win32实现简单的动画

    在许多画图的程序中,大家可以拖动一个图形.其实,实现这个比较简单.只是不断的重画就可以达到预期的效果.windows是基于消息时间的系统.当我们按下左键时,便激发一个WM_LBUTTONDOWN的消息,移动鼠标时,便激发一个WM_MOUSEMOVE的消息,松开鼠标时,也会激起一个WM_LBUTTONUP的消息.所以,当我们拖动一个图形时,可以在移动鼠标时,记住图形的位置.然后使该区域无效,实现重画.我们现在就实现一个可以拖动的圆形动画.为了更好的记住圆形的位置.我们设置一个类型为CPoint的m_pointLeftTop变量.以记住鼠标左上角的坐标.设置一个类型为CSize的m＿sizecircle，用来记住图形的大小．设置一个类型为ＢＯＯＬ的m＿bcaptured的变量，用来标识鼠标是否按下．在试图类的构造函数里．初始化这些变量.代码如下：
   CMyView::CMyVi ():m_sizeEllipse(100,-100);
    m_PointTopLeft(0,0);
    m_sizeOffset(0,0)
    {
            m_bCaptured = FALSE;
    }
    然后分别添加鼠标消息．WM_LBUTTONDOWN,WM_LBUTTONUP,WM_MOUSEMOVE．首先，在左键按下的鼠标消息里，先判断点击点是否在我们的圆形区域里．如果是，则计算点击点到图形左上角的偏移量．代码如下：
    CMyView::OnLButtonDown(UINT nFlags,CPoint point)
    {
        CRect rectEllipse(m_pointTopLeft,m_sizeEllipse);
        CRgn circle;
        CClientDC dc(this);
        OnPrepareDC(&dc);
        dc.LpToDp(rectEllipse);
        circle.CreateEllipseRgnIndirect(rectEllipse);
        if(circle.PtInRegion(point))
        {
                SetCapture();
                m_bCaptured = TRUE;
                CPoint pointTopLeft(m_pointTopLeft);
                dc.LpToDp(&pointTopLeft);
                m_sizeOffset = point - pointTopLeft;
                
                SetCursor(LoadCursor(NULL,IDC_CROSS));
        
        }    

        在ＷＭ＿LBUTTONUP事件中添加如下代码．
        CMyView::OnLButtonUp(UINT nFlag,CPoint point)'
        {
                if(m_Captured)
                {
                        ReleaseCapture();
                        m_Catpured = TRUE;
                }
        }
        在WM_MOUSEMOVＥ事件中添加如下代码：
         CMYView::OnMouseMove(UINT nFlag,CPoint point)
        {
                if(m_Captured)
                {
                        CClientDC dc(this);
                        OnPrepareDC(&dc);
                        CRect rectOld(m_pointLeftTop,m_sizeEllipse);
                        InvalidateRect(rectOld,TRUE);

                        m_pointTopLeft = point - m_sizeOffset;
                        dc.DpToLp(&m_pointTopLeft);
                        CRect  rectNew(m_pointTopLeft,m_sizeEllipse);
                        dc.LptoDP(rectnew);
                        
                        InvalidateRect(rectNew,TRUE);
                
                }
        }

        最后在OnDraw函数，重新画圆：
        pDC->Ellipse(CRect(m_pointTopLeft,m_sizeEllipse));
        整个过程基本上实现了．有的地方需要整理点。．