Indefinido até agora….

Today, I updated KDE4 sources from SVN, and when everything was built, I tried to execute it inside Xephyr, as i always do. But it crashed.·

“Maybe something is broken in SVN”, I thought. But it was not the case. So I started investing what could be.·

The error was:

kwin(1080)/kdecore (KLocale) KLocalePrivate::initEncoding: Defaulting to ISO 8859-1 encoding.
kwin(1080) KWin::Extensions::init: Extensions: shape: 0x “11″ composite: 0x “4″ render: 0x “a” fixes: 0x “40″
kwin: Fatal IO error: client killed

So, I checked that Kwin crashed trying to enable Compositing support. And that reminded me of a post this week by Rivo Laks[1] in planetkde.org talki
ng about automatic compositing detection in kwin. That could be the problem. Then I started reading kwin’s code…

First I thought: “Maybe XComposite is crashing kwin”, so I commented the code that checks for XComposite support, and it was disabled. Then
Kwin started to work! “But Xephyr supports XComposite, and maybe that’s not the problem”. Then I contacted Rivo in IRC, explained the pro
blem, and we started investing further. He said to put some kDebug()s inside the GLX detection code, but Xephyr “insisted” that it had GLX support, and continued crashing.

Xephyr’s documentation says that it doesn’t support GLX, so why does it returned true to that:

compositingprefs.cpp
113 #ifdef HAVE_OPENGL
114 has_glx = glXQueryExtension( display(), &dummy, &dummy );
115 #endif

and crashes here:

kwinglobals.cpp
128 return glXMakeCurrent( display(), mGLWindow, mGLContext ) && !handler.error( true );

A simple glxinfo inside Xephyr crashes it too. Can anyone explain why Xephyr “fakes” that it supports GLX when it doesn’t? Weird…

So, if you have the same problems running kde4 and Xephyr, disable GLX extension:

Xephyr -ac :1 -extension GLX -host-cursor -screen 1024×768

P.S.: I know that there are some patches that implement “real” GLX support in Xephyr, but it’s not the case here. The Xephyr packages in de
bian sid doesn’t have the patches, AFAIK.

[1]:  http://rivolaks.blogspot.com/2007/09/kwin-improvements.html