Re: Flickerproblem on some machines

"David Ching" <>
Tue, 15 Jan 2008 09:13:25 -0800
"AliR (VC++ MVP)" <AliR@online.nospam> wrote in message

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.

Yes, that is the reason for the flicker. But if he moves the code to
alphablend the rect from OnDraw() into OnEraseBkgnd(), then double-buffering
can be avoided.

-- David

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