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, 70 insertions, 118 deletions

diff --git a/source/blender/draw/engines/eevee/eevee_lut_gen.c b/source/blender/draw/engines/eevee/eevee_lut_gen.c
index 18645fea5e0..770134d27f9 100644
--- a/source/blender/draw/engines/eevee/eevee_lut_gen.c
+++ b/source/blender/draw/engines/eevee/eevee_lut_gen.c
@@ -27,145 +27,97 @@
 
 #include "DRW_render.h"
 
-#include "BLI_alloca.h"
+#include "BLI_fileops.h"
 #include "BLI_rand.h"
 #include "BLI_string_utils.h"
 
 #include "eevee_private.h"
 
-static struct GPUTexture *create_ggx_lut_texture(int UNUSED(w), int UNUSED(h))
-{
-  struct GPUTexture *tex;
-  struct GPUFrameBuffer *fb = NULL;
-  static float samples_len = 8192.0f;
-  static float inv_samples_len = 1.0f / 8192.0f;
+#define DO_FILE_OUTPUT 0
 
-  DRWPass *pass = DRW_pass_create("LightProbe Filtering", DRW_STATE_WRITE_COLOR);
+float *EEVEE_lut_update_ggx_brdf(int lut_size)
+{
+  DRWPass *pass = DRW_pass_create(__func__, DRW_STATE_WRITE_COLOR);
   DRWShadingGroup *grp = DRW_shgroup_create(EEVEE_shaders_ggx_lut_sh_get(), pass);
-  DRW_shgroup_uniform_float(grp, "sampleCount", &samples_len, 1);
-  DRW_shgroup_uniform_float(grp, "invSampleCount", &inv_samples_len, 1);
-  DRW_shgroup_uniform_texture(grp, "texHammersley", e_data.hammersley);
-  DRW_shgroup_uniform_texture(grp, "texJitter", e_data.jitter);
-
-  struct GPUBatch *geom = DRW_cache_fullscreen_quad_get();
-  DRW_shgroup_call(grp, geom, NULL);
-
-  float *texels = MEM_mallocN(sizeof(float[2]) * w * h, "lut");
-
-  tex = DRW_texture_create_2d(w, h, GPU_RG16F, DRW_TEX_FILTER, (float *)texels);
-
-  DRWFboTexture tex_filter = {&tex, GPU_RG16F, DRW_TEX_FILTER};
-  GPU_framebuffer_init(&fb, &draw_engine_eevee_type, w, h, &tex_filter, 1);
-
+  DRW_shgroup_uniform_float_copy(grp, "sampleCount", 64.0f); /* Actual sample count is squared. */
+  DRW_shgroup_call_procedural_triangles(grp, NULL, 1);
+
+  GPUTexture *tex = DRW_texture_create_2d(lut_size, lut_size, GPU_RG16F, 0, NULL);
+  GPUFrameBuffer *fb = NULL;
+  GPU_framebuffer_ensure_config(&fb,
+                                {
+                                    GPU_ATTACHMENT_NONE,
+                                    GPU_ATTACHMENT_TEXTURE(tex),
+                                });
   GPU_framebuffer_bind(fb);
   DRW_draw_pass(pass);
-
-  float *data = MEM_mallocN(sizeof(float[3]) * w * h, "lut");
-  GPU_framebuffer_read_color(fb, 0, 0, w, h, 3, 0, GPU_DATA_FLOAT, data);
-
-  printf("{");
-  for (int i = 0; i < w * h * 3; i += 3) {
-    printf("%ff, %ff, ", data[i], data[i + 1]);
-    i += 3;
-    printf("%ff, %ff, ", data[i], data[i + 1]);
-    i += 3;
-    printf("%ff, %ff, ", data[i], data[i + 1]);
-    i += 3;
-    printf("%ff, %ff, \n", data[i], data[i + 1]);
+  GPU_FRAMEBUFFER_FREE_SAFE(fb);
+
+  float *data = GPU_texture_read(tex, GPU_DATA_FLOAT, 0);
+  GPU_texture_free(tex);
+#if DO_FILE_OUTPUT
+  /* Content is to be put inside eevee_lut.c */
+  FILE *f = BLI_fopen("bsdf_split_sum_ggx.h", "w");
+  fprintf(f, "const float bsdf_split_sum_ggx[%d * %d * 2] = {", lut_size, lut_size);
+  for (int i = 0; i < lut_size * lut_size * 2;) {
+    fprintf(f, "\n    ");
+    for (int j = 0; j < 4; j++, i += 2) {
+      fprintf(f, "%ff, %ff, ", data[i], data[i + 1]);
+    }
   }
-  printf("}");
-
-  MEM_freeN(texels);
-  MEM_freeN(data);
+  fprintf(f, "\n};\n");
+  fclose(f);
+#endif
 
