Erasing lines

erm i have read through all the post about erasing line.. and this is what i did...

After i draw the line, a dialog appear and after OnOk,
i set SetROP2 to R2_NOP and draw the line in same position.. but the line is still there. I have tried a number of flags for the SetROP2 but it has no effect.

I even tried to create a CPen with same background color and draw the line, it doesn works either.

Anyone knows where do i go wrong?

Have you invalidated the region or rect you want updated? Also, if you are creating an ActiveX control you should call FireViewChange( ) to update.

i have tried but the line is still seen. ;(

Post your code may be helpful.

Hi,


I have done a similar thing using either:

SetROP2(R2_NOTXORPEN)
or
SetROP2(R2_XORPEN)

You should call this before you draw the line both times. You will also need to set the pen color first.

Does that work for you?
If not, please post your code as suggested.

thanks,
Em

Code:

---

void CtestView::OnMouseMove(UINT nFlags, CPoint point)
{
        if (move)
        {
                CClientDC ClientDC (this);
                ClientDC.SetROP2(R2_NOTXORPEN);

                DrawLine(&ClientDC, start_point, point);
        }
}

---

start_point stores the point on mousedown

Code:

---

void DrawLine(CDC *pDC, CPoint m_pOne, CPoint m_pTwo)
{
        pDC->MoveTo(m_pOne);
        pDC->LineTo(m_pTwo);
}

---

on mouseup, i call a dialog.DoModal()....

Code:

---

void CLineDialog::OnOK()
{
        CDialog::OnOK();
        CDC *pDC = GetDC();
        pDC->SetROP2(R2_NOTXORPEN);

        CPen Pen;
        Pen.CreatePen(PS_SOLID,1,RGB(255,255,255));
        pDC->SelectObject(&Pen);

        pDC->MoveTo(pt_x1, pt_y1);
        pDC->LineTo(pt_x2, pt_y2);
}

---

pt_x1 ... etc is global variable which i store the point.x and point.y on both mousedown and mouseup....

where did i make mistake??

Thanks a lot..

Well, you are drawing to the dialog's DC using GetDC() - that' can't possibly work... :rolleyes:

!! how do i get the CView dc? or should i draw at OnDraw ;\

Quote:

---

Originally posted by ayumi
!! how do i get the CView dc? or should i draw at OnDraw ;\

---

Yes. Always and only in OnDraw().

but i have tried doing so in OnDraw and i do a Invalidate() after the CDialog::OnOK(); .. the line is still there ........ :(

Anyone has any better ideas??

Thanks.

Quote:

---

Originally posted by ayumi
but i have tried doing so in OnDraw and i do a Invalidate() after the CDialog::OnOK(); .. the line is still there ........ :(

---

You mean, you moved the entire code of drawing from OnOk to OnDraw and it still doesn't work ?

BTW, I like your signature...
0 errors, 0 warnings... so funny :)

There should be no need to redraw the line using R2_NOTXORPEN after the dialog is closed. Basically, you erase / draw the line in OnMouseMove(), giving a rubber banding effect while the mouse is moved. On MouseUp, you display the dialog. When the dialog is closed, you call Invalidate(). Now OnDraw() will be called, where you redraw your data - without the line.

i'm not sure why.. even if i don't redraw the lines, after onok, i do a Invalidate(); , the line is still seen -_- it didn erase my background, or how should i erase the background? ;\

Normally, you don't need to do extra background erasing (but you can by implementing a WM_ERASEBKGND handler). There seems to be something else wrong with your code. Can you post the code for

• your view's class definition from the .h file,
• your implementation of OnDraw(),
• the place where you call Invalidate()?

Code:

---

class CtestView : public CView
{
       
protected: // create from serialization only
       
        DECLARE_DYNCREATE(CtestView)

// Attributes
public:
        CtestView();
        CtestDoc* GetDocument();
// Operations
public:

// Overrides
        // ClassWizard generated virtual function overrides
        //{{AFX_VIRTUAL(CtestView)
        public:
        virtual void OnDraw(CDC* pDC);  // overridden to draw this view
        virtual BOOL PreCreateWindow(CREATESTRUCT& cs);
        virtual void OnInitialUpdate();
        protected:
        virtual BOOL OnPreparePrinting(CPrintInfo* pInfo);
        virtual void OnBeginPrinting(CDC* pDC, CPrintInfo* pInfo);
        virtual void OnEndPrinting(CDC* pDC, CPrintInfo* pInfo);
        //}}AFX_VIRTUAL

