如何等比例缩放图像

作者：徐景周

 

在放大或缩小图像时，如何能最好的保持图像原态比例来显示呢？下面提供一个涵数可帮你来实现，调用它后，返回的矩形区域既为最佳显示图像大小。

l         涵数中的第一个参数rcScreen为图像要被显示的矩形大小，第二个参数sizePicture为图像自身大小，第三个参数bCenter为是否居中显示，返回值CRect既为图像最佳显示大小。

涵数如下所示：

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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