WTL-双缓冲（double buffer）绘图

下面创建了一个普通的WTL窗口类，在窗口的客户区中有大量的绘图工作，使用CDoubleBufferImpl类来消除绘图时的闪烁现象：

const COLORREF WHITE_COLOR = RGB(255,255,255);

const COLORREF BLUE_COLOR = RGB(0,0,255);

class CMainWindow :

     public CWindowImpl<CMainWindow,CWindow,CSimpleWinTraits>,

     public CDoubleBufferImpl<CMainWindow>

{

public:

     typedef CMainWindow _thisClass;

     typedef CDoubleBufferImpl<_thisClass> _baseDblBufImpl;

     BEGIN_MSG_MAP(CMainWindow)

             MSG_WM_CREATE(OnCreate)

             MSG_WM_DESTROY(OnDestroy)

             CHAIN_MSG_MAP(_baseDblBufImpl)

     END_MSG_MAP()

  int OnCreate(LPCREATESTRUCT lpCreateStruct)

     {

             m_RectPen.CreatePen(PS_SOLID,1,BLUE_COLOR);

             return 0;

     }

  void OnDestroy()

     {

             PostQuitMessage(0);

     }

     void OnPaint(CDCHandle)

     {

             CPaintDC dc(m_hWnd);

          DoPaint(dc.m_hDC);

     }

  void DoPaint(CDCHandle dc)

     {

             CRect rc;

             GetClientRect(&rc);

             dc.FillRect(&rc,WHITE_COLOR);

          HPEN hOldPen = dc.SelectPen(m_RectPen);

             const int width = 5;

             int x = 0;

             int count = rc.Width()/width;

             int height = 0;

             for (int i=0; i<count; i++)

             {

                     height = (int)((double)rand()*rc.Height())/RAND_MAX;

                     dc.Rectangle(x,rc.Height(),x+width,rc.Height()-height);

                     x += width;

             }

             dc.SelectPen(hOldPen);

     }

  /*

     void DoPaint(CDCHandle dc)

     {

             CRect rc;

             GetClientRect(&rc);

             int width = rc.Width(), height = rc.Height();

          //use GDI+ to draw in the client area

             Graphics g(dc.m_hDC);

             SolidBrush whiteBrush(Color(255,255,255));

             g.FillRectangle(&whiteBrush,0,0,width,height);

          Pen bluePen(Color(0,0,255));

             const int dx = 5;

             int count = width/dx;

             int x = 0, y = 0, h = 0;

             for (int i=0;i<count;i++)

             {

                     h = ((double)rand()*height)/RAND_MAX;

                     g.DrawRectangle(&bluePen,x,y,dx,h);

                     x += dx;

             }

     }

     */

private:

     CPen m_RectPen;

};