Re: Flickerproblem on some machines

"AliR \(VC++ MVP\)" <AliR@online.nospam>
Thu, 17 Jan 2008 16:02:00 GMT
You don't have to use GDI+ to get the snapshot, I would simply use bitblt to
do it (You can mix GDI+ and GDI calls all day)

Once I had to make a control, that before the first time it drow itself it
took a snap shot of what was behind it. Obvoiulsy this has to be done
before the control draws anything, or else what's behind is no longer
visible. Hope this helps:

BOOL CTransparentStatic2::OnEraseBkgnd(CDC* pDC)
   if (m_SnapShotBmp.GetSafeHandle() == NULL)
      CRect Rect;
      CWnd *pParent = GetParent();
      pParent->ScreenToClient(&Rect); //convert our corrdinates to our

      //copy what's on the parents at this point
      CDC *pDC = pParent->GetDC();
      CDC MemDC;
      CBitmap *pOldBmp = MemDC.SelectObject(&m_SnapShotBmp);


"Tom Becker" <Tom_dot_Becker_at_Ziemann_minus_Urban_dot_de> wrote in message

Thank you all for your answers

@Giovanni, @Alir
Your proposal seems to be a good solution.

Can you tell me how to take a "snapshot" of the area behind the
header-rect using gdi+?
I couldn't find anything suitable for this task in the docs.
The content can change because of scrolling, sizing, ... so I need
to update the snapshot.

I've tried your proposal. Unfortunatly it doesn't work for me.
OnEraseBkgnd() gets called, but drawing uses a decrementing alphavalue.
So I only see the drawing of the first step with "no" transparency.

Tom Becker

AliR (VC++ MVP) schrieb:

The reason InvalidateRect is causing a flicker is that when you call
InvalidateRect on a window the window receives a WM_ERASEBKGND message
followed by a WM_PAINT message which causes the window to erase it's
background which is usually just filled with white color, then the
WM_PAINT will paint whatever it is that the window displays you already
have two paintings going on.

As Giovanni have suggested you need to use double buffering. So generally
you will have to take a snapshot of what is going to be behind the
header, before you draw the header, now when you want to draw the header,
instead of calling InvalidateRect, you can simply draw the snapshot on a
memory dc first then draw the header on top of it, and the bitblt the
entire thing on the window.


"Tom Becker" <Tom_dot_Becker_at_Ziemann_minus_Urban_dot_de> wrote in
message news:uoMBOo1VIHA.5596@TK2MSFTNGP05.phx.gbl...


I want to draw a header in an own view that slowly fades out.

My current approach is to start some timers that invalidate a rectangle
and draw the box with some gdi+ functions. See (the simplified) code

On some machines I get a very anoying flicker by using InvalidateRect().
reason is unknown.

Does anyone know a better solution to display some text that is fading

(Btw: I can't use drawing in a custom NC-Area as I get problems with

Tom Becker

void CMyView::OnDraw(CDC* pDC)
  if(m_alphaHeading > 0)
    Gdiplus::Graphics graphics(pDC->m_hDC);

    Gdiplus::SolidBrush brushBG(Gdiplus::Color(m_alphaHeading,
GetRValue(capCol), GetGValue(capCol), GetBValue(capCol)));

    graphics.FillRectangle(&brushBG, m_titleRect);

    //Write some additional text

void CMyView::OnTimer(UINT nIDEvent)

    m_alphaHeading = 255;
    SetTimer(ID_TM_FADE_TITLE, 50, 0);


  if(nIDEvent == ID_TM_FADE_TITLE)
    if(m_alphaHeading == 0)
      InvalidateRect(titleRect, false);



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