int cxDIB = (int) pDoc->GetDibImage()->DIBWidth(lpDIB);
        int cyDIB = (int) pDoc->GetDibImage()->DIBHeight(lpDIB);

// 获取打印页面的水平宽度(象素)
            int cxPage = pDC->GetDeviceCaps(HORZRES);            
            // 获取打印页面的垂直高度(象素)
            int cyPage = pDC->GetDeviceCaps(VERTRES);            
            // 获取打印机每英寸象素数
            int cxInch = pDC->GetDeviceCaps(LOGPIXELSX);
            int cyInch = pDC->GetDeviceCaps(LOGPIXELSY);
            
            // 计算打印图像大小（缩放，根据页面宽度调整图像大小）
            rcDest.top = rcDest.left = 0;
            rcDest.bottom = (int)(((double)cyDIB * cxPage * cyInch)
                    / ((double)cxDIB * cxInch));
            rcDest.right = cxPage;

当中的下面这句话，如何理解，谢谢
rcDest.bottom = (int)(((double)cyDIB * cxPage * cyInch) / ((double)cxDIB * cxInch));