Paul Berry authored Jul 31, 2012 and Keith Packard committed Aug 15, 2012

In __glXScreenInit() we generate the set of GLX visuals in two steps:
first we match each pre-existing X visual with a corresponding
FBConfig, then we generate a new X visual to correspond to all the
remaining FBConfigs.

The first step is used for the two default 24-bit visuals (true color
and direct color) and for the 32-bit visual.  If windowsystem
multisampling is enabled in Mesa, we need to ensure that none of these
three visuals gets matched to a multisampled config.

Fixes a bug with windowsystem multisampling in gnome-shell.  If the X
server happens to match up a multisampled FBConfig to the 32-bit
visual, gnome-shell will try to use it to read pixels from
alpha-blended windows (such as gnome-terminal), resulting in no window
appearing on screen.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Chad Versace <chad.versace@linux.intel.com>
Signed-off-by: Keith Packard <keithp@keithp.com>