walkthrough-creating-a-windows-store-app-using-wrl-and-media-foundation_3.h

#pragma once

//  Locks a video buffer that might or might not support IMF2DBuffer.

class VideoBufferLock
{
public:
    VideoBufferLock(IMFMediaBuffer *pBuffer) : m_p2DBuffer(nullptr)
    {
        m_pBuffer = pBuffer;
        m_pBuffer->AddRef();

        // Query for the 2-D buffer interface. OK if this fails.
        m_pBuffer->QueryInterface(IID_PPV_ARGS(&m_p2DBuffer));
    }

    ~VideoBufferLock()
    {
        UnlockBuffer();
        m_pBuffer->Release();
        if (m_p2DBuffer)
        {
            m_p2DBuffer->Release();
        }
    }

    // LockBuffer:
    // Locks the buffer. Returns a pointer to scan line 0 and returns the stride.

    // The caller must provide the default stride as an input parameter, in case
    // the buffer does not expose IMF2DBuffer. You can calculate the default stride
    // from the media type.

    HRESULT LockBuffer(
        LONG  lDefaultStride,    // Minimum stride (with no padding).
        DWORD dwHeightInPixels,  // Height of the image, in pixels.
        BYTE  **ppbScanLine0,    // Receives a pointer to the start of scan line 0.
        LONG  *plStride          // Receives the actual stride.
        )
    {
        HRESULT hr = S_OK;

        // Use the 2-D version if available.
        if (m_p2DBuffer)
        {
            hr = m_p2DBuffer->Lock2D(ppbScanLine0, plStride);
        }
        else
        {
            // Use non-2D version.
            BYTE *pData = nullptr;

            hr = m_pBuffer->Lock(&pData, nullptr, nullptr);
            if (SUCCEEDED(hr))
            {
                *plStride = lDefaultStride;
                if (lDefaultStride < 0)
                {
                    // Bottom-up orientation. Return a pointer to the start of the
                    // last row *in memory* which is the top row of the image.
                    *ppbScanLine0 = pData + abs(lDefaultStride) * (dwHeightInPixels - 1);
                }
                else
                {
                    // Top-down orientation. Return a pointer to the start of the
                    // buffer.
                    *ppbScanLine0 = pData;
                }
            }
        }
        return hr;
    }

    HRESULT UnlockBuffer()
    {
        if (m_p2DBuffer)
        {
            return m_p2DBuffer->Unlock2D();
        }
        else
        {
            return m_pBuffer->Unlock();
        }
    }

private:
    IMFMediaBuffer  *m_pBuffer;
    IMF2DBuffer     *m_p2DBuffer;
};