star-sf

commit 12122fa4af59f17cd039be2ce4e68d86bb3e0ea4
parent 74d2016369d88d761fb28270b05921c6d08109fa
Author: Vincent Forest <vincent.forest@meso-star.com>
Date:   Fri, 30 Sep 2016 16:35:24 +0200

Add the Microfacet2 BRDF

Ensure the energy conservation property without requiring the
normalization of the BRDF.

Diffstat:
M
src/ssf.h
 | 
6
++++++
M
src/ssf_microfacet_reflection.c
 | 
87
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
M
src/test_ssf_microfacet_reflection.c
 | 
8
+-------

3 files changed, 92 insertions(+), 9 deletions(-)
diff --git a/src/ssf.h b/src/ssf.h
@@ -163,6 +163,12 @@ SSF_API const struct ssf_bxdf_type ssf_specular_reflection;
 SSF_API const struct ssf_bxdf_type ssf_lambertian_reflection;
 /* Glossy reflections with respect to a microfacet distribution */
 SSF_API const struct ssf_bxdf_type ssf_microfacet_reflection;
+/* Glossy reflections with respect to a microfacet distribution. In contrast to
+ * the common microfacet model, this BRDF ensures, by construction, the energy
+ * conservation property without requiring the normalization of the BRDF.  As a
+ * conterpart, it only provides the sample function. The others functions
+ * return invalid results */
+SSF_API const struct ssf_bxdf_type ssf_microfacet2_reflection;
 
 /* Fresnel term for perfect reflection */
 SSF_API const struct ssf_fresnel_type ssf_fresnel_no_op;
diff --git a/src/ssf_microfacet_reflection.c b/src/ssf_microfacet_reflection.c
@@ -25,7 +25,7 @@ struct microfacet_reflection {
 };
 
 /*******************************************************************************
- * Private functions
+ * Microfacet functions
  ******************************************************************************/
 static res_T
 microfacet_reflection_init(struct mem_allocator* allocator, void* data)
@@ -94,7 +94,7 @@ microfacet_reflection_sample
   double R;
   ASSERT(data && u>=0 && u<1 && v>=0 && v<1 && wo && N && wi);
   ASSERT(d3_is_normalized(wo) && d3_is_normalized(N));
-  ASSERT(bxdf->distrib);
+  ASSERT(bxdf->distrib && bxdf->fresnel);
 
   if(d3_dot(wo, N) <= 0.0) return 0.0;
 
@@ -130,6 +130,78 @@ microfacet_reflection_rho(void* data, const double wo[3], const double N[3])
 }
 
 /*******************************************************************************
+ * Microfacet 2 functions
+ ******************************************************************************/
+static FINLINE double
+microfacet2_reflection_sample
+  (void* data,
+   const double u,
+   const double v,
+   const double wo[3],
+   const double N[3],
+   double wi[3],
+   double* pdf)
+{
+  struct microfacet_reflection* bxdf = data;
+  double dir[3];
+  double wh[3];
+  double p;
+  double troughput = 1;
+  ASSERT(data && u>=0 && u<1 && v>=0 && v<1 && wo && N && wi);
+  ASSERT(d3_is_normalized(wo) && d3_is_normalized(N));
+  ASSERT(bxdf->distrib);
+
+  if(d3_dot(wo, N) <= 0.0) return 0.0;
+
+  do { /* Sample a micro facet that front faces 'wo' */
+    ssf_microfacet_distribution_sample(bxdf->distrib, u, v, wo, N, wh, &p);
+  } while(d3_dot(wo, wh) <= 0);
+
+  reflect(dir, wo, wh);
+  for(;;) {
+    troughput *= ssf_fresnel_eval(bxdf->fresnel, d3_dot(wh, dir));
+
+    /* Do not take care of inter-reflections for sampled directions that point
+     * outward the macro surface, i.e. simply stop the "random walk". */
+    if(d3_dot(dir, N) > 0) break;
+
+    /* Handle directions that point toward the macro surface has
+     * inter-reflections */
+    do { /* Sample a microfacet that front faces 'wi' */
+      ssf_microfacet_distribution_sample(bxdf->distrib, u, v, dir, N, wh, &p);
+    } while(d3_dot(dir, wh) <= 0);
+    reflect(dir, dir, wh);
+  }
+
+  *pdf = NaN;
+  d3_set(wi, dir);
+  return troughput;
+}
+
+static FINLINE double
+microfacet2_reflection_eval
+  (void* data, const double wo[3], const double N[3], const double wi[3])
+{
+  (void)data, (void)wo, (void)N, (void)wi;
+  return NaN;
+}
+
+static FINLINE double
+microfacet2_reflection_pdf
+  (void* data, const double wo[3], const double N[3], const double wi[3])
+{
+  (void)data, (void)wo, (void)N, (void)wi;
+  return NaN;
+}
+
+static FINLINE double
+microfacet2_reflection_rho(void* data, const double wo[3], const double N[3])
+{
+  (void)data, (void)wo, (void)N;
+  return NaN;
+}
+
+/*******************************************************************************
  * Exported symbols
  ******************************************************************************/
 const struct ssf_bxdf_type ssf_microfacet_reflection = {
@@ -143,6 +215,17 @@ const struct ssf_bxdf_type ssf_microfacet_reflection = {
   ALIGNOF(struct microfacet_reflection)
 };
 
+const struct ssf_bxdf_type ssf_microfacet2_reflection = {
+  microfacet_reflection_init,
+  microfacet_reflection_release,
+  microfacet2_reflection_sample,
+  microfacet2_reflection_eval,
+  microfacet2_reflection_pdf,
+  microfacet2_reflection_rho,
+  sizeof(struct microfacet_reflection),
+  ALIGNOF(struct microfacet_reflection)
+};
+
 res_T
 ssf_microfacet_reflection_setup
   (struct ssf_bxdf* bxdf,
diff --git a/src/test_ssf_microfacet_reflection.c b/src/test_ssf_microfacet_reflection.c
@@ -21,18 +21,11 @@
 int
 main(int argc, char** argv)
 {
-  const size_t NSTEPS = 100000;
   struct mem_allocator allocator;
   struct ssf_bxdf* bxdf;
   struct ssf_bxdf* dummy;
   struct ssf_fresnel* F;
   struct ssf_microfacet_distribution* D;
-  double wo[3], wi[3];
-  double N[3];
-  double pdf;
-  double sum, sum_sqr;
-  double E, V, SE;
-  size_t i;
   (void)argc, (void)argv;
 
   mem_init_proxy_allocator(&allocator, &mem_default_allocator);
@@ -54,6 +47,7 @@ main(int argc, char** argv)
   CHECK(ssf_microfacet_reflection_setup(bxdf, F, D), RES_OK);
 
   /* Numerically evaluate rho */
+  /* TODO */
 #if 0
   d3(N, 0, 1, 0);
   sum = sum_sqr = 0;