case WM_PAINT: 
        hdc = BeginPaint(hWnd, &ps); 
        // TODO: 在此添加任意绘图代码... 
        //画正玄线 
        #define  PI 3.1415926 
        #define SEGMENT 500 
        int cxClient,cyClient; 
        RECT rect; 
 
        ::GetClientRect(hWnd, &rect); 
        cxClient = rect.right - rect.left; 
        cyClient = rect.bottom - rect.top; 
 
        POINT   pt[SEGMENT]; 
        for (int i=0;i<SEGMENT;i++) 
        { 
            pt[i].x = i * cxClient/SEGMENT;  //cxClient的长度被分成SEGMENT份 
            pt[i].y =  (int)((cyClient/2)*(1 - sin(2 * PI * i/SEGMENT))); //因为sin(2pi)取反，因为数学坐标Y轴向上，而系统中坐标Y轴向下，+cyClient/2是将坐标原点移到左上角 
        } 
        ::Polyline(hdc, pt, SEGMENT); //绘图函数 
 
        EndPaint(hWnd, &ps); 
        break;