star-sp

commit d011c481c4d08e9a7324cd75f4714344fef599ef
parent 69921a28f54332b506b651a1c39f8fec5dcdf763
Author: Christophe Coustet <christophe.coustet@meso-star.com>
Date:   Tue, 12 Apr 2016 18:31:32 +0200

Added Henyey-Greenstein distribution - not tested yet.

Used Richard's code.

Diffstat:
M
src/ssp.h
 | 
77
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

1 file changed, 77 insertions(+), 0 deletions(-)
diff --git a/src/ssp.h b/src/ssp.h
@@ -500,6 +500,83 @@ ssp_ran_hemisphere_cos_pdf(const float up[3], const float sample[3])
   return dot < 0.f ? 0.f : (float)(dot/PI);
 }
 
+/*******************************************************************************
+ * Henyey Greenstein distribution
+ ******************************************************************************/
+
+/* Return the probability distribution for a Henyey-Greenstein random
+ * variate with an implicit incident direction in Z */
+static INLINE float
+ssp_ran_sphere_hg_local_pdf(const double g, const float sample[3])
+{
+  double epsilon_g, epsilon_mu;
+  ASSERT(sample && f3_is_normalized(sample));
+  if (g>0) {
+    epsilon_g = 1-g;
+    epsilon_mu = 1-sample[2];
+  } else {
+    epsilon_g = 1+g;
+    epsilon_mu = 1+sample[2];
+  }
+  return (float)(1/(4*PI)
+		 *epsilon_g*(2-epsilon_g)
+		 *pow(epsilon_g*epsilon_g+2*epsilon_mu*(1-epsilon_g),-1.5));
+}
+
+/* Henyey-Greenstein sampling of an unit sphere for an incident direction 
+ * that is implicitly the Z axis. 
+ * The PDF of the generated sample is stored in sample[3] */
+static INLINE float*
+ssp_ran_sphere_hg_local(struct ssp_rng* rng, const double g, float sample[4])
+{
+  double phi, R, cos_theta, sin_theta;
+  ASSERT(rng && sample);
+  phi = 2 * PI * ssp_rng_canonical(rng);
+  R = ssp_rng_canonical(rng);
+  cos_theta = 2*R*(1+g)*(1+g)*(g*(R-1)+1)
+    /((1-g*(1-2*R))*(1-g*(1-2*R)))-1;
+  sin_theta = cos2sin(cos_theta);
+  sample[0] = (float)(cos(phi) * sin_theta);
+  sample[1] = (float)(sin(phi) * sin_theta);
+  sample[2] = (float)cos_theta;
+  sample[3] = ssp_ran_sphere_hg_local_pdf(g,sample);
+  return sample;
+}
+
+/* Return the probability distribution for a Henyey-Greenstein random
+ * variate with an explicit incident direction that is `up' */
+static INLINE float
+ssp_ran_sphere_hg_pdf(const float up[3], const double g, const float sample[3])
+{
+  double epsilon_g, epsilon_mu;
+  ASSERT(up && sample && f3_is_normalized(up) && f3_is_normalized(sample));
+  if (g>0) {
+    epsilon_g = 1-g;
+    epsilon_mu = 1-f3_dot(sample,up);
+  } else {
+    epsilon_g = 1+g;
+    epsilon_mu = 1+f3_dot(sample,up);
+  }
+  return (float)(1/(4*PI)
+		 *epsilon_g*(2-epsilon_g)
+		 *pow(epsilon_g*epsilon_g+2*epsilon_mu*(1-epsilon_g),-1.5));
+}
+
+/* Henyey-Greenstein sampling of an unit sphere for an incident direction
+ * that is `up'. 
+ * The PDF of the generated sample is stored in sample[3] */
+static INLINE float*
+ssp_ran_sphere_hg
+  (struct ssp_rng* rng, const float up[3], const double g, float sample[4])
+{
+  float sample_local[4];
+  float basis[9];
+  ASSERT(rng && up && sample && f3_is_normalized(up));
+  ssp_ran_sphere_hg_local(rng, g, sample_local);
+  sample[3]=sample_local[3];
+  return f33_mulf3(sample, f33_basis(basis, up), sample_local);
+}
+
 END_DECLS
 
 #endif /* SSP_H */