added getNormalAt() to Shape & Sphere, trying to get basic lighting

git-svn-id: svn://anubis/fart/trunk@44 7f9b0f55-74a9-4bce-be96-3c2cd072584d

util/Vector.cc

@@ -26,14 +26,14 @@ Vector & Vector::normalize()
     return *this;
 }
 
-double Vector::mag()
+double Vector::mag() const
 {
     return sqrt(m_array[0] * m_array[0]
               + m_array[1] * m_array[1]
               + m_array[2] * m_array[2]);
 }
 
-double Vector::mag2()
+double Vector::mag2() const
 {
     return m_array[0] * m_array[0]
          + m_array[1] * m_array[1]

util/Vector.h

@@ -12,8 +12,8 @@ class Vector
         double & operator[](int idx) { return m_array[idx]; }
         double operator[](int idx) const { return m_array[idx]; }
         Vector & normalize();
-        double mag();
-        double mag2();
+        double mag() const;
+        double mag2() const;
 
     private:
         double  m_array[3];