star-sf

commit 408e9bc133b2de5581f1bc37a28414e84f69c8ed
parent c434ba7c1e31b931360e64772f952dde6a283652
Author: Vincent Forest <vincent.forest@meso-star.com>
Date:   Sat, 10 Sep 2016 14:34:31 +0200

Implement the Fresnel term of the dielectric/conductor interfaces

Diffstat:
M
cmake/CMakeLists.txt
 | 
1
+
A
src/ssf_fresnel_dielectric_conductor.c
 | 
113
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

2 files changed, 114 insertions(+), 0 deletions(-)
diff --git a/cmake/CMakeLists.txt b/cmake/CMakeLists.txt
@@ -52,6 +52,7 @@ set(SSF_FILES_SRC
   ssf_bsdf.c
   ssf_bxdf.c
   ssf_fresnel.c
+  ssf_fresnel_dielectric_conductor.c
   ssf_fresnel_dielectric_dielectric.c
   ssf_fresnel_no_op.c
   ssf_specular_reflection.c)
diff --git a/src/ssf_fresnel_dielectric_conductor.c b/src/ssf_fresnel_dielectric_conductor.c
@@ -0,0 +1,113 @@
+/* Copyright (C) |Meso|Star> 2016 (contact@meso-star.com)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>. */
+
+#include "ssf.h"
+#include "ssf_fresnel_c.h"
+
+#include <math.h>
+
+struct fresnel_dielectric_conductor {
+  double eta_i; /* Refraction id of the dielectric medium */
+  double eta_t; /* Real part of the refraction index */
+  double eta_k_t; /* Imaginary part of the refraction index */
+};
+
+/*******************************************************************************
+ * Private functions
+ ******************************************************************************/
+static res_T
+fresnel_dielectric_conductor_init
+  (struct mem_allocator* allocator, void* fresnel)
+{
+  struct fresnel_dielectric_conductor* fc = fresnel;
+  (void)allocator;
+  ASSERT(fresnel);
+  fc->eta_i = 0.0;
+  fc->eta_t = 0.0;
+  fc->eta_k_t = 0.0;
+  return RES_OK;
+}
+
+static void
+fresnel_dielectric_conductor_release(void* fresnel)
+{
+  (void)fresnel;
+}
+
+/* Code from
+ * https://seblagarde.wordpress.com/2013/04/29/memo-on-fresnel-equations/ */
+static double
+fresnel_dielectric_conductor_eval(void* fresnel, const double cos_theta_i)
+{
+  const struct fresnel_dielectric_conductor* fc = fresnel;
+  double cos_theta_i2;
+  double sin_theta_i2;
+  double eta, eta_k, eta2, eta_k2;
+  double t0, t1, t2, t3, t4;
+  double a;
+  double a2_add_b2;
+  double Rp, Rs;
+  ASSERT(fresnel && cos_theta_i >= 0);
+
+  cos_theta_i2 = cos_theta_i * cos_theta_i;
+  sin_theta_i2 = 1.0 - cos_theta_i2;
+  eta = fc->eta_t / fc->eta_i; /* Real part */
+  eta_k = fc->eta_k_t / fc->eta_i; /* Imaginary part */
+  eta2 = eta*eta;
+  eta_k2 = eta_k*eta_k;
+
+  t0 = eta2 - eta_k2 - sin_theta_i2;
+  a2_add_b2 = sqrt(t0*t0 + 4*eta2*eta_k2);
+  t1 = a2_add_b2 + cos_theta_i2;
+  a = sqrt(0.5 * (a2_add_b2 + t0));
+  t2 = 2.0*a*cos_theta_i;
+  Rs = (t1 - t2) / (t1 + t2);
+
+  t3 = cos_theta_i2 * a2_add_b2 + sin_theta_i2 * sin_theta_i2;
+  t4 = t2 * sin_theta_i2;
+  Rp = Rs * (t3 - t4) / (t3 + t4);
+  return 0.5 * (Rp + Rs);
+}
+
+/*******************************************************************************
+ * Exported symbols
+ ******************************************************************************/
+const struct ssf_fresnel_type ssf_fresnel_dielectric_conductor = {
+  fresnel_dielectric_conductor_init,
+  fresnel_dielectric_conductor_release,
+  fresnel_dielectric_conductor_eval,
+  sizeof(struct fresnel_dielectric_conductor),
+  ALIGNOF(struct fresnel_dielectric_conductor)
+};
+
+res_T
+ssf_fresnel_dielectric_conductor_setup
+  (struct ssf_fresnel* fresnel,
+   const double eta_i,
+   const double eta_t,
+   const double eta_k_t)
+{
+  struct fresnel_dielectric_conductor* fc;
+  if(!fresnel 
+  || !FRESNEL_TYPE_EQ(&fresnel->type, &ssf_fresnel_dielectric_conductor)) {
+    return RES_BAD_ARG;
+  }
+  fc = fresnel->data;
+  fc->eta_i = eta_i;
+  fc->eta_t = eta_t;
+  fc->eta_k_t = eta_k_t;
+  return RES_OK;
+}
+