[Mesa-dev] explaining update_arrays

[Dave Airlie]

>>
>>> By the looks of it the 0/POS attrib + the overlapping/16-31 ones check
>>> _Current
>>> and the others all check _Enabled, to me it would make some sense at
>>> least if 0
>>> was consistent with the others, but maybe someone knows what is correct.
>>
>> The confusion probably goes all the way back to the ARB's unfortunate
>> inability to reconcile NV's vs. ATI's different handling of generic
>> vertex arrays.  NV used aliasing while ATI didn't so the ARB extension
>> made it optional (a mess).  Plus, I think there was some minor
>> difference in GL_ARB_vertex_program vs. GL_ARB_vertex_shaders w.r.t.
>> generic vertex arrays.
>
> In GLSL, only attribute 0 / glVertexArray alias.  The other non-generic
> arrays can only be accessed via the named built-in variables (e.g.,
> gl_Color).

Ah that makes sense, thanks guys,

>
>> Do you suspect a bug here?

No but this codepath is a real dog on profiles, and I'm guessing 90%
of it useless in 90% of profiles,
like in an app that doesn't use VBOs it pretty much could end up as
min = 2*1000*1000*1000; but
to figure that out it has a lot overhead. I'm guessing we should
probably push working out the array max
closer to the edges and not in this path if we can.

So I had to make sure I understood it before I try to change it.

Dave.