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

plane.hpp

@@ -14,17 +14,28 @@ public:
   vec3 m_point;
   vec3 m_normal;
   
-  Plane(Material * mat = NULL): Figure(mat), m_point(vec3(0.0f)), m_normal(vec3(0.0f, 0.0f, 1.0f)) { }
+  Plane(Material * mat = NULL): Figure(mat), m_point(vec3(0.0f)), m_normal(vec3(0.0f, 0.0f, 1.0f)) {
+    calculate_inv_area();
+  }
 
-  Plane(float x, float y, float z, float nx, float ny, float nz, Material * mat = NULL): Figure(mat), m_point(vec3(x, y, z)), m_normal(normalize(vec3(nx, ny, nz))) { }
+  Plane(float x, float y, float z, float nx, float ny, float nz, Material * mat = NULL):
+    Figure(mat),
+    m_point(vec3(x, y, z)),
+    m_normal(normalize(vec3(nx, ny, nz)))
+  {
+    calculate_inv_area();
+  }
 
   Plane(vec3 _p, vec3 _n, Material * mat = NULL): Figure(mat), m_point(_p), m_normal(normalize(_n)) { }
 
   virtual ~Plane() { }
 
   virtual bool intersect(Ray & r, float & t) const;
-
   virtual vec3 normal_at_int(Ray & r, float & t) const;
+  virtual vec3 sample_at_surface() const;
+
+protected:
+  virtual void calculate_inv_area();
 };