When using cairo-dock, vlc, smplayer, mythtv and possibly other qt-4 based applications display transparent user interfaces and totally transparent movie player window.
Steps to Reproduce:
1.start cairo-dock -o (it could be that compiz is creating same effect)
2.start vlc/smplayer/mythtv tv output
user interface partially transparent, only sound, movie is invisible (transparent as well)
Normal UI, visible movie
It seems there is a problem with how QT handles (or does not handle) OpenGL context.
Some info is at http://www.x.org/archive/X11R6.8.0/doc/RELNOTES5.html
Workaround is described at http://www.qtforum.org/article/26669/qt4-mess-up-the-opengl-context.html
I can confirm that it works for above mentioned apps.
Easy workaround implementation:
make file /usr/local/bin/qt_alfa_problem
and then make a link, in the same directory,
ln -s qt_alfa_problem vlc
ln -s qt_alfa_problem smplayer
ln -s qt_alfa_problem mythfrontend
Is upstream aware of the issue?
You can make workaround easier: just create file /usr/local/bin/smplayer with:
XLIB_SKIP_ARGB_VISUALS=1 /usr/bin/smplayer "$*"
and make chmod +x for it
This issue must be fixed upstream.