EEVEE: Update LUT GGX generation shader

This modifies the principled BSDF and the Glass BSDF which now
have better fit to multiscatter GGX.

Code to generate the LUT have been updated and can run at runtime.

The refraction LUT has been changed to have the critical angle always
centered around one pixel so that interpolation can be mitigated.

Offline LUT data will be updated in another commit

This simplify the BTDF retreival removing the manual clean cut at
low roughness. This maximize the precision of the LUT by scalling
the sides by the critical angle.
I also touched the ior > 1.0 approximation to be smoother.

Also incluse some cleanup of bsdf_sampling.glsl

1 files changed, 17 insertions, 4 deletions

diff --git a/source/blender/draw/engines/eevee/eevee_materials.c b/source/blender/draw/engines/eevee/eevee_materials.c
index 5f2821730f1..841da7fd076 100644
--- a/source/blender/draw/engines/eevee/eevee_materials.c
+++ b/source/blender/draw/engines/eevee/eevee_materials.c
@@ -142,11 +142,20 @@ static void eevee_init_noise_texture(void)
   e_data.noise_tex = DRW_texture_create_2d(64, 64, GPU_RGBA16F, 0, (float *)blue_noise);
 }
 
+#define RUNTIME_LUT_CREATION 1
+
 static void eevee_init_util_texture(void)
 {
   const int layers = 4 + 16;
   float(*texels)[4] = MEM_mallocN(sizeof(float[4]) * 64 * 64 * layers, "utils texels");
   float(*texels_layer)[4] = texels;
+#if RUNTIME_LUT_CREATION
+  float *bsdf_ggx_lut = EEVEE_lut_update_ggx_brdf(64);
+  float(*btdf_ggx_lut)[64 * 64 * 2] = (float(*)[64 * 64 * 2]) EEVEE_lut_update_ggx_btdf(64, 16);
+#else
+  const float *bsdf_ggx_lut = bsdf_split_sum_ggx;
+  const float(*btdf_ggx_lut)[64 * 64 * 2] = btdf_split_sum_ggx;
+#endif
 
   /* Copy ltc_mat_ggx into 1st layer */
   memcpy(texels_layer, ltc_mat_ggx, sizeof(float[4]) * 64 * 64);
@@ -155,8 +164,8 @@ static void eevee_init_util_texture(void)
   /* Copy bsdf_split_sum_ggx into 2nd layer red and green channels.
    * Copy ltc_mag_ggx into 2nd layer blue and alpha channel. */
   for (int i = 0; i < 64 * 64; i++) {
-    texels_layer[i][0] = bsdf_split_sum_ggx[i * 2 + 0];
-    texels_layer[i][1] = bsdf_split_sum_ggx[i * 2 + 1];
+    texels_layer[i][0] = bsdf_ggx_lut[i * 2 + 0];
+    texels_layer[i][1] = bsdf_ggx_lut[i * 2 + 1];
     texels_layer[i][2] = ltc_mag_ggx[i * 2 + 0];
     texels_layer[i][3] = ltc_mag_ggx[i * 2 + 1];
   }
@@ -183,8 +192,8 @@ static void eevee_init_util_texture(void)
   /* Copy Refraction GGX LUT in layer 5 - 21 */
   for (int j = 0; j < 16; j++) {
     for (int i = 0; i < 64 * 64; i++) {
-      texels_layer[i][0] = btdf_split_sum_ggx[j * 2][i];
-      texels_layer[i][1] = 0.0; /* UNUSED */
+      texels_layer[i][0] = btdf_ggx_lut[j][i * 2 + 0];
+      texels_layer[i][1] = btdf_ggx_lut[j][i * 2 + 1];
       texels_layer[i][2] = 0.0; /* UNUSED */
       texels_layer[i][3] = 0.0; /* UNUSED */
     }
@@ -195,6 +204,10 @@ static void eevee_init_util_texture(void)
       64, 64, layers, GPU_RGBA16F, DRW_TEX_FILTER | DRW_TEX_WRAP, (float *)texels);
 
   MEM_freeN(texels);
+#if RUNTIME_LUT_CREATION
+  MEM_freeN(bsdf_ggx_lut);
+  MEM_freeN(btdf_ggx_lut);
+#endif
 }
 
 void EEVEE_update_noise(EEVEE_PassList *psl, EEVEE_FramebufferList *fbl, const double offsets[3])