基于WTL 双缓冲(double buffer)绘图的分析详解

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;
};

void DoPaint(CDCHandle dc, RECT& rect)
{
 CRect rc(rect);
 dc.FillSolidRect(&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);
}