设置透明背景

CRect rc;
CPoint pt(0,0);
MapWindowPoints(GetParent(),&pt,1);  获取子窗口在父窗口中的位置
rc.left = pt.x;
rc.top = pt.y;
rc.right = rc.left + rt.Width();
rc.bottom = rc.top + rt.Height();

CxImage smallImg(rc.Width(),rc.Height());//截取的image大小


m_imageBack.Crop(rc,&smallImg);


  smallImg.Draw(dcMem.m_hDC,rt);
pDC->BitBlt(0,0,clientRect.Width(),clientRect.Height(),&dcMem,0,0,SRCCOPY);