[Mesa-dev] [PATCH 3/3] glsl/linker: Adapt flat varying handling in preparation for geometry shaders.

[Ian Romanick]

On 04/06/2013 07:49 PM, Paul Berry wrote:
> When a varying is consumed by transform feedback, but is not used by
> the fragment shader, assign_varying_locations() sets its interpolation
> type to "flat" in order to ensure that lower_packed_varyings never has
> to deal with non-flat integral varyings (the GLSL spec doesn't require
> integral vertex outputs to be flat if they aren't consumed by the
> fragment shader).
>
> A similar situation will arise when geometry shader support is added,
> since the GLSL spec only requires integral vertex shader outputs to be
> flat when they are consumed by the geometry shader.  This patch
                                      ^^^^^^^^
fragment?

> modifies the linker to handle this situation too.
> ---
>   src/glsl/link_varyings.cpp | 30 ++++++++++++++++++++----------
>   1 file changed, 20 insertions(+), 10 deletions(-)
>
> diff --git a/src/glsl/link_varyings.cpp b/src/glsl/link_varyings.cpp
> index 431d8fd..7e90beb 100644
> --- a/src/glsl/link_varyings.cpp
> +++ b/src/glsl/link_varyings.cpp
> @@ -541,7 +541,7 @@ store_tfeedback_info(struct gl_context *ctx, struct gl_shader_program *prog,
>   class varying_matches
>   {
>   public:
> -   varying_matches(bool disable_varying_packing);
> +   varying_matches(bool disable_varying_packing, bool consumer_is_fs);
>      ~varying_matches();
>      void record(ir_variable *producer_var, ir_variable *consumer_var);
>      unsigned assign_locations();
> @@ -621,11 +621,15 @@ private:
>       * it was allocated.
>       */
>      unsigned matches_capacity;
> +
> +   const bool consumer_is_fs;
>   };
>
>
> -varying_matches::varying_matches(bool disable_varying_packing)
> -   : disable_varying_packing(disable_varying_packing)
> +varying_matches::varying_matches(bool disable_varying_packing,
> +                                 bool consumer_is_fs)
> +   : disable_varying_packing(disable_varying_packing),
> +     consumer_is_fs(consumer_is_fs)
>   {
>      /* Note: this initial capacity is rather arbitrarily chosen to be large
>       * enough for many cases without wasting an unreasonable amount of space.
> @@ -672,12 +676,12 @@ varying_matches::record(ir_variable *producer_var, ir_variable *consumer_var)
>         return;
>      }
>
> -   if (consumer_var == NULL) {
> -      /* Since there is no consumer_var, the interpolation type of this
> -       * varying cannot possibly affect rendering.  Also, since the GL spec
> -       * only requires integer varyings to be "flat" when they are fragment
> -       * shader inputs, it is possible that this variable is non-flat and is
> -       * (or contains) an integer.
> +   if (consumer_var == NULL || !consumer_is_fs) {
> +      /* Since this varying is not being consumed by the fragment shader, its
> +       * interpolation type varying cannot possibly affect rendering.  Also,
> +       * since the GL spec only requires integer varyings to be "flat" when
> +       * they are fragment shader inputs, it is possible that this variable is
> +       * non-flat and is (or contains) an integer.
>          *
>          * lower_packed_varyings requires all integer varyings to flat,
>          * regardless of where they appear.  We can trivially satisfy that
> @@ -685,6 +689,11 @@ varying_matches::record(ir_variable *producer_var, ir_variable *consumer_var)
>          */
>         producer_var->centroid = false;
>         producer_var->interpolation = INTERP_QUALIFIER_FLAT;
> +
> +      if (consumer_var) {
> +         consumer_var->centroid = false;
> +         consumer_var->interpolation = INTERP_QUALIFIER_FLAT;
> +      }
>      }
>
>      if (this->num_matches == this->matches_capacity) {
> @@ -979,7 +988,8 @@ assign_varying_locations(struct gl_context *ctx,
>   {
>      const unsigned producer_base = VARYING_SLOT_VAR0;
>      const unsigned consumer_base = VARYING_SLOT_VAR0;
> -   varying_matches matches(ctx->Const.DisableVaryingPacking);
> +   varying_matches matches(ctx->Const.DisableVaryingPacking,
> +                           consumer && consumer->Type == GL_FRAGMENT_SHADER);
>      hash_table *tfeedback_candidates
>         = hash_table_ctor(0, hash_table_string_hash, hash_table_string_compare);
>      hash_table *consumer_inputs
>