EEVEE: Fix most regression with ambient occlusion

Occlusion had change because of the way it was applied.
Get back to almost the same thing we had previously. The only thing
that changed is the occlusion of Normal mapped surface.

It is a bit less noticeable due to a new approximation we make.

3 files changed, 32 insertions, 12 deletions

diff --git a/source/blender/draw/engines/eevee/shaders/ambient_occlusion_lib.glsl b/source/blender/draw/engines/eevee/shaders/ambient_occlusion_lib.glsl
index d250c9c9cce..7c0ae3881d7 100644
--- a/source/blender/draw/engines/eevee/shaders/ambient_occlusion_lib.glsl
+++ b/source/blender/draw/engines/eevee/shaders/ambient_occlusion_lib.glsl
@@ -191,15 +191,15 @@ void gtao_deferred(
   dirs.xy = get_ao_dir(noise.x * 0.5);
   dirs.zw = get_ao_dir(noise.x * 0.5 + 0.5);
 
-  bent_normal = normal * 1e-8;
-  visibility = 1e-8;
+  bent_normal = vec3(0.0);
+  visibility = 0.0;
 
   horizons = unpack_horizons(horizons);
 
   integrate_slice(normal, dirs.xy, horizons.xy, visibility, bent_normal);
   integrate_slice(normal, dirs.zw, horizons.zw, visibility, bent_normal);
 
-  bent_normal = normalize(bent_normal / visibility);
+  bent_normal = safe_normalize(bent_normal);
 
   visibility *= 0.5; /* We integrated 2 slices. */
 }
@@ -240,6 +240,17 @@ float gtao_multibounce(float visibility, vec3 albedo)
   return max(x, ((x * a + b) * x + c) * x);
 }
 
+float diffuse_occlusion(vec3 N, vec3 vis_cone_dir, float vis_cone_aperture_cos, vec3 albedo)
+{
+  if ((int(aoSettings) & USE_AO) == 0) {
+    return 1.0;
+  }
+  /* If the shading normal is orthogonal to the geometric normal, it should be half lit. */
+  float horizon_fac = saturate(dot(N, vis_cone_dir) * 0.5 + 0.5);
+  float ao = vis_cone_aperture_cos * horizon_fac;
+  return gtao_multibounce(ao, albedo);
+}
+
 float specular_occlusion(float NV, float AO, float roughness)
 {
   return saturate(pow(NV + AO, roughness) - 1.0 + AO);
@@ -263,10 +274,6 @@ float occlusion_compute(vec3 N, vec3 vpos, vec4 rand, out vec3 bent_normal)
     visibility = max(1e-3, visibility);
 
     if ((int(aoSettings) & USE_BENT_NORMAL) != 0) {
-      /* The bent normal will show the facet look of the mesh. Try to minimize this. */
-      float mix_fac = visibility * visibility * visibility;
-      bent_normal = normalize(mix(bent_normal, vnor, mix_fac));
-
       bent_normal = transform_direction(ViewMatrixInverse, bent_normal);
     }
     else {
diff --git a/source/blender/draw/engines/eevee/shaders/bsdf_common_lib.glsl b/source/blender/draw/engines/eevee/shaders/bsdf_common_lib.glsl
index 25eb0133616..f050cf3a08a 100644
--- a/source/blender/draw/engines/eevee/shaders/bsdf_common_lib.glsl
+++ b/source/blender/draw/engines/eevee/shaders/bsdf_common_lib.glsl
@@ -1,6 +1,15 @@
 
 #pragma BLENDER_REQUIRE(common_math_lib.glsl)
 
+vec3 diffuse_dominant_dir(vec3 N, vec3 vis_cone_dir, float vis_cone_aperture_cos)
+{
+  /* TODO(fclem) revisit this. bent too much towards vis_cone_dir. */
+  vis_cone_aperture_cos *= sqr(vis_cone_aperture_cos);
+
+  N = mix(vis_cone_dir, N, vis_cone_aperture_cos);
+  return normalize(N);
+}
+
 vec3 specular_dominant_dir(vec3 N, vec3 V, float roughness)
 {
   vec3 R = -reflect(V, N);
diff --git a/source/blender/draw/engines/eevee/shaders/closure_eval_diffuse_lib.glsl b/source/blender/draw/engines/eevee/shaders/closure_eval_diffuse_lib.glsl
index 28aaa6afd44..1e65d3ccb87 100644
--- a/source/blender/draw/engines/eevee/shaders/closure_eval_diffuse_lib.glsl
+++ b/source/blender/draw/engines/eevee/shaders/closure_eval_diffuse_lib.glsl
@@ -10,7 +10,8 @@ struct ClosureInputDiffuse {
 #define CLOSURE_INPUT_Diffuse_DEFAULT ClosureInputDiffuse(vec3(0.0), vec3(0.0))
 
 struct ClosureEvalDiffuse {
-  float dummy;
+  vec3 probe_sampling_dir; /** Direction to sample probes from. */
+  float ambient_occlusion; /** Final occlusion for distant lighting. */
 };
 
 /* Stubs. */
@@ -26,7 +27,10 @@ ClosureEvalDiffuse closure_Diffuse_eval_init(inout ClosureInputDiffuse cl_in,
   cl_out.radiance = vec3(0.0);
 
   ClosureEvalDiffuse cl_eval;
-  cl_eval.dummy = 0.0;
+  cl_eval.ambient_occlusion = diffuse_occlusion(
+      cl_in.N, cl_common.bent_normal, cl_common.occlusion, cl_in.albedo);
+  cl_eval.probe_sampling_dir = diffuse_dominant_dir(
+      cl_in.N, cl_common.bent_normal, cl_common.occlusion);
   return cl_eval;
 }
 
@@ -49,7 +53,7 @@ void closure_Diffuse_grid_eval(ClosureInputDiffuse cl_in,
                                inout ClosureOutputDiffuse cl_out)
 {
   vec3 probe_radiance = probe_evaluate_grid(
-      grid.data, cl_common.P, cl_common.bent_normal, grid.local_pos);
+      grid.data, cl_common.P, cl_eval.probe_sampling_dir, grid.local_pos);
   cl_out.radiance += grid.attenuation * probe_radiance;
 }
 
@@ -61,11 +65,11 @@ void closure_Diffuse_indirect_end(ClosureInputDiffuse cl_in,
   /* If not enough light has been accumulated from probes, use the world specular cubemap
    * to fill the remaining energy needed. */
   if (cl_common.diffuse_accum > 0.0) {
-    vec3 probe_radiance = probe_evaluate_world_diff(cl_common.bent_normal);
+    vec3 probe_radiance = probe_evaluate_world_diff(cl_eval.probe_sampling_dir);
     cl_out.radiance += cl_common.diffuse_accum * probe_radiance;
   }
   /* Apply occlusion on radiance before the light loop. */
-  cl_out.radiance *= gtao_multibounce(cl_common.occlusion, cl_in.albedo);
+  cl_out.radiance *= cl_eval.ambient_occlusion;
 }
 
 void closure_Diffuse_eval_end(ClosureInputDiffuse cl_in,