[Mesa-dev] explaining update_arrays

[Brian Paul]

On 06/22/2011 04:18 AM, Dave Airlie wrote:
> I don't suppose anyone could contribute a comment on why somethings
> check ctx->VertexProgram._Current,
> and others check ctx->VertexProgram._Enabled

The former may point to a GLSL shader/program, a 
GL_NV/ARB_vertex_program program or a shader derived from 
fixed-function state.

The later will only be true when a GL_NV/ARB_vertex_program program is 
enabled and valid (GL_VERTEX_PROGRAM_ARB is enabled and the user's 
program compiled successfully).

I haven't looked at all the places where _Enabled or _Current is used, 
but there is a difference in what they mean.


> 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.

Do you suspect a bug here?

I'd have to go back and re-read all the specs to remember the details.

-Brian