VC中如何等比例縮放圖像

作者：Future Studio.徐景周
版權所有：徐景周
轉載請聯系作者

　　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，調用它後，返回的矩形區域既為最佳顯示圖像大小。
　　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;
};
 此涵數的使用方法如下：
{
……(部分省略)
//得到屏幕大小
CRect rcScreen( 0, 0,
GetSystemMetrics(SM_CXSCREEN),
GetSystemMetrics(SM_CYSCREEN));

//得到圖像尺寸
CSize sizePicture(picture.m_Width, picture.m_Height);

CRect rcNewPictureRect =
SizeRectWithConstantAspectRatio(&rcScreen,
sizePicture,
TRUE);
picture.Show(&dc, rcNewPictureRect);
}