virtual void LeftDown(Point p, dword keyflags) {
        SetCapture();
    	pprev = p;
    }	
    
    virtual void MouseMove(Point p, dword keyflags) {
       if(IsCapture()) {
           int dx=p.x-pprev.x;
           int dy=p.y-pprev.y;    
           x_angle_deg += dx;
           y_angle_deg += dy;       
           pprev = p;
           this->Refresh();
       }
    }