[Mesa-dev] [PATCH] glsl: Assign transform feedback varying slots in linker.

[Paul Berry]

On 7 November 2011 18:18, Marek Olšák <maraeo at gmail.com> wrote:

> On Tue, Nov 8, 2011 at 1:13 AM, Paul Berry <stereotype441 at gmail.com>
> wrote:
> > @@ -1806,16 +2187,50 @@ link_shaders(struct gl_context *ctx, struct
> gl_shader_program *prog)
> >         break;
> >    }
> >
> > +   /* From GL_EXT_transform_feedback:
> > +    *   A program will fail to link if:
> > +    *
> > +    *   * the <count> specified by TransformFeedbackVaryingsEXT is
> > +    *     non-zero, but the program object has no vertex or geometry
> > +    *     shader;
> > +    */
> > +   if (prog->TransformFeedback.NumVarying > 0 &&
> > +       prev >= MESA_SHADER_FRAGMENT) {
> > +      linker_error(prog, "Transform feedback varyings specified, but "
> > +                   "no vertex or geometry shader is present.");
> > +      goto done;
> > +   }
> > +
> >    for (unsigned i = prev + 1; i < MESA_SHADER_TYPES; i++) {
> >       if (prog->_LinkedShaders[i] == NULL)
> >         continue;
> >
> > +      tfeedback_decl *tfeedback_decls = NULL;
> > +      unsigned num_tfeedback_decls = 0;
> > +      if (i == MESA_SHADER_FRAGMENT &&
> > +          prog->TransformFeedback.NumVarying != 0) {
> > +         num_tfeedback_decls = prog->TransformFeedback.NumVarying;
> > +         tfeedback_decls = ralloc_array(mem_ctx, tfeedback_decl,
> > +
>  prog->TransformFeedback.NumVarying);
> > +         if (!parse_tfeedback_decls(prog, mem_ctx, num_tfeedback_decls,
> > +
>  prog->TransformFeedback.VaryingNames,
> > +                                    tfeedback_decls))
> > +            goto done;
> > +      }
> > +
> >       if (!assign_varying_locations(ctx, prog,
> >                                    prog->_LinkedShaders[prev],
> > -                                   prog->_LinkedShaders[i])) {
> > +                                   prog->_LinkedShaders[i],
> > +                                    num_tfeedback_decls,
> tfeedback_decls)) {
> >         goto done;
> >       }
> >
> > +      if (i == MESA_SHADER_FRAGMENT) {
> > +         if (!store_tfeedback_info(ctx, prog, num_tfeedback_decls,
> > +                                   tfeedback_decls))
> > +            goto done;
> > +      }
> > +
> >       prev = i;
> >    }
>
> Also I realized that this part won't work if there is no fragment
> shader. Transform feedback varyings should be assigned *regardless* of
> the presence of a fragment shader.
>

Good catch, I forgot to think about that case.  That will require modifying
assign_varying_locations to accept NULL for the consumer, and modifying the
control flow in link_shaders slightly.  I'll post a revised patch shortly.
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