Re: Flickerproblem on some machines

"AliR \(VC++ MVP\)" <AliR@online.nospam>
Tue, 15 Jan 2008 17:28:27 GMT
"David Ching" <> wrote in message

"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

But if the header is drawn on top of something that is drawn in OnPaint then
he will compeletly miss that if he does his drawing in OnEraseBkgnd and the
end result will look funny.


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