hey,

i've been playing around with geometry shaders in my spare time and finally got 
them to a basically working state. "basically working" implies a high 
likelihood of many bugs, but bugs that i'd like to get fixed for 7.7 or the 
very latest 7.8. so i'd like to merge arb_geometry_shaders4  as soon as 
possible to master.

it's quite a huge diff, weighting at many thousands lines of code (30000+ but 
that includes the auto-generated api code) because it affects many parts of 
mesa. fortunately the no-geometry-shader paths should stay exactly the same 
and so the execution of those should be completely unchanged after the patch 
lands. the only driver which implements geometry shading right now is the 
gallium software driver, all other drivers work exactly as they have been 
working.

as mentioned geometry shading software support is only implemented in gallium 
(in the draw module along the vertex shading). while the old mesa paths 
obviously have the all the infrastructure work done to be able to implement 
geometry shading, personally i just won't bother with it.

having said that there's a few bugs that i know about, some of them harder 
than the others, in particular:
- support for adjoining primitives is currently busted
- sampling in the geometry shader probably doesn't work (to be honest i 
haven't yet tested it, but i doubt that it's working since the textures come 
in a multi-dimensional array and we don't handle that right yet)
- we don't switch around primitives in the draw module (that's pretty trivial 
to fix, meaning that if input to geometry shader is gl_points, but output is 
gl_triangle_strip we don't actually do that)
- the linking code in st_program.c and st_atom_shader.c is very fragile. 
that's not necessarily a bug but that code is getting way too complex.
- cleanups. i got some debugging output/code left in there.

in general though none of those should be too difficult to fix, but it'd be a 
good idea to figure out if we want geometry shaders in 7.7 or 7.8. 
as always with large patches that touch a lot of the code, keeping up to date 
with master is becoming a bit of an issue which is why i'd like to have the 
merge plan nailed down sooner rather than later.

z

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