sphere and disk area lights mostly ready (I think :S).

sphere.cpp

@@ -1,4 +1,8 @@
+#include <iostream>
+#include <glm/gtc/constants.hpp>
+
 #include "sphere.hpp"
+#include "sampling.hpp"
 
 using namespace glm;
 
@@ -38,3 +42,23 @@ vec3 Sphere::normal_at_int(Ray & r, float & t) const {
   vec3 i = vec3(r.m_origin + (t * r.m_direction));
   return normalize(vec3((i - m_center) / m_radius));
 }
+
+vec3 Sphere::sample_at_surface() const {
+  float theta;
+  float u, sqrt1muu, x, y, z;
+
+  // Sampling formula from Wolfram Mathworld:
+  // http://mathworld.wolfram.com/SpherePointPicking.html
+  theta = random01()* (2.0f * pi<float>());
+  u = (random01() * 2.0f) - 1.0f;
+  sqrt1muu = glm::sqrt(1.0f - (u * u));
+  x = m_radius * sqrt1muu * cos(theta);
+  y = m_radius * sqrt1muu * sin(theta);
+  z = m_radius * u;
+
+  return vec3(x, y, z) + m_center;
+}
+
+void Sphere::calculate_inv_area() {
+  m_inv_area = 1.0f / (4.0 * pi<float>() * (m_radius * m_radius));
+}