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;