From 7a2c1f3713be127f6e4361fd8f426e78e8965bab Mon Sep 17 00:00:00 2001
From: Roland Hieber <rohieb@rohieb.name>
Date: Wed, 20 Jan 2010 02:34:16 +0100
Subject: [PATCH] solution to assignment 2.2 b): surface normalsD

---
 InfinitePlane.cxx |  9 +++++----
 Sphere.cxx        | 19 +++++++++++++++----
 Triangle.cxx      | 27 +++++++++++++++------------
 3 files changed, 35 insertions(+), 20 deletions(-)

diff --git a/InfinitePlane.cxx b/InfinitePlane.cxx
index 442da19..54c9570 100644
--- a/InfinitePlane.cxx
+++ b/InfinitePlane.cxx
@@ -1,11 +1,11 @@
 #include "InfinitePlane.hxx"
 
 InfinitePlane::InfinitePlane(const Vec3f& a, const Vec3f& n, Shader* shader)
-  : Primitive(shader), 
+  : Primitive(shader),
     m_a(a),
     m_n(n)
 {
-  
+
 }
 
 InfinitePlane::~InfinitePlane()
@@ -17,7 +17,7 @@ InfinitePlane::Intersect(Ray& ray)
 {
   Vec3f diff = m_a - ray.origin();
   float t = diff.dot(m_n) / ray.direction().dot(m_n);
-  if (t < 1e-5 || t > ray.t()) 
+  if (t < 1e-5 || t > ray.t())
     return false;
   ray.setT(t);
   return true;
@@ -26,5 +26,6 @@ InfinitePlane::Intersect(Ray& ray)
 Vec3f
 InfinitePlane::GetNormal(Ray& ray)
 {
-  return Vec3f();
+  // We already have the surface normal
+  return m_n;
 }
diff --git a/Sphere.cxx b/Sphere.cxx
index 3c19afa..5706cc3 100644
--- a/Sphere.cxx
+++ b/Sphere.cxx
@@ -1,7 +1,7 @@
 #include "Sphere.hxx"
 
 Sphere::Sphere(const Vec3f& center, float radius, Shader* shader)
-  : Primitive(shader), 
+  : Primitive(shader),
     m_center(center),
     m_radius(radius)
 {
@@ -20,12 +20,12 @@ Sphere::Intersect(Ray& ray)
 
   if( B*B-4*A*C < 0 )
     return false;
-  
+
   float root = sqrtf(B*B-4*A*C);
   float t = (-B-root)/(2.0f*A);
   if(t > ray.t())
     return false;
-      
+
   if( t < 1e-6 )
     {
       t = (-B+root)/(2.0f*A);
@@ -39,5 +39,16 @@ Sphere::Intersect(Ray& ray)
 Vec3f
 Sphere::GetNormal(Ray& ray)
 {
-  return Vec3f();
+  // We don't want to modify the ray (probably this is not needed, but I am
+  // too lazy to think about it now ...)
+  Ray tempRay = ray;
+
+  // Surface normal is the difference between intersection and center point
+  Intersect(tempRay);
+  // intersection
+  Vec3f i = tempRay.origin() + tempRay.direction() * tempRay.t();
+  // normal
+  Vec3f n = (i - m_center);
+  n.normalize();
+  return n;
 }
diff --git a/Triangle.cxx b/Triangle.cxx
index 761abcb..456c6d8 100644
--- a/Triangle.cxx
+++ b/Triangle.cxx
@@ -20,40 +20,43 @@ Triangle::Intersect(Ray& ray)
 {
   const Vec3f edge1 = m_b-m_a;
   const Vec3f edge2 = m_c-m_a;
-  
+
   const Vec3f pvec = ray.direction().cross(edge2);
-  
+
   const float det = edge1.dot(pvec);
   if (fabs(det) < Epsilon) return false;
-  
+
   const float inv_det = 1.0f / det;
-  
+
   const Vec3f tvec = ray.origin()-m_a;
   float lambda = tvec.dot( pvec );
   lambda *= inv_det;
-    
-  if (lambda < 0.0f || lambda > 1.0f) 
+
+  if (lambda < 0.0f || lambda > 1.0f)
     return false;
 
   const Vec3f qvec = tvec.cross(edge1);
   float mue = ray.direction().dot(qvec);
   mue *= inv_det;
-  
-  if (mue < 0.0f || mue+lambda > 1.0f) 
+
+  if (mue < 0.0f || mue+lambda > 1.0f)
     return false;
 
   float f = edge2.dot(qvec);
   f *= inv_det;
-  if (ray.t() <= f || f <  1e-4  ) 
+  if (ray.t() <= f || f <  1e-4  )
     return false;
-  
+
   ray.setT(f);
-    
+
   return true;
 }
 
 Vec3f
 Triangle::GetNormal(Ray& ray)
 {
-  return Vec3f();
+  // normal is cross product of spanning vectors
+  Vec3f n = (m_c - m_a) % (m_c - m_b);
+  n.normalize();
+  return n;
 }
-- 
2.20.1