[Mesa-dev] Support for EXT/ARB_geometry_shader4

[Bryan Cain]

Some of you already know about this from IRC, but recently I've been
working on adding support for GL_EXT_geometry_shader4 and
GL_ARB_geometry_shader4 (which are essentially identical) to Mesa.  A
significant amount of the required code was already there from Zack
Rusin's work on geometry shaders about 2 years ago (before the new GLSL
compiler was merged), so the bulk of my changes are adding support to
the GLSL compiler and glsl_to_tgsi, which is still not a small task.

Anyway, as of yesterday, all of the GLSL demos in mesa/demos that use
EXT/ARB_geometry_shader4 are working fully in my branch with softpipe. 
There are still some things that need doing and/or fixing before it
should be considered for merging into master, but for now, my geometry
shader work (including future updates) can be found in a branch of my
Mesa repository on GitHub at:
https://github.com/Plombo/mesa/tree/geometry-shaders .

It's worth noting that geometry shaders in GL 3.2 (GLSL 1.50) core are
slightly different than the geometry shaders in the EXT and ARB
extensions.  However, the main change in the core version is a change in
the way inputs are accessed which is rather TGSI-unfriendly, so when
GLSL 1.50 is implemented, we will have to lower GS inputs to the
extension way of doing things.  So all of this code is in fact necessary
for GL 3.2 core even though it only implements the extensions.

-Bryan