Added presentations from EVI 2017

EVI - 2017/EVI 21/EVIray/tracer.cpp

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+#include "tracer.hpp"
+
+using glm::dot;
+using glm::normalize;
+using glm::refract;
+
+const float BIAS = 0.000001f;
+
+const vec3 BCKG_COLOR = vec3(0.1f);
+
+float Tracer::fresnel(const vec3 & i, const vec3 & n, const float ir1, const float ir2) const {
+  float cos_t1 = dot(i, n);
+  float cos_t2 = dot(normalize(refract(i, n, ir1 / ir2)), n);
+  float cos_t2s = (cos_t2 * cos_t2);
+  float omcos_t2s = 1.0f - cos_t2s;
+  omcos_t2s = omcos_t2s < 0.0f ? 0.0f : omcos_t2s;
+  float sin_t2 = (ir1 / ir2) * glm::sqrt(omcos_t2s);
+
+  if (sin_t2 >= 1.0f)
+    return 1.0f;
+
+  float fr_par = ((ir2 * cos_t1) - (ir1 * cos_t2)) / ((ir2 * cos_t1) + (ir1 * cos_t2));
+  float fr_per = ((ir1 * cos_t2) - (ir2 * cos_t1)) / ((ir1 * cos_t2) + (ir2 * cos_t1));
+
+  return ((fr_par * fr_par) + (fr_per * fr_per)) / 2.0f;
+}