CDC的所有成员函数都以逻辑坐标作为参数，而CWnd的成员函数都以设备坐标作为参数，所以要画出正确的图像需要进行坐标转换，本代码给了详细的说明-CDC all member functions are logical coordinates as a parameter, and a member of CWnd equipment functions are to coordinate as a parameter, there is a need to draw a correct imag