在VMR-9的预览中叠加GDI的绘制

DShow采集如何与VMR-9预览结合起来参考上一篇文章。要在VMR-9预览上叠加GDI的绘图，需要自己创建一个BITMAP，把东西在BITMAP上都画好了，再使用IVMRMixerBitmap9::SetAlphaBitmap叠加上去

    hr = m_pVmrWc->QueryInterface(IID_IVMRMixerBitmap9, (LPVOID *)&m_pBmp);
......

HRESULT CDShowDevStream::DrawLine()
{
    HWND hwnd;
    HDC dc, dcMem;
    RECT rc;
    HBITMAP bmpMem;
    HGDIOBJ bmpOld;

    hwnd = (HWND)param_.window.info.win.hwnd;

    dc = ::GetDC(hwnd);
    dcMem = ::CreateCompatibleDC(dc);

    ::GetClientRect(hwnd, &rc);

    bmpMem = ::CreateCompatibleBitmap(dc, rc.right, rc.bottom);
    bmpOld = ::SelectObject(dcMem, bmpMem);

    // Draw a line on bitmap
    HPEN pen = CreatePen(PS_SOLID, 1, RGB(255, 255, 255));
    HPEN oldPen = (HPEN)SelectObject(dcMem, pen);

    MoveToEx(dcMem, 0, 0, NULL);
    LineTo(dcMem, 100, 150);
    SelectObject(dcMem, oldPen);
    DeleteObject(pen);

    VMR9AlphaBitmap bmpInfo;
    ZeroMemory(&bmpInfo, sizeof(bmpInfo));
    bmpInfo.dwFlags = VMRBITMAP_HDC;
    bmpInfo.hdc = dcMem;

    // Show the entire bitmap in the video image.
    SetRect(&bmpInfo.rSrc, 0, 0, rc.right, rc.bottom);
    // rDest specifies the destination rectangle in composition space (0.0f to 1.0f)
    bmpInfo.rDest.left = 0.f;
    bmpInfo.rDest.top = 0.f;
    bmpInfo.rDest.right = 1.0f;
    bmpInfo.rDest.bottom = 1.0f;

    // Set the COLORREF so that the bitmap outline will be transparent
    bmpInfo.dwFlags |= VMRBITMAP_SRCCOLORKEY;
    bmpInfo.clrSrcKey = RGB(0, 0, 0);

    // Set the transparency value (1.0 is opaque, 0.0 is transparent).
    bmpInfo.fAlpha = 1.0f;

    HRESULT hr = m_pBmp->SetAlphaBitmap(&bmpInfo);

    // Cleanup.
    ::SelectObject(dcMem, bmpOld);
    ::DeleteObject(bmpMem);
    ::DeleteDC(dcMem);
    ReleaseDC(hwnd, dc);

    return hr;
}

参考
https://msdn.microsoft.com/en-us/library/windows/desktop/dd375479(v=vs.85).aspx
https://stackoverflow.com/questions/3015307/trying-to-make-vmr-9-mixerbitmap-gdi-work
https://www.codeproject.com/Articles/15531/Showing-an-animated-image-over-running-video