Re: OnEraseBkgd

"AliR \(VC++ MVP\)" <AliR@online.nospam>
Mon, 11 Jun 2007 09:51:15 -0500
You shouldn't give up entirely Joe, It can be done

You just have to know what to do to get rid of the garbage left behind when
you hit delete.

void CTransparentEdit::OnKeyDown(UINT nChar, UINT nRepCnt, UINT nFlags)
   CEdit::OnKeyDown(nChar, nRepCnt, nFlags);

void CTransparentEdit::OnKeyUp(UINT nChar, UINT nRepCnt, UINT nFlags)
   CEdit::OnKeyUp(nChar, nRepCnt, nFlags);

LRESULT CTransparentEdit::OnSetText(WPARAM wParam,LPARAM lParam)
   LRESULT Res = Default();
   return Res;

void CTransparentEdit::InvalidateParent()
   CWnd *pParent = GetParent();
   if (pParent)
      CRect Rect;


"Joseph M. Newcomer" <> wrote in message

See below...
On Fri, 8 Jun 2007 15:13:25 -0500, "AliR \(VC++ MVP\)"
<AliR@online.nospam> wrote:

If you are returing a pink brush from WM_CTRLCOLOR then it is doing
what you are telling it to do. You might want to return an instance of
NULL_BRUSH or HOLLOW_BRUSH instead. Also you probably want to call the

Unless Vista has made changes, doing SetBkMode(TRANSPARENT) is a disaster.
To test the
consequences, reposition the caret to the first character, hit the delete
key, and type
another character. In the past, at least through XP, this resulted in

Let me add that creating a transparent edit control is not a trivial task,
you will have to redraw the entire screen everytime there is backspace or
delete, anytime things have moved around using the scrollbars. There
reason you will have to handle these things is that WM_ERASEBKGND is not
sent when these things happen, well neither is WM_PAINT for that matter.
These things happen internaly deep in windows.

I agree. I've seen a number of projects give up on this entirely; my own
inclination is
to not waste time with it. There are more serious problems to solve in
most programs, and
transparent edit controls do not rank high on the list of issues that need
to be addressed
most of the time.

Take a look at this:

This code has a few bugs in it, if you run his test app type something
longer than then window, and try to scroll back you will see why you will
need to repaint.

I just remembered one that I wrote


"David Webber" <> wrote in message

I am going totally mad here.

I have a class CStrEdit derived from CEdit.

I have an instance as a member of my CView derived class, which I use to
edit text "in place" on the CView. It should be effectively
So I arrange for it to contain the same chunk of text which is in the
CView, and this week's method is to give the CStrEdit class a member

CBitmap *ee-pBmpBgd;

In OnShowWindow(), this bitmap is created as a copy of the rectangle of
the CView over which my CStrEdit sits. The idea is that OnEraseBkgnd
should blit the bitmap on the CStrEdit making it look just like the
underneath! As a debugging device I have also given it an HBRUSH
in a nice distinctive pink colour and return it in response to

A I step through OnEraseBkgnd (appended), it steps through the call to
base class and the bitmap drawing code and nothing happens on my view
window. Then at some time after OnEraseBkgnd has happened, the pink
rectangle appears - but no bitmap! [The bitmap is correct - I have
it in a debugging dialogue in passing in order to check!]

I have been changing the code a lot trying to work this out. Earlier I
was using a slightly different method and it worked, but it failed as
as I started using CommonControls6. I feel it should be obvious what
going on but ta the moment I'm baffled. Any ideas?

David Webber
Author of 'Mozart the Music Processor'
For discussion/support see

BOOL CStrEdit::OnEraseBkgnd( CDC* pDC )
BOOL bResult = TRUE;

if( ee_pBmpBkgd && ee_pBmpBkgd->GetSafeHandle() )
    // Call the base class which should draw
    // with the brush....

     bResult = CEdit::OnEraseBkgnd( pDC );

     // There's a bitmap, so use that on top:

     CRect Rect;

     int cx = Rect.Width();
     in t cy = Rect.Height();
     CDC MemDC;
     CBitmap *pOldBmp = MemDC.SelectObject( ee_pBmpBkgd );
     pDC->BitBlt( 0, 0, cx, cy, &MemDC, 0, 0, SRCCOPY );
     MemDC.SelectObject( pOldBmp );

     bResult = TRUE;
     bResult = CEdit::OnEraseBkgnd( pDC );

return bResult;

Joseph M. Newcomer [MVP]
MVP Tips:

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