[Mesa-dev] [PATCH 16/28] glsl: don't pack tessellation stages like we do other stages

[Timothy Arceri]

On Tue, 2015-12-29 at 17:38 +1100, eocallaghan at alterapraxis.com wrote:
> On 2015-12-29 16:00, Timothy Arceri wrote:
> > Tessellation shaders treat varyings as shared memory and
> > invocations
> > can access each others varyings therefore we can't use the existing
> > method to lower them.
> > 
> > This adds a check for these stages as following patches will
> > allow explicit locations to be lowered even when the driver and 
> > existing
> > tesselation checks ask for it to be disabled, we do this to enable 
> > support
> > for the component layout qualifier.
> 
> I find this a little hard to read and understand, could you brush it
> up 
> a bit
> please if that's ok?

Sure I'll try again :)


> 
> > ---
> >  src/glsl/lower_packed_varyings.cpp | 62 
> > +++++++++++++++++++++-----------------
> >  1 file changed, 34 insertions(+), 28 deletions(-)
> > 
> > diff --git a/src/glsl/lower_packed_varyings.cpp
> > b/src/glsl/lower_packed_varyings.cpp
> > index 2899846..e4e9a35 100644
> > --- a/src/glsl/lower_packed_varyings.cpp
> > +++ b/src/glsl/lower_packed_varyings.cpp
> > @@ -737,40 +737,46 @@ lower_packed_varyings(void *mem_ctx, unsigned
> > locations_used,
> >                        ir_variable_mode mode, unsigned 
> > gs_input_vertices,
> >                        gl_shader *shader, bool
> > disable_varying_packing)
> >  {
> > -   exec_list *instructions = shader->ir;
> >     ir_function *main_func = shader->symbols->get_function("main");
> >     exec_list void_parameters;
> >     ir_function_signature *main_func_sig
> >        = main_func->matching_signature(NULL, &void_parameters,
> > false);
> > -   exec_list new_instructions, new_variables;
> > -   lower_packed_varyings_visitor visitor(mem_ctx, locations_used, 
> > mode,
> > -                                         gs_input_vertices,
> > -                                         &new_instructions,
> > -                                         &new_variables,
> > -                                         disable_varying_packing);
> > -   visitor.run(shader);
> > -   if (mode == ir_var_shader_out) {
> > -      if (shader->Stage == MESA_SHADER_GEOMETRY) {
> > -         /* For geometry shaders, outputs need to be lowered
> > before 
> > each call
> > -          * to EmitVertex()
> > -          */
> > -         lower_packed_varyings_gs_splicer splicer(mem_ctx, 
> > &new_instructions);
> > -
> > -         /* Add all the variables in first. */
> > -         main_func_sig->body.head->insert_before(&new_variables);
> > 
> > -         /* Now update all the EmitVertex instances */
> > -         splicer.run(instructions);
> > +   if (!(shader->Stage == MESA_SHADER_TESS_CTRL ||
> > +         shader->Stage == MESA_SHADER_TESS_EVAL)) {
> > +      exec_list *instructions = shader->ir;
> > +      exec_list new_instructions, new_variables;
> > +
> > +      lower_packed_varyings_visitor visitor(mem_ctx,
> > locations_used, 
> > mode,
> > +                                            gs_input_vertices,
> > +                                            &new_instructions,
> > +                                            &new_variables,
> > +                                           
> >  disable_varying_packing);
> > +      visitor.run(shader);
> > +      if (mode == ir_var_shader_out) {
> > +         if (shader->Stage == MESA_SHADER_GEOMETRY) {
> > +            /* For geometry shaders, outputs need to be lowered
> > before 
> > each
> > +             * call to EmitVertex()
> > +             */
> > +            lower_packed_varyings_gs_splicer splicer(mem_ctx,
> > +                                                     
> > &new_instructions);
> > +
> > +            /* Add all the variables in first. */
> > +            main_func_sig->body.head
> > ->insert_before(&new_variables);
> > +
> > +            /* Now update all the EmitVertex instances */
> > +            splicer.run(instructions);
> > +         } else {
> > +            /* For other shader types, outputs need to be lowered
> > at 
> > the end
> > +             * of main()
> > +             */
> > +            main_func_sig->body.append_list(&new_variables);
> > +            main_func_sig->body.append_list(&new_instructions);
> > +         }
> >        } else {
> > -         /* For other shader types, outputs need to be lowered at
> > the 
> > end of
> > -          * main()
> > -          */
> > -         main_func_sig->body.append_list(&new_variables);
> > -         main_func_sig->body.append_list(&new_instructions);
> > +         /* Shader inputs need to be lowered at the beginning of 
> > main() */
> > +         main_func_sig->body.head
> > ->insert_before(&new_instructions);
> > +         main_func_sig->body.head->insert_before(&new_variables);
> >        }
> > -   } else {
> > -      /* Shader inputs need to be lowered at the beginning of
> > main() 
> > */
> > -      main_func_sig->body.head->insert_before(&new_instructions);
> > -      main_func_sig->body.head->insert_before(&new_variables);
> >     }
> >  }
> 
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