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Re: Redisplay problems?

From: Eli Zaretskii
Subject: Re: Redisplay problems?
Date: Mon, 24 Mar 2014 21:34:15 +0200

> From: Stefan <address@hidden>
> Cc: David Kastrup <address@hidden>, address@hidden
> Date: Mon, 24 Mar 2014 14:15:00 -0400
> > OTOH, when we need to deiconify a frame, or expose a large portion of
> > it, I see no space for significant optimizations anyway.  Redisplay
> > optimizations are about redrawing as small portions of the frame as
> > possible.  But in the case in point, we basically need to redraw the
> > entire frame -- how much can you win here anyway?
> Of course, the window-system may elect to do some of this redraw on its
> own by keeping a copy of the frame's last content (under X11 the
> corresponding feature is called "BackingStore").  In that case we don't
> need to redraw the entire frame.  We may often not need to redraw
> anything at all.

Not redrawing anything is easy, provided that we know we can.

> IIRC this "BackingStore" option is typically disabled nowadays in X11,
> so we shouldn't pay too much attention to it.  But I'm not sure how
> compositing window-managers behave in this respect, since they kind of
> "naturally" have a kinf of backing-store.  IOW, if we want to be serious
> about this discussion, we should first get some real data from w32,
> Gnome, and ns cases to see if in practice, a deiconifiy is almost always
> followed by an "expose" of the frame, or not.

I already looked on w32: when a frame is deiconified, we always get a
WM_PAINT message telling us to repaint the whole frame, which I guess
is the Windows equivalent of the Expose event.

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