectangle defaults to the entire video control window. If you don't want to specify the rectangle, you can use the IMSVidVideoRenderer::put_MixerBitmap and IMSVidVideoRenderer::put_MixerBitmapOpacity methods:

hr = pVideo->put_MixerBitmap(pPic);
hr = pVideo->put_MixerBitmapOpacity(lOpacity);

Mixing a Bitmap

In C++, you can also mix a bitmap that is specified as a DirectDraw surface or as a handle to a GDI object. To do so, use the IMSVidVideoRenderer::put__MixerBitmap method. This method acts as a pass-through to the VMR's IVMRMixerBitmap::SetAlphaBitmap method. As an alternative, you can use the IMSVidVideoRenderer::get__MixerBitmap method to obtain the VMR's IVMRMixerBitmap interface and call SetAlphaBitmap directly.

For more information, see Displaying an Application-Supplied Bitmap on the Composited Image. The example shown here is modified from the example code in that topic.

The following example loads a bitmap resource and displays it in the upper-left corner of the video window, blended at 50% opacity. For brevity, the example omits any error checking.

HRESULT ShowBitmap(IMSVidCtl *pVideoControl, WORD nID)
{ 
    CComPtr<IVMRMixerBitmap> pVmrBitmap;
    CComPtr<IMSVidVideoRenderer> pVideo;
    HRESULT hr = pVideoControl->get_VideoRendererActive(&pVideo);
    hr = pVideo->get__MixerBitmap(&pVmrBitmap);
    if (SUCCEEDED(hr))
    {
        RECT rc;
        HBITMAP hBitmap = LoadBitmap(hInst, MAKEINTRESOURCE(nID));
        ::GetWindowRect(GetDlgItem(IDC_MSVIDCTL1), &rc);
        hr = MixImage(hWnd, pVmrBitmap, hBitmap, rc.right, rc.bottom);
    }
}

HRESULT MixImage(HWND hwndApp, IVMRMixerBitmap* pBmp, HBITMAP hbm,
  long cx, long cy)
{
    HRESULT hr;
    BITMAP bm;
    HBITMAP hbmOld;
    HDC hdc = GetDC(hwndApp);
    HDC hdcBmp = CreateCompatibleDC(hdc);
    ReleaseDC(hwndApp, hdc);

    GetObject(hbm, sizeof(bm), &bm);
    hbmOld = (HBITMAP)SelectObject(hdcBmp, hbm);

    VMRALPHABITMAP bmpInfo;  // Holds information about the bitmap.
    ZeroMemory(&bmpInfo, sizeof(bmpInfo));
    bmpInfo.dwFlags = VMRBITMAP_HDC; // Tells the VMR we are using an HDC.
    bmpInfo.hdc = hdcBmp;

    // The source rectangle is the entire bitmap.
    SetRect(&bmpInfo.rSrc, 0, 0, bm.bmWidth, bm.bmHeight);

    // The target rectangle is the upper left corner of the video image,
    // expressed as a percentage of the image.
    bmpInfo.rDest.left = 0.f;
    bmpInfo.rDest.top = 0.f;
    bmpInfo.rDest.right = static_cast<float>(bm.bmWidth) /
                          static_cast<float>(cx);
    bmpInfo.rDest.bottom = static_cast<float>(bm.bmHeight) /
                           static_cast<float>(cy);
    bmpInfo.fAlpha = 0.5f; // Set the alpha to 50%
    hr = pBmp->SetAlphaBitmap(&bmpInfo);
  
    // Clean up.
    DeleteObject(SelectObject(hdcBmp, hbmOld));
    DeleteDC(hdcBmp);
    return hr;

}