VC，一条会被鼠标移动的直线

                                        对话框中的小红线可以被移动的

一、类名是 CBinarizationDlg

二、定义两个变量

BOOL m_flag;

int nPos;

在构造函数初始化m_flag = false;nPos=256;

三、响应消息函数三个

afx_msg void OnPaint();

afx_msg void OnLButtonDown(UINT nFlags, CPoint point);

afx_msg void OnLButtonUp(UINT nFlags, CPoint point);

afx_msg void onm ouseMove(UINT nFlags, CPoint point);

四、代码加注释

void CBinarizationDlg::OnPaint()
 {
 CPaintDC dc(this); // device context for painting

 CPhotoMeterDoc* pDoc = (CPhotoMeterDoc*) ((CMainFrame*)AfxGetMainWnd())->GetActiveFrame()->GetActiveDocument();

 CRect rect;
 //GetDlgItem(IDC_STATIC_HISTO)->GetWindowRect(&rect);
 //ScreenToClient(&rect);
 GetDlgItem(IDC_STATIC_HISTO)->GetClientRect(&rect);
 int width = rect.Width();
 int height = rect.Height();

 // Create a memory CDC
 CDC memDC;
 memDC.CreateCompatibleDC( &dc );
 CBitmap bitmap;
 bitmap.CreateCompatibleBitmap( &dc, width, height );
 CBitmap* oldbitmap = memDC.SelectObject( &bitmap );

 memDC.FillSolidRect( rect, RGB( 255, 255, 255 ) );

 CPen axisPen(PS_SOLID,1,RGB(0,0,0));
 CPen* pOldPen = dc.SelectObject(&axisPen);
 memDC.MoveTo(rect.left+5,rect.bottom-4);
 memDC.LineTo(rect.right-5,rect.bottom-4);
 memDC.SelectObject(pOldPen);

 // The frame
 CBrush brh(RGB(0,0,0));
 memDC.FrameRect(&rect,&brh);

 //histogram
 if (pDoc && pDoc->image) {

 if (pDoc->m_hmax){
 int ybase = rect.bottom-5;
 float yratio = (ybase - rect.top)/(float)pDoc->m_hmax;

 CPen grayPen(PS_SOLID, 1, RGB(84, 64, 64));
 pOldPen = memDC.SelectObject(&grayPen);
 //调整的界面刚好使rect.right-rect.left-10是512，即中间横线为512
 for (int x=0 ; x<256; x++)
 {
 memDC.MoveTo(2*x+rect.left+5,ybase);
 memDC.LineTo(2*x+rect.left+5, (int)(ybase-pDoc->m_hgray[x]*yratio));
 }

 memDC.SelectObject(pOldPen);
 }else{
 pDoc->m_hmax=pDoc->GetImage()->Histogram(pDoc->m_hr,pDoc->m_hg,pDoc->m_hb,pDoc->m_hgray);
 if (pDoc->m_hmax) Invalidate();
 }
 }//end of histogram

 CPen redpen(PS_SOLID,0, RGB(222,0,0));
 pOldPen = memDC.SelectObject(&redpen);
 if ((nPos >= rect.left+5) && (nPos < rect.right-5) )
 {
 memDC.MoveTo(nPos,rect.bottom-5);
 memDC.LineTo(nPos,rect.top+4);
 }
 memDC.SelectObject(&pOldPen);

 dc.BitBlt( 10, 10, width, height, &memDC, 0, 0, SRCCOPY );
 memDC.SelectObject( oldbitmap );

 }

 void CBinarizationDlg::OnLButtonDown(UINT nFlags, CPoint point)
 {
 CRect rect;
 GetDlgItem(IDC_STATIC_HISTO)->GetClientRect(&rect);
   rect.left +=5;
   rect.right -=5;
 rect.bottom +=5;

 point.Offset(-10,-10);
 if (rect.PtInRect(point) && (nPos == point.x))
 {
 m_flag = TRUE;
 nPos = point.x ;
 }
 CDialog::OnLButtonDown(nFlags, point);
 }

 void CBinarizationDlg::OnLButtonUp(UINT nFlags, CPoint point)
 {
 m_flag = FALSE;
 Invalidate(FALSE);

 CDialog::OnLButtonUp(nFlags, point);
 }

 void CBinarizationDlg::OnMouseMove(UINT nFlags, CPoint point)
 {
 //CDC *pDC = this->GetDC();
 CRect rect;
 GetDlgItem(IDC_STATIC_HISTO)->GetClientRect(&rect);
 rect.left +=5;
 rect.right -=5;
 rect.bottom +=5;

 point.Offset(-10,-10);
 if (m_flag && rect.PtInRect(point))
 {
 nPos = point.x;
 Invalidate(FALSE);
 }
 CDialog::OnMouseMove(nFlags, point);
 //ReleaseDC(pDC);
 }

说明：IDC_STATIC_HISTO是一个picture控件的ID，visible = false，这个只是用来辅助定位的咚咚咚