ClientToScreen( )和ScreenToClient( )

ClientToScreen( )是把窗口坐标转换为屏幕坐标
ScreenToClient( )是把屏幕坐标转换为窗口坐标
屏幕坐标是相对于屏幕左上角的，而窗口坐标是相对于窗口用户区左上角的
VC下，有些函数使用窗口坐标，有些使用屏幕坐标，使用时要分清。


一个窗体分为两部分：系统区和客户区
象标题和菜单之类的是系统区，由系统来控制，客户区就是你的地盘喽！！！
Width, Height 是指整体的，ClientWidth, ClientHeight是指客户区的，两者相减就是
系统区的啦！！！
ClientToScreen是把坐标从当前窗体转化成全屏幕的！！！
ScreenToClient是把屏幕坐标转化成相对当前窗体的坐标！！！！

bool   m_bIsLButtonDawn =false;

void CDrawDlg::OnMouseMove(UINT nFlags, CPoint point)
{
// TODO: Add your message handler code here and/or call default
CWnd *pwnd=GetDlgItem(IDC_EDIT1);
     CDC *pdc=pwnd->GetDC();
CRect rect;
this->ClientToScreen(&point);
pwnd->ScreenToClient(&point);
pwnd->GetClientRect(&rect);

//   HCURSOR hcur=::LoadCursorFromFile("pen.cur");
//   SetClassLong(GetSafeHwnd(),GCL_HCURSOR,(LONG)hcur);  

// CPen pen(PS_INSIDEFRAME,-1,RGB(255,255,255));
//      CPen* olePen=pdc->SelectObject(&pen);
if(rect.PtInRect(point) &&   m_bIsLButtonDawn )
{

   pdc->DPtoLP(&m_fp);
   pdc->MoveTo(m_fp);
   pdc->DPtoLP(&point);
   pdc->LineTo(point);

}
   m_fp=point;
//   pdc->SelectObject(olePen);
ReleaseDC(pdc);
CDialog::OnMouseMove(nFlags, point);
}

void CDrawDlg::OnLButtonUp(UINT nFlags, CPoint point)
{
   m_bIsLButtonDawn =false;
// TODO: Add your message handler code here and/or call default
/**//*
    CWnd *pwnd=GetDlgItem(IDC_EDIT1);
      CDC *pdc=pwnd->GetDC();
   CRect rect;
   this->ClientToScreen(&point);
   pwnd->ScreenToClient(&point);
   pwnd->GetClientRect(&rect);
  
   if(rect.PtInRect(point))
   {
    pdc->DPtoLP(&m_fp);
    pdc->MoveTo(m_fp);
    pdc->DPtoLP(&point);
    pdc->LineTo(point);

   }
   ReleaseDC(pdc);*/

CDialog::OnLButtonUp(nFlags, point);
}

void CDrawDlg::OnLButtonDown(UINT nFlags, CPoint point)
{
// TODO: Add your message handler code here and/or call default
CWnd *pwnd=GetDlgItem(IDC_EDIT1);
CDC *pDC=pwnd->GetDC();
CRect rect;
this->ClientToScreen(&point);
pwnd->ScreenToClient(&point);
pwnd->GetClientRect(&rect);
if(rect.PtInRect(point))
{
   m_fp.x=point.x;
   m_fp.y=point.y;
}
ReleaseDC(pDC);
   m_bIsLButtonDawn =true;
CDialog::OnLButtonDown(nFlags, point);
}