VC中如何等比例缩放图像

作者： 徐景周/未来工作室
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。 　　 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; }; ? 此涵数的使用方法如下： { ……(部分省略) //得到屏幕大小 CRect rcScreen( 0, 0, GetSystemMetrics(SM_CXSCREEN), GetSystemMetrics(SM_CYSCREEN)); //得到图像尺寸 CSize sizePicture(picture.m_Width, picture.m_Height); CRect rcNewPictureRect = SizeRectWithConstantAspectRatio(&rcScreen, sizePicture, TRUE); picture.Show(&dc, rcNewPictureRect); }