[DirectShow] 화면 원본 비율유지

by digipine posted Oct 29, 2017
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비디오 화면 크기를 조정할 때 원본 비율을 유지하고 싶을 때가 많이 있습니다.
그럴때는 아래의 방법을 사용하시면 쉽게 해결 할 수 있습니다.
DirectShow (dsshowutil.h/cpp)에서 제공하는 원본 비율유지 구현 소스입니다.


///////////////////////////////////////////////////////////////////////
// Name: LetterBoxRect
// Desc: Find the largest rectangle that fits inside rcDest and has
//       the specified aspect ratio.
//
// aspectRatio: Desired aspect ratio
// rcDest:      Destination rectangle (defines the bounds)
// prcResult:   Pointer to a RECT struct. The method fills in the
//              struct with the letterboxed rectangle.
//
///////////////////////////////////////////////////////////////////////
HRESULT LetterBoxRect(const SIZE &aspectRatio, const RECT &rcDest, RECT *prcResult)
{
    if (prcResult == NULL)
    {
        return E_POINTER;
    }

    // Avoid divide by zero (even though MulDiv handles this)
    if (aspectRatio.cx == 0 || aspectRatio.cy == 0)
    {
        return E_INVALIDARG;
    }

    LONG width, height;

    LONG SrcWidth = aspectRatio.cx;
    LONG SrcHeight = aspectRatio.cy;
    LONG DestWidth = rcDest.right - rcDest.left;
    LONG DestHeight = rcDest.bottom - rcDest.top;


    if (MulDiv(SrcWidth, DestHeight, SrcHeight) <= DestWidth)
    {
        // src width / src height <= dest width / dest height
        // Letterbox along the sides. ("pillarbox")
        width = MulDiv(DestHeight, SrcWidth, SrcHeight);
        height = DestHeight;
    }
    else
    {
        // src width / src height > dest width / dest height
        // Letterbox along the top and bottom.
        width = DestWidth;
        height = MulDiv(DestWidth, SrcHeight, SrcWidth);
    }

    if (width == -1 || height == -1)
    {
        // MulDiv caught an overflow or divide by zero)
        return E_FAIL;
    }

    assert(width <= DestWidth);
    assert(height <= DestHeight);

    // Fill in the rectangle
    prcResult->left = rcDest.left + ((DestWidth - width) / 2);
    prcResult->right = prcResult->left + width;
    prcResult->top = rcDest.top + ((DestHeight - height) / 2);
    prcResult->bottom = prcResult->top + height;

    return S_OK;
}

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