[Mesa-dev] [PATCH 4/6] nir/lower_tex: add lowering for texture gradient on shadow samplers

[Eric Anholt]

Kenneth Graunke <kenneth at whitecape.org> writes:

> [ Unknown signature status ]
> On Thursday, December 1, 2016 8:53:19 AM PST Iago Toral Quiroga wrote:
>> This is ported from the Intel lowering pass that we use with GLSL IR.
>> This takes care of lowering texture gradients on shadow samplers other
>> than cube maps. Intel hardware requires this for gen < 8.
>> ---
>>  src/compiler/nir/nir.h           |  7 +++++++
>>  src/compiler/nir/nir_lower_tex.c | 40 ++++++++++++++++++++++++++++++++++++++++
>>  2 files changed, 47 insertions(+)
>> 
>> diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
>> index ed388c6..d494d5f 100644
>> --- a/src/compiler/nir/nir.h
>> +++ b/src/compiler/nir/nir.h
>> @@ -2437,6 +2437,13 @@ typedef struct nir_lower_tex_options {
>>      * If true, lower nir_texop_txd on cube maps with nir_texop_txl.
>>      */
>>     bool lower_txd_cube_map;
>> +
>> +   /**
>> +    * If true, lower nir_texop_txd on shadow samplers (except cube maps)
>> +    * with nir_texop_txl. Notice that cube map shadow samplers are lowered
>> +    * with lower_txd_cube_map.
>> +    */
>> +   bool lower_txd_shadow;
>>  } 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 c7c3db2..d5ea509 100644
>> --- a/src/compiler/nir/nir_lower_tex.c
>> +++ b/src/compiler/nir/nir_lower_tex.c
>> @@ -556,6 +556,40 @@ lower_gradient_cube_map(nir_builder *b, nir_tex_instr *tex)
>>  }
>>  
>>  static void
>> +lower_gradient_shadow(nir_builder *b, nir_tex_instr *tex)
>> +{
>> +   assert(tex->sampler_dim != GLSL_SAMPLER_DIM_CUBE);
>> +   assert(tex->is_shadow);
>> +   assert(tex->op == nir_texop_txd);
>> +   assert(tex->dest.is_ssa);
>> +
>> +   /* Use textureSize() to get the width and height of LOD 0 */
>> +   nir_ssa_def *size = get_texture_size(b, tex);
>> +
>> +   /* Scale the gradients by width and height.  Effectively, the incoming
>> +    * gradients are s'(x,y), t'(x,y), and r'(x,y) from equation 3.19 in the
>> +    * GL 3.0 spec; we want u'(x,y), which is w_t * s'(x,y).
>> +    */
>> +   nir_ssa_def *dPdx = nir_fmul(b, tex->src[2].src.ssa, size);
>> +   nir_ssa_def *dPdy = nir_fmul(b, tex->src[3].src.ssa, size);
>
> NIR texture sources aren't guaranteed to be in any particular order
> (it's kind of annoying)...you should instead do:
>
>     nir_ssa_def *dPdx;
>     nir_ssa_def *dPdy;
>
>     for (unsigned i = 0; i < tex->num_srcs; i++) {
>        switch (tex->src[i].src_type) {
>        case nir_tex_src_ddx:
>           dPdx = nir_fmul(b, tex->src[i].src.ssa, size);
>           break;
>        case nir_tex_src_ddy:
>           dPdy = nir_fmul(b, tex->src[i].src.ssa, size);
>           break;
>        default:
>           break;
>        }
>     }
>
> Same comment on patch two.  Maybe make a get_ddx_ddy() helper?

nir_tex_instr_src_index() helps with this.
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