[Mesa-dev] [PATCH v2 4/7] nir/lower_tex: add lowering for texture gradient on shadow samplers

[Iago Toral Quiroga]

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.

v2 (Ken):
 - Use the helper function to retrieve ddx/ddy
 - Swizzle away size components we are not interested in
---
 src/compiler/nir/nir.h           |  7 +++++
 src/compiler/nir/nir_lower_tex.c | 56 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 63 insertions(+)

diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
index 600e3d6..27b4fbd 100644
--- a/src/compiler/nir/nir.h
+++ b/src/compiler/nir/nir.h
@@ -2399,6 +2399,13 @@ 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 da024e2..a9370c3 100644
--- a/src/compiler/nir/nir_lower_tex.c
+++ b/src/compiler/nir/nir_lower_tex.c
@@ -564,6 +564,56 @@ 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 */
+   unsigned component_mask;
+   switch (tex->sampler_dim) {
+   case GLSL_SAMPLER_DIM_3D:
+      component_mask = 7;
+      break;
+   case GLSL_SAMPLER_DIM_1D:
+      component_mask = 1;
+      break;
+   default:
+      component_mask = 3;
+      break;
+   }
+
+   nir_ssa_def *ddx, *ddy;
+   get_ddx_ddy(tex, &ddx, &ddy);
+   nir_ssa_def *size =
+      nir_channels(b, get_texture_size(b, tex), component_mask);
+
+   /* 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, ddx, size);
+   nir_ssa_def *dPdy = nir_fmul(b, ddy, size);
+
+   nir_ssa_def *rho;
+   if (dPdx->num_components == 1) {
+      rho = nir_fmax(b, nir_fabs(b, dPdx), nir_fabs(b, dPdy));
+   } else {
+      rho = nir_fmax(b,
+                     nir_fsqrt(b, nir_fdot(b, dPdx, dPdx)),
+                     nir_fsqrt(b, nir_fdot(b, dPdy, dPdy)));
+   }
+
+   /* lod = log2(rho).  We're ignoring GL state biases for now. */
+   nir_ssa_def *lod = nir_flog2(b, rho);
+
+   /* Replace the gradient instruction with an equivalent lod instruction */
+   replace_gradient_with_lod(b, lod, tex);
+}
+
+static void
 saturate_src(nir_builder *b, nir_tex_instr *tex, unsigned sat_mask)
 {
    b->cursor = nir_before_instr(&tex->instr);
@@ -794,6 +844,12 @@ nir_lower_tex_block(nir_block *block, nir_builder *b,
          lower_gradient_cube_map(b, tex);
          progress = true;
       }
+
+      if (tex->op == nir_texop_txd && options->lower_txd_shadow &&
+          tex->is_shadow && tex->sampler_dim != GLSL_SAMPLER_DIM_CUBE) {
+         lower_gradient_shadow(b, tex);
+         progress = true;
+      }
    }
 
    return progress;
-- 
2.7.4