// Implementation
public:
              virtual ~CtestView();
#ifdef _DEBUG
        virtual void AssertValid() const;
        virtual void Dump(CDumpContext& dc) const;
#endif

protected:
// Generated message map functions
protected:
        //{{AFX_MSG(CtestView)
                afx_msg BOOL OnEraseBkgnd(CDC* pDC);
                afx_msg void OnLButtonDown(UINT nFlags, CPoint point);
        afx_msg void OnLButtonUp(UINT nFlags, CPoint point);
        afx_msg void OnMouseMove(UINT nFlags, CPoint point);
        afx_msg BOOL OnSetCursor(CWnd* pWnd, UINT nHitTest, UINT message);
        afx_msg void OnRButtonDown(UINT nFlags, CPoint point);
        //}}AFX_MSG
        DECLARE_MESSAGE_MAP()
};

---

Code:

---

void CtestView::OnMouseMove(UINT nFlags, CPoint point)
{
        if (move)
        {
                CClientDC ClientDC (this);
                ClientDC.SetROP2(R2_NOTXORPEN);

                DrawLine(&ClientDC, start_point, point);
        }

        CView::OnMouseMove(nFlags, point);
}

---

Code:

---

void DrawLine(CDC *pDC, CPoint m_pOne, CPoint m_pTwo)
{
        pDC->MoveTo(m_pOne);
        pDC->LineTo(m_pTwo);
}

---

Code:

---

void CtestView::OnLButtonUp(UINT nFlags, CPoint point)
{
          CLineDialog dlg;
          dlg.DoModal();

          CView::OnLButtonUp(nFlags, point);
}

---

Code:

---

void CLineDialog::OnOK()
{
        CDialog::OnOK();
        EraseLine = true;
        Invalidate();
}

---

Code:

---

void CtestView::OnDraw(CDC* pDC)
{
          CtestDoc* pDoc = GetDocument();
          ASSERT_VALID(pDoc);
          if(EraseLine)
          {
                CPen Pen;
                Pen.CreatePen(PS_SOLID,1,RGB(0,0,100));
                pDC->SelectObject(&Pen);

                pDC->MoveTo(pt_x1, pt_y1);
                pDC->LineTo(pt_x2, pt_y2);
                EraseLine = false;
          }
          ......
          ......
          //Code to draw back image... too long to post.

---

any errors in my code anyone?? ;(

~~~

////
CPoint m_ptCur;//initialize it in OnLButtonDown(...)
// in your case : start_point = m_ptCur = point;
/////////////////

void CtestView::OnMouseMove(UINT nFlags, CPoint point)
{
if (move)
{
CClientDC ClientDC (this);
ClientDC.SetROP2(R2_NOT);

DrawLine(&ClientDC, start_point, m_ptCur);

DrawLine(&ClientDC,start_point,point);

m_ptCur = point;

}

CView::OnMouseMove(nFlags, point);
}

try

huh?? what does that do??

Quote:

---

Originally posted by ayumi
huh?? what does that do??

---

The code icewater posted correctly implements rubberbanding (it draws the line twice using R2_NOT, once to erase the old line, and once to draw the new one).

The code you posted, in contrast, contains only one MoveTo/LineTo call in OnMouseMove. Furthermore, you still have a MoveTo/LineTo call in OnDraw. Why?

i have tried with and without moveto lineto in OnDraw.. its still the same...i can't remove the old line but after i minimise and maximise the window its gone.

i can't remove it from the background. if its on image, i redraw the image and its gone. but some part is still visible which is out of range of the image. ;(

Well, you are calling Invalidate() from CLineDialog::OnOK(). That will invalidate the dialog, not the view...

then after the user click on ok, where should i Invalidate()?

Either after DoModal() returns (which would be the better place anyway) or from inside the dialog (but then, you need to call it in OnCancel too, not only OnOK). However, the important thing is that you call your view's Invalidate(), not the dialog's.

how can i call the view Invalidate()?? after DoModal() returns i call a Invalidate() it would be the view's invalidate?

Quote:

---

Originally posted by ayumi
how can i call the view Invalidate()?? after DoModal() returns i call a Invalidate() it would be the view's invalidate?

---

OK, let's get to the basics. CView and CDialog are both derived from CWnd, so they both inherit CWnd::Invalidate(). Likewise, your classes CtestView and CLineDialog inherit the same method. Your view is an instance of CtestView. Your dialog (dlg) is an instance of CLineDialog. So when you call Invalidate() from within a method of CtestView (like OnLButtonUp), your call will affect the view. If you call it from a method of CLineDialog (like OnOK), it will affect the dialog. In order to call the view's Invalidate() from the dialog, you will need a reference or pointer to the instance of your view (there are several ways to get that) and then call something pMyView->Invalidate(). And of course, when calling Invalidate() from OnLButtonUp() after DoModal() returns, you will invalidate the view: OnLButtonUp() is a method of your view. Note that this is very elementary C++ stuff, it has nothing to do with MFC or Windows.

Thanks a lot to all.. i have done my Invalidate() at mouseup and it works without having to redraw..

thanKs aLL!~