1、使用区域绘制图形：

       CBrush *oldbrush;

       CBrush  brush(RGB(0,0,0));

       oldbrush=pDC->SelectObject(&brush);

 

       CRgn rgn1,rgn2;

       rgn1.CreateEllipticRgn(150,150,350,350);//画大圆，圆心(250，250)，半径100

       rgn2.CreateEllipticRgn(100,100,340,340);

       rgn1.CombineRgn(&rgn1,&rgn2,RGN_DIFF);

       pDC->FrameRgn(&rgn1,&brush,2,2);

       pDC->SelectObject(&oldbrush);