Re: OnEraseBkgd

"AliR \(VC++ MVP\)" <AliR@online.nospam>
Fri, 8 Jun 2007 15:13:25 -0500
If you are returing a pink brush from WM_CTRLCOLOR then it is doing exactly
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 dc's

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.

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 transparent.
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 CView
underneath! As a debugging device I have also given it an HBRUSH member
in a nice distinctive pink colour and return it in response to

A I step through OnEraseBkgnd (appended), it steps through the call to the
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 drawn
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 soon
as I started using CommonControls6. I feel it should be obvious what is
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;

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