[PATCH xserver] composite: Inhibit window background paint with manual subwindow redirection

[Ville Syrjälä]

On Wed, Jul 20, 2011 at 05:06:24PM -0400, Owen Taylor wrote:
> On Wed, 2011-07-20 at 10:44 -0400, Owen Taylor wrote:
> > On Wed, 2011-07-20 at 02:54 +0300, Ville Syrjälä wrote:
> > 
> > > BTW I noticed afterwards that this doesn't help all apps. Evince, for
> > > example, still blinks whenever I bring up the popup menu while in
> > > fullscreen mode, whereas Firefox doesn't blink. I did some quick
> > > protocol tracing and I saw some window background mode changes from
> > > the client. A quick look at gdk-x11 code revealed that it does some
> > > tricks with the window background. I never got around to testing if
> > > removing that code would make Evince blink-free (tm).
> > 
> > Interesting... there are certainly tricks being played there, but it's
> > hard to see why they would cause blinking.
> [...]
> > The only thing I can think of is that evince might be changing it's size
> > when popping up the menu, but that seems pretty strange. Hard to guess
> > at without a live situation to debug.
> 
> I did actually have to see it live to figure out what was going on ...
> but once I saw it, and thought about it a bit, I was able to avoid
> digging out the debugger.
> 
> What's going on is that for a window with a non-None background, the
> copying between the parent pixmap and the composite pixmap that we do
> isn't sufficient - all that copying is doing is making sure that things
> _look_ right initially - it doesn't actually suppress expose event
> generation and the background painting that happens during expose event
> generation.

The pointless expose events were supposed to be eliminated by another
patch set [1]. At least my test app [2] manages to redirect/unredirect
non-None windows w/o generating unnecessary expose events.

[1] http://lists.x.org/archives/xorg-devel/2011-April/021450.html
[2] http://gitorious.org/vsyrjala/xwindow_check

-- 
Ville Syrjälä
syrjala at sci.fi
http://www.sci.fi/~syrjala/