[Mesa-dev] [PATCH v2 2/7] nir/lower_tex: add lowering for texture gradient on cube maps

[Kenneth Graunke]

On Monday, December 12, 2016 2:11:43 PM PST Iago Toral Quiroga wrote:
> This is ported from the Intel lowering pass that we use with GLSL IR.
> The NIR pass only handles cube maps, not shadow samplers, which are
> also lowered for gen < 8 on Intel hardware. We will add support for
> that in a later patch, at which point we should be able to remove
> the GLSL IR lowering pass.
> 
> v2:
> - added a helper to retrieve ddx/ddy parameters (Ken)
> - No need to make size.z=1.0, we are only using component x anyway (Iago)
> ---
>  src/compiler/nir/nir.h           |   5 +
>  src/compiler/nir/nir_lower_tex.c | 265 +++++++++++++++++++++++++++++++++++++++
>  2 files changed, 270 insertions(+)
> 
> diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
> index 544d4ba..600e3d6 100644
> --- a/src/compiler/nir/nir.h
> +++ b/src/compiler/nir/nir.h
> @@ -2394,6 +2394,11 @@ typedef struct nir_lower_tex_options {
>      * of the texture are lowered to linear.
>      */
>     unsigned lower_srgb;
> +
> +   /**
> +    * If true, lower nir_texop_txd on cube maps with nir_texop_txl.
> +    */
> +   bool lower_txd_cube_map;
>  } nir_lower_tex_options;
>  
>  bool nir_lower_tex(nir_shader *shader,
> diff --git a/src/compiler/nir/nir_lower_tex.c b/src/compiler/nir/nir_lower_tex.c
> index ccca59b..da024e2 100644
> --- a/src/compiler/nir/nir_lower_tex.c
> +++ b/src/compiler/nir/nir_lower_tex.c
> @@ -305,6 +305,265 @@ lower_yx_xuxv_external(nir_builder *b, nir_tex_instr *tex)
>  }
>  
>  static void
> +get_ddx_ddy(nir_tex_instr *tex, nir_ssa_def **ddx, nir_ssa_def **ddy)
> +{
> +   for (int i = 0; i < tex->num_srcs; i++) {
> +      switch (tex->src[i].src_type) {
> +      case nir_tex_src_ddx:
> +         *ddx = tex->src[i].src.ssa;
> +         break;
> +      case nir_tex_src_ddy:
> +         *ddy = tex->src[i].src.ssa;
> +         break;
> +      default:
> +         break;
> +      }
> +   }
> +}
> +
> +/*
> + * Emits a textureLod operation used to replace an existing
> + * textureGrad instruction.
> + */
> +static void
> +replace_gradient_with_lod(nir_builder *b, nir_ssa_def *lod, nir_tex_instr *tex)
> +{
> +   /* Check whether we need projector, shadow comparitor or offset */
> +   int comparitor_index = -1;
> +   int projector_index = -1;
> +   int offset_index = -1;
> +   int extra_srcs = 0;
> +   for (int i = 0; i < tex->num_srcs; i++) {
> +      switch (tex->src[i].src_type) {
> +      case nir_tex_src_projector:
> +         projector_index = i;
> +         extra_srcs++;
> +         break;
> +      case nir_tex_src_offset:
> +         offset_index = i;
> +         extra_srcs++;
> +         break;
> +      case nir_tex_src_comparitor:
> +         comparitor_index = i;
> +         extra_srcs++;
> +         break;
> +      default:
> +         break;
> +      }
> +   }

This looks correct now, but I liked Eric's suggestion from last time -
you can actually just do:

   int comparitor_idx = nir_tex_instr_src_index(tex, nir_tex_src_comparitor);
   int projector_idx = nir_tex_instr_src_index(tex, nir_tex_src_projector);
   int offset_idx = nir_tex_instr_src_index(tex, nir_tex_src_offset);

   /* we replace ddx and ddy with a single value: lod */
   int num_srcs = tex->num_srcs - 1;

   nir_ssa_def *dPdx =
      tex->src[nir_tex_src_index(tex, nir_tex_src_ddx)].src.ssa;
   nir_ssa_def *dPdy =
      tex->src[nir_tex_src_index(tex, nir_tex_src_ddy)].src.ssa;

Either way, this series is:
Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>

I don't need to see a third posting - feel free to fix up any last
things before pushing.  Thanks for doing this!
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