[Mesa-dev] [PATCH 2/3] nir/lower-tex: add srgb->linear lowering

[Rob Clark]

From: Rob Clark <robclark at freedesktop.org>

Signed-off-by: Rob Clark <robclark at freedesktop.org>
---
 src/compiler/nir/nir.h           |  7 ++++++
 src/compiler/nir/nir_lower_tex.c | 46 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 53 insertions(+)

diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
index bbbc208..2c0f705 100644
--- a/src/compiler/nir/nir.h
+++ b/src/compiler/nir/nir.h
@@ -2301,6 +2301,13 @@ typedef struct nir_lower_tex_options {
     * while 4 and 5 represent 0 and 1 respectively.
     */
    uint8_t swizzles[32][4];
+
+   /**
+    * Bitmap of textures that need srgb to linear conversion.  If
+    * (srgb_to_linear & (1 << texture_index)) then the rgb (xyz)
+    * components of the texture are lowered to linear.
+    */
+   unsigned lower_srgb;
 } 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 7740e58..6bae3b7 100644
--- a/src/compiler/nir/nir_lower_tex.c
+++ b/src/compiler/nir/nir_lower_tex.c
@@ -275,6 +275,45 @@ swizzle_result(nir_builder *b, nir_tex_instr *tex, const uint8_t swizzle[4])
                                   swizzled->parent_instr);
 }
 
+static void
+linearize_srgb_result(nir_builder *b, nir_tex_instr *tex)
+{
+   assert(tex->dest.is_ssa);
+   assert(nir_tex_instr_dest_size(tex) == 4);
+   assert(nir_alu_type_get_base_type(tex->dest_type) == nir_type_float);
+
+   b->cursor = nir_after_instr(&tex->instr);
+
+   nir_ssa_def *components[4];
+
+   /* first three channels are rgb: */
+   for (unsigned i = 0; i < 3; i++) {
+      /* Formula is:
+       *    (comp <= 0.04045) ?
+       *          (comp / 12.92) :
+       *          pow((comp + 0.055) / 1.055, 2.4)
+       */
+      nir_ssa_def *comp = nir_channel(b, &tex->dest.ssa, i);
+      nir_ssa_def *low  = nir_fmul(b, comp, nir_imm_float(b, 1.0 / 12.92));
+      nir_ssa_def *high = nir_fpow(b,
+                                   nir_fmul(b,
+                                            nir_fadd(b,
+                                                     comp,
+                                                     nir_imm_float(b, 0.055)),
+                                            nir_imm_float(b, 1.0 / 1.055)),
+                                   nir_imm_float(b, 2.4));
+      nir_ssa_def *cond = nir_fge(b, nir_imm_float(b, 0.04045), comp);
+      components[i] = nir_bcsel(b, cond, low, high);
+   }
+
+   /* alpha is untouched: */
+   components[3] = nir_channel(b, &tex->dest.ssa, 3);
+
+   nir_ssa_def *linearized = nir_vec(b, components, 4);
+   nir_ssa_def_rewrite_uses_after(&tex->dest.ssa, nir_src_for_ssa(linearized),
+                                  linearized->parent_instr);
+}
+
 static bool
 nir_lower_tex_block(nir_block *block, void *void_state)
 {
@@ -323,6 +362,13 @@ nir_lower_tex_block(nir_block *block, void *void_state)
          swizzle_result(b, tex, options->swizzles[tex->texture_index]);
          state->progress = true;
       }
+
+      /* should be after swizzle so we know which channels are rgb: */
+      if (((1 << tex->texture_index) & options->lower_srgb) &&
+          !nir_tex_instr_is_query(tex) && !tex->is_shadow) {
+         linearize_srgb_result(b, tex);
+         state->progress = true;
+      }
    }
 
    return true;
-- 
2.5.5