From 1d7e01f424f127935e63aee91a2e2ca416157d0f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?arvid=20schr=C3=B6der?= <arvidschroeder@web.de>
Date: Thu, 17 Nov 2022 19:22:30 +0100
Subject: [PATCH] WIP reflection implementation

---
 primitive/infiniteplane.cpp |  4 +--
 primitive/triangle.cpp      |  2 +-
 shader/mirrorshader.cpp     |  3 +-
 shader/refractionshader.cpp | 70 ++++++++++++++++++++++++++++++++-----
 4 files changed, 66 insertions(+), 13 deletions(-)

diff --git a/primitive/infiniteplane.cpp b/primitive/infiniteplane.cpp
index 81bd973..a0851f2 100644
--- a/primitive/infiniteplane.cpp
+++ b/primitive/infiniteplane.cpp
@@ -28,9 +28,9 @@ bool InfinitePlane::intersect(Ray &ray) const {
 
   // Set the normal
   if (acos(dotProduct(ray.direction, this->normal)) > 0) {
-      ray.normal = this->normal;
+      ray.normal = normalized(this->normal);
   } else {
-      ray.normal = -1.0f * this->normal;
+      ray.normal = normalized((-1.0f * this->normal));
   }
 
 
diff --git a/primitive/triangle.cpp b/primitive/triangle.cpp
index b3cb2bd..e0dd877 100644
--- a/primitive/triangle.cpp
+++ b/primitive/triangle.cpp
@@ -101,7 +101,7 @@ bool Triangle::intersect(Ray &ray) const {
     return false;
 
   // Calculate the normal
-  ray.normal = crossProduct(edge1, edge1);
+  ray.normal = normalized(crossProduct(edge1, edge1));
 
   // Calculate the surface position
   ray.surface = u * this->surface[1] + v * this->surface[2] + (1 - u - v) * this->surface[0];
diff --git a/shader/mirrorshader.cpp b/shader/mirrorshader.cpp
index 28780db..35b5567 100644
--- a/shader/mirrorshader.cpp
+++ b/shader/mirrorshader.cpp
@@ -5,12 +5,11 @@ MirrorShader::MirrorShader() {}
 
 Color MirrorShader::shade(Scene const &scene, Ray const &ray) const {
     if (ray.getRemainingBounces() <= 0) {
-        return Color(0, 0, 0);
+        return Color(0, 255, 0);
     }
 
     Vector3d newDirection = ray.direction - 2 * dotProduct(ray.normal, ray.direction) * ray.normal;
 
-    //TODO: should we reset the ray or use a new ray? Regarding the count of bounces
     Ray mirroredRay = Ray(ray.origin + ray.length * ray.direction, newDirection);
     mirroredRay.setRemainingBounces(ray.getRemainingBounces() - 1);
 
diff --git a/shader/refractionshader.cpp b/shader/refractionshader.cpp
index 8a942c2..41ef265 100644
--- a/shader/refractionshader.cpp
+++ b/shader/refractionshader.cpp
@@ -1,3 +1,4 @@
+#include <iostream>
 #include "scene/scene.h"
 #include "shader/refractionshader.h"
 
@@ -11,19 +12,72 @@ Color RefractionShader::shade(Scene const &scene, Ray const &ray) const {
     // Send out a new refracted ray into the scene; recursively call traceRay()
 
     if (ray.getRemainingBounces() < 1) {
-        return Color(0,0,0);
+        return Color(0,255,0);
+    }
+    
+    auto eta1 = indexOutside;
+    auto eta2 = indexInside;
+
+
+    Vector3d v = normalized(ray.direction);
+    Vector3d n = normalized(ray.normal);
+
+    // Check whether we are entering or leaving the object
+    if (acos(dotProduct(v, n)) < PI/2.0f) {
+        eta1 = indexInside;
+        eta2 = indexOutside;
     }
 
-    Vector3d n = ray.normal;
-    double root = sqrt(1 - (indexOutside*indexOutside*(1 - dotProduct(ray.direction, n)
-            *dotProduct(ray.direction, n)))/(indexInside*indexInside));
+    // Calculate refraction percentage
+    float denominator = 1.0f -
+            (pow(eta1, 2) * (1 - pow(dotProduct(v, n), 2)) /
+             pow(eta2, 2));
 
-    Vector3d t = (indexOutside/indexInside)*(ray.direction - dotProduct(ray.direction, n) * n)- n * root;
+    // Check whether there is any refracted ray at all or whether we have total internal reflection
+    if (denominator <= 0) {
+        Vector3d newDirection = v - 2.0f * dotProduct(n, v) * n;
 
-    Ray reflectionRay = Ray(ray.origin + ray.length * ray.direction, t);
-    reflectionRay.setRemainingBounces(ray.getRemainingBounces()-1);
+        Ray mirroredRay = Ray(ray.origin + ray.length * v, newDirection);
+        mirroredRay.setRemainingBounces(ray.getRemainingBounces() - 1);
 
-    return scene.traceRay(reflectionRay);
+        return scene.traceRay(mirroredRay);
+    }
+
+    // Calculate refracted ray direction t
+    Vector3d t = normalized(
+            eta1 / eta2 *
+            (v - dotProduct(v, n) * n) -
+            n * sqrt(denominator));
+
+    // Calculate reflected ray direction
+    Vector3d cosTheta1 = crossProduct(v, n);
+    Vector3d cosTheta2 = -1.0f * crossProduct(n, t);
+
+    Vector3d polarizationParallel = (eta2 * cosTheta1 - eta1 * cosTheta2) /
+            (eta2 * cosTheta1 + eta1 * cosTheta2);
+    Vector3d polarizationOrthogonal = (eta1 * cosTheta1 - eta2 * cosTheta2) /
+                                (eta1 * cosTheta1 + eta2 * cosTheta2);
+
+    Vector3d reflectionVector = normalized(
+            0.5f * (polarizationParallel * polarizationParallel + polarizationOrthogonal * polarizationOrthogonal));
+
+    // Calculate rays
+    Vector3d rayOrigin = ray.origin + ray.length * ray.direction;
+    Ray refractionRay = Ray(rayOrigin, t);
+    Ray reflectionRay = Ray(rayOrigin, reflectionVector);
+
+    int remainingBounces = ray.getRemainingBounces() - 1;
+
+    refractionRay.setRemainingBounces(remainingBounces);
+    reflectionRay.setRemainingBounces(remainingBounces);
+
+    // Calculate Color
+    Color refractionColor = scene.traceRay(refractionRay);
+    Color reflectionColor = scene.traceRay(reflectionRay);
+
+    Color resultingColor = denominator * refractionColor + (1-denominator) * reflectionColor;
+
+    return resultingColor;
 }
 
 bool RefractionShader::isTransparent() const { return true; }