作者：徐景周

在放大或縮小圖像時，如何能最好的保持圖像原態比例來顯示呢？下面提供一個涵數可幫你來實現，調用它后，返回的矩形區域既為最佳顯示圖像大小。

l         涵數中的第一個參數rcScreen為圖像要被顯示的矩形大小，第二個參數sizePicture為圖像自身大小，第三個參數bCenter為是否居中顯示，返回值CRect既為圖像最佳顯示大小。

涵數如下所示：

CRect RectSizeWithConstantRatio( CRect* rcScreen,
                                       CSize sizePicture,
                                       BOOL bCenter)
{
  CRect rect(rcScreen);
  double dWidth = rcScreen->Width();
  double dHeight = rcScreen->Height();
  double dAspectRatio = dWidth/dHeight;

  double dPictureWidth = sizePicture.cx;
  double dPictureHeight = sizePicture.cy;
  double dPictureAspectRatio = dPictureWidth/dPictureHeight;

  //If the aspect ratios are the same then the screen rectangle
  // will do, otherwise we need to calculate the new rectangle

  if (dPictureAspectRatio > dAspectRatio)
  {
    int nNewHeight = (int)(dWidth/dPictureWidth*dPictureHeight);
    int nCenteringFactor = (rcScreen->Height() - nNewHeight) / 2;
    rect.SetRect( 0,
                  nCenteringFactor,
                  (int)dWidth,
                  nNewHeight + nCenteringFactor);

  }
  else if (dPictureAspectRatio < dAspectRatio)
  {
    int nNewWidth =  (int)(dHeight/dPictureHeight*dPictureWidth);
    int nCenteringFactor = (rcScreen->Width() - nNewWidth) / 2;
    rect.SetRect( nCenteringFactor,
                  0,
                  nNewWidth + nCenteringFactor,
                  (int)(dHeight));
  }

  return rect;
};


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