1 files changed, 61 insertions, 13 deletions

diff --git a/source/blender/draw/engines/eevee/shaders/bsdf_sampling_lib.glsl b/source/blender/draw/engines/eevee/shaders/bsdf_sampling_lib.glsl
index bbc79a2d05b..004d884dc75 100644
--- a/source/blender/draw/engines/eevee/shaders/bsdf_sampling_lib.glsl
+++ b/source/blender/draw/engines/eevee/shaders/bsdf_sampling_lib.glsl
@@ -1,4 +1,5 @@
 
+#pragma BLENDER_REQUIRE(common_math_geom_lib.glsl)
 #pragma BLENDER_REQUIRE(bsdf_common_lib.glsl)
 
 uniform sampler1D texHammersley;
@@ -8,6 +9,11 @@ vec3 tangent_to_world(vec3 vector, vec3 N, vec3 T, vec3 B)
   return T * vector.x + B * vector.y + N * vector.z;
 }
 
+vec3 world_to_tangent(vec3 vector, vec3 N, vec3 T, vec3 B)
+{
+  return vec3(dot(T, vector), dot(B, vector), dot(N, vector));
+}
+
 #ifdef HAMMERSLEY_SIZE
 vec3 hammersley_3d(float i, float invsamplenbr)
 {
@@ -22,9 +28,18 @@ vec3 hammersley_3d(float i, float invsamplenbr)
 
 /* -------------- BSDFS -------------- */
 
-float pdf_ggx_reflect(float NH, float a2)
+#define USE_VISIBLE_NORMAL 1
+
+float pdf_ggx_reflect(float NH, float NV, float VH, float alpha)
 {
+  float a2 = sqr(alpha);
+#if USE_VISIBLE_NORMAL
+  float D = a2 / D_ggx_opti(NH, a2);
+  float G1 = NV * 2.0 / G1_Smith_GGX_opti(NV, a2);
+  return G1 * VH * D / NV;
+#else
   return NH * a2 / D_ggx_opti(NH, a2);
+#endif
 }
 
 float pdf_hemisphere()
@@ -32,22 +47,50 @@ float pdf_hemisphere()
   return 0.5 * M_1_PI;
 }
 
-vec3 sample_ggx(vec3 rand, float a2)
+vec3 sample_ggx(vec3 rand, float alpha, vec3 Vt)
 {
+#if USE_VISIBLE_NORMAL
+  /* From:
+   * "A Simpler and Exact Sampling Routine for the GGXDistribution of Visible Normals"
+   * by Eric Heitz.
+   * http://jcgt.org/published/0007/04/01/slides.pdf
+   * View vector is expected to be in tangent space. */
+
+  /* Stretch view. */
+  vec3 Th, Bh, Vh = normalize(vec3(alpha * Vt.xy, Vt.z));
+  make_orthonormal_basis(Vh, Th, Bh);
+  /* Sample point with polar coordinates (r, phi). */
+  float r = sqrt(rand.x);
+  float x = r * rand.y;
+  float y = r * rand.z;
+  float s = 0.5 * (1.0 + Vh.z);
+  y = (1.0 - s) * sqrt(1.0 - x * x) + s * y;
+  float z = sqrt(saturate(1.0 - x * x - y * y));
+  /* Compute normal. */
+  vec3 Hh = x * Th + y * Bh + z * Vh;
+  /* Unstretch. */
+  vec3 Ht = normalize(vec3(alpha * Hh.xy, saturate(Hh.z)));
+  /* Microfacet Normal. */
+  return Ht;
+#else
   /* Theta is the cone angle. */
-  float z = sqrt((1.0 - rand.x) / (1.0 + a2 * rand.x - rand.x)); /* cos theta */
-  float r = sqrt(max(0.0, 1.0 - z * z));                         /* sin theta */
+  float z = sqrt((1.0 - rand.x) / (1.0 + sqr(alpha) * rand.x - rand.x)); /* cos theta */
+  float r = sqrt(max(0.0, 1.0 - z * z));                                 /* sin theta */
   float x = r * rand.y;
   float y = r * rand.z;
-
   /* Microfacet Normal */
   return vec3(x, y, z);
+#endif
 }
 
-vec3 sample_ggx(vec3 rand, float a2, vec3 N, vec3 T, vec3 B, out float NH)
+vec3 sample_ggx(vec3 rand, float alpha, vec3 V, vec3 N, vec3 T, vec3 B, out float pdf)
 {
-  vec3 Ht = sample_ggx(rand, a2);
-  NH = Ht.z;
+  vec3 Vt = world_to_tangent(V, N, T, B);
+  vec3 Ht = sample_ggx(rand, alpha, Vt);
+  float NH = saturate(Ht.z);
+  float NV = saturate(Vt.z);
+  float VH = saturate(dot(Vt, Ht));
+  pdf = pdf_ggx_reflect(NH, NV, VH, alpha);
   return tangent_to_world(Ht, N, T, B);
 }
 
@@ -69,18 +112,23 @@ vec3 sample_hemisphere(vec3 rand, vec3 N, vec3 T, vec3 B)
 }
 
 #ifdef HAMMERSLEY_SIZE
-vec3 sample_ggx(float nsample, float inv_sample_count, float a2, vec3 N, vec3 T, vec3 B)
+vec3 sample_ggx(float nsample,
+                float inv_sample_count,
+                float alpha,
+                vec3 V,
+                vec3 N,
+                vec3 T,
+                vec3 B,
+                out float pdf)
 {
   vec3 Xi = hammersley_3d(nsample, inv_sample_count);
-  vec3 Ht = sample_ggx(Xi, a2);
-  return tangent_to_world(Ht, N, T, B);
+  return sample_ggx(Xi, alpha, V, N, T, B, pdf);
 }
 
 vec3 sample_hemisphere(float nsample, float inv_sample_count, vec3 N, vec3 T, vec3 B)
 {
   vec3 Xi = hammersley_3d(nsample, inv_sample_count);
-  vec3 Ht = sample_hemisphere(Xi);
-  return tangent_to_world(Ht, N, T, B);
+  return sample_hemisphere(Xi, N, T, B);
 }
 
 vec3 sample_cone(float nsample, float inv_sample_count, float angle, vec3 N, vec3 T, vec3 B)