BufferLock.h

//////////////////////////////////////////////////////////////////////////
//
// THIS CODE AND INFORMATION IS PROVIDED "AS IS" WITHOUT WARRANTY OF
// ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED TO
// THE IMPLIED WARRANTIES OF MERCHANTABILITY AND/OR FITNESS FOR A
// PARTICULAR PURPOSE.
//
// Copyright (c) Microsoft Corporation. All rights reserved.
//
//////////////////////////////////////////////////////////////////////////



#pragma once

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

class VideoBufferLock
{   
    template <class T> void SafeRelease(T **ppT)
    {
        if(*ppT)
        {
            (*ppT)->Release();
            *ppT = NULL;
        }
    }
public:
    VideoBufferLock(IMFMediaBuffer *pBuffer) : m_p2DBuffer(NULL), m_bLocked(FALSE)
    {
        m_pBuffer = pBuffer;
        m_pBuffer->AddRef();

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

    ~VideoBufferLock()
    {
        UnlockBuffer();
        SafeRelease(&m_pBuffer);
        SafeRelease(&m_p2DBuffer);
    }

    //-------------------------------------------------------------------
    // 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 = NULL;

            hr = m_pBuffer->Lock(&pData, NULL, NULL);
            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;
                }
            }
        }

        m_bLocked = (SUCCEEDED(hr));

        return hr;
    }

    //-------------------------------------------------------------------
    // UnlockBuffer
    //
    // Unlocks the buffer. Called automatically by the destructor.
    //-------------------------------------------------------------------

    void UnlockBuffer()
    {
        if (m_bLocked)
        {
            if (m_p2DBuffer)
            {
                (void)m_p2DBuffer->Unlock2D();
            }
            else
            {
                (void)m_pBuffer->Unlock();
            }
            m_bLocked = FALSE;
        }
    }

private:
    IMFMediaBuffer  *m_pBuffer;
    IMF2DBuffer     *m_p2DBuffer;

    BOOL            m_bLocked;
};