[Mesa-dev] [PATCH 3/5] glsl: Mark gl_ViewportIndex and gl_Layer varyings as flat.

[Kenneth Graunke]

On Monday, October 26, 2015 02:10:29 PM Ilia Mirkin wrote:
> On Mon, Oct 26, 2015 at 2:03 PM, Kenneth Graunke <kenneth at whitecape.org> wrote:
> > Integer varyings need to be flat qualified - all others were already.
> > I think we just missed this.  Presumably some hardware passes this via
> > sideband and ignores attribute interpolation, so no one has noticed.
> >
> > Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
> > Cc: Chris Forbes <chrisf at ijw.co.nz>
> > ---
> >  src/glsl/builtin_variables.cpp | 39 ++++++++++++++++++++++++++-------------
> >  1 file changed, 26 insertions(+), 13 deletions(-)
> >
> > diff --git a/src/glsl/builtin_variables.cpp b/src/glsl/builtin_variables.cpp
> > index a6ad105..07aacd4 100644
> > --- a/src/glsl/builtin_variables.cpp
> > +++ b/src/glsl/builtin_variables.cpp
> > @@ -887,16 +887,22 @@ builtin_variable_generator::generate_uniforms()
> >  void
> >  builtin_variable_generator::generate_vs_special_vars()
> >  {
> > +   ir_variable *var;
> > +
> >     if (state->is_version(130, 300))
> >        add_system_value(SYSTEM_VALUE_VERTEX_ID, int_t, "gl_VertexID");
> >     if (state->ARB_draw_instanced_enable)
> >        add_system_value(SYSTEM_VALUE_INSTANCE_ID, int_t, "gl_InstanceIDARB");
> >     if (state->ARB_draw_instanced_enable || state->is_version(140, 300))
> >        add_system_value(SYSTEM_VALUE_INSTANCE_ID, int_t, "gl_InstanceID");
> > -   if (state->AMD_vertex_shader_layer_enable)
> > -      add_output(VARYING_SLOT_LAYER, int_t, "gl_Layer");
> > -   if (state->AMD_vertex_shader_viewport_index_enable)
> > -      add_output(VARYING_SLOT_VIEWPORT, int_t, "gl_ViewportIndex");
> > +   if (state->AMD_vertex_shader_layer_enable) {
> > +      var = add_output(VARYING_SLOT_LAYER, int_t, "gl_Layer");
> > +      var->data.interpolation = INTERP_QUALIFIER_FLAT;
> 
> Not that I *strongly* prefer this, but what we'd do in nouveau/codegen
> code (and is IMHO more concise):
> 
> add_output(VARYING_SLOT_LAYER, int_t, "gl_Layer")
>    ->data.interpolation = INTERP_QUALIFIER_FLAT;
> 
> Alternatively, you could just solve this in add_output which should
> automatically set the flat interpolation for int types...
> 
> FTR I don't strongly prefer either of the above to your solution, just
> wanted to point out some alternatives in case you like them more.

Yeah, I've never been a huge fan of using -> on pointers directly
returned by function calls...but that's mostly just personal preference.

I considered having add_input/add_output automatically detect ivec*
types and automatically set things to FLAT.  The nice thing about that
is that would prevent future mistakes.  However, I think ivec* typed
VS inputs/FS outputs shouldn't be marked FLAT, so we might need a
parameter (or special vs_input/fs_output functions)...which seemed
potentially ugly.

I suppose adding a non-optional interp qualifier parameter would also
prevent future mistakes, at the cost of making the common case wordy.

In the end I figured I'd do this for now and let somebody more
inspired tidy it up...
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