Re: Flickerproblem on some machines

From:

Tom Becker <Tom_dot_Becker_at_Ziemann_minus_Urban_dot_de>

Newsgroups:

microsoft.public.vc.mfc

Date:

Thu, 17 Jan 2008 11:12:04 +0100

Message-ID:

<OAqMpFPWIHA.748@TK2MSFTNGP04.phx.gbl>

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.

@David
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.

thx
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.

AliR.

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

Hallo

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
below.

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

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

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

thx
Tom Becker

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

    DWORD capCol = GetSysColor(COLOR_ACTIVECAPTION);
    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)
{
  if(nIDEvent == ID_TM_FADE_TITLE_START)
  {
    KillTimer(ID_TM_FADE_TITLE_START);

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

    return;
  }

  if(nIDEvent == ID_TM_FADE_TITLE)
  {
    if(m_alphaHeading == 0)
      KillTimer(ID_TM_FADE_TITLE);
    else
    {
      m_alphaHeading--;
      InvalidateRect(titleRect, false);
    }

    return;
   }

   CFormView::OnTimer(nIDEvent);
}