From 52d11df35ca9846085b910e2e40434b48847d9d8 Mon Sep 17 00:00:00 2001
From: Keuin <keuinx@gmail.com>
Date: Sat, 16 Apr 2022 15:22:40 +0800
Subject: Add dielectric reflectiveness (using Schlick's Approximation).

---
 material_dielectric.cpp | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

(limited to 'material_dielectric.cpp')

diff --git a/material_dielectric.cpp b/material_dielectric.cpp
index 3aaf259..ed8e4eb 100644
--- a/material_dielectric.cpp
+++ b/material_dielectric.cpp
@@ -9,13 +9,24 @@ bool material_dielectric::scatter(ray3d &r, const object &hit_obj, double hit_t,
     assert(hit_obj.is_on(hit_p));
     auto n = hit_obj.normal_vector(hit_p);
     auto ri_ = ri_inv;
-    if (dot(r.direction(), n) > 0) {
+    auto cos1 = dot(r.direction(), n); // -cos(a1)
+    if (cos1 > 0) {
         // the ray is started from the object's inner,
         // use normal vector and ri on the surface's inner side
         n = -n;
         ri_ = 1.0 / ri_;
+    } else {
+        cos1 = -cos1;
+    }
+    vec3d r2;
+    // determine reflection or refraction using Schlick's Approximation.
+    if (reflectance(cos1, ri_) > ruvg.range01_scalar()) {
+        // reflect
+        r2 = n.reflect(r.direction());
+    } else {
+        // refract
+        r2 = n.refract<true>(r.direction(), ri_);
     }
-    const auto r2 = n.refract<true>(r.direction(), ri_); // refracted vector
     r.direction(r2.unit_vec());
     r.source(hit_p);
     return true;
-- 
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