-  return tex;
+  return data;
 }
 
-static struct GPUTexture *create_ggx_refraction_lut_texture(int w, int h)
+float *EEVEE_lut_update_ggx_btdf(int lut_size, int lut_depth)
 {
-  struct GPUTexture *tex;
-  struct GPUTexture *hammersley = create_hammersley_sample_texture(8192);
-  struct GPUFrameBuffer *fb = NULL;
-  static float samples_len = 8192.0f;
-  static float a2 = 0.0f;
-  static float inv_samples_len = 1.0f / 8192.0f;
-
-  DRWPass *pass = DRW_pass_create("LightProbe Filtering", DRW_STATE_WRITE_COLOR);
+  float roughness;
+  DRWPass *pass = DRW_pass_create(__func__, DRW_STATE_WRITE_COLOR);
   DRWShadingGroup *grp = DRW_shgroup_create(EEVEE_shaders_ggx_refraction_lut_sh_get(), pass);
-  DRW_shgroup_uniform_float(grp, "a2", &a2, 1);
-  DRW_shgroup_uniform_float(grp, "sampleCount", &samples_len, 1);
-  DRW_shgroup_uniform_float(grp, "invSampleCount", &inv_samples_len, 1);
-  DRW_shgroup_uniform_texture(grp, "texHammersley", hammersley);
-  DRW_shgroup_uniform_texture(grp, "utilTex", e_data.util_tex);
-
-  struct GPUBatch *geom = DRW_cache_fullscreen_quad_get();
-  DRW_shgroup_call(grp, geom, NULL);
-
-  float *texels = MEM_mallocN(sizeof(float[2]) * w * h, "lut");
-
-  tex = DRW_texture_create_2d(w, h, GPU_R16F, DRW_TEX_FILTER, (float *)texels);
-
-  DRWFboTexture tex_filter = {&tex, GPU_R16F, DRW_TEX_FILTER};
-  GPU_framebuffer_init(&fb, &draw_engine_eevee_type, w, h, &tex_filter, 1);
+  DRW_shgroup_uniform_float_copy(grp, "sampleCount", 64.0f); /* Actual sample count is squared. */
+  DRW_shgroup_uniform_float(grp, "z", &roughness, 1);
+  DRW_shgroup_call_procedural_triangles(grp, NULL, 1);
+
+  GPUTexture *tex = DRW_texture_create_2d_array(lut_size, lut_size, lut_depth, GPU_RG16F, 0, NULL);
+  GPUFrameBuffer *fb = NULL;
+  for (int i = 0; i < lut_depth; i++) {
+    GPU_framebuffer_ensure_config(&fb,
+                                  {
+                                      GPU_ATTACHMENT_NONE,
+                                      GPU_ATTACHMENT_TEXTURE_LAYER(tex, i),
+                                  });
+    GPU_framebuffer_bind(fb);
+    roughness = i / (lut_depth - 1.0f);
+    DRW_draw_pass(pass);
+  }
 
-  GPU_framebuffer_bind(fb);
+  GPU_FRAMEBUFFER_FREE_SAFE(fb);
 
-  float *data = MEM_mallocN(sizeof(float[3]) * w * h, "lut");
+  float *data = GPU_texture_read(tex, GPU_DATA_FLOAT, 0);
+  GPU_texture_free(tex);
 
-  float inc = 1.0f / 31.0f;
-  float roughness = 1e-8f - inc;
+#if DO_FILE_OUTPUT
+  /* Content is to be put inside eevee_lut.c. Don't forget to format the output. */
   FILE *f = BLI_fopen("btdf_split_sum_ggx.h", "w");
-  fprintf(f, "static float btdf_split_sum_ggx[32][64 * 64] = {\n");
-  do {
-    roughness += inc;
-    CLAMP(roughness, 1e-4f, 1.0f);
-    a2 = powf(roughness, 4.0f);
-    DRW_draw_pass(pass);
-
-    GPU_framebuffer_read_data(0, 0, w, h, 3, 0, data);
-
-#if 1
-    fprintf(f, "\t{\n\t\t");
-    for (int i = 0; i < w * h * 3; i += 3) {
-      fprintf(f, "%ff,", data[i]);
-      if (((i / 3) + 1) % 12 == 0) {
-        fprintf(f, "\n\t\t");
-      }
-      else {
-        fprintf(f, " ");
-      }
-    }
-    fprintf(f, "\n\t},\n");
-#else
-    for (int i = 0; i < w * h * 3; i += 3) {
-      if (data[i] < 0.01) {
-        printf(" ");
-      }
-      else if (data[i] < 0.3) {
-        printf(".");
-      }
-      else if (data[i] < 0.6) {
-        printf("+");
-      }
-      else if (data[i] < 0.9) {
-        printf("%%");
-      }
-      else {
-        printf("#");
-      }
-      if ((i / 3 + 1) % 64 == 0) {
-        printf("\n");
+  fprintf(f, "const float btdf_split_sum_ggx[%d][%d * %d * 2] = {", lut_depth, lut_size, lut_size);
+  fprintf(f, "\n    ");
+  int ofs = 0;
+  for (int d = 0; d < lut_depth; d++) {
+    fprintf(f, "{\n");
+    for (int i = 0; i < lut_size * lut_size * 2;) {
+      for (int j = 0; j < 4; j++, i += 2, ofs += 2) {
+        fprintf(f, "%ff, %ff, ", data[ofs], data[ofs + 1]);
       }
+      fprintf(f, "\n    ");
     }
-#endif
-
-  } while (roughness < 1.0f);
-  fprintf(f, "\n};\n");
-
+    fprintf(f, "},\n");
+  }
+  fprintf(f, "};\n");
   fclose(f);
+#endif
 
-  MEM_freeN(texels);
-  MEM_freeN(data);
-
-  return tex;
+  return data;
 }