text: ///////////////////////////////////////////////////////////////////////////////////////////////////
  // OpenGL Mathematics Copyright (c) 2005 - 2010 G-Truc Creation (www.g-truc.net)
  ///////////////////////////////////////////////////////////////////////////////////////////////////
  // Created : 2005-12-30
  // Updated : 2006-11-13
  // Licence : This source is under MIT License
  // File    : glm/gtx/vector_angle.hpp
  ///////////////////////////////////////////////////////////////////////////////////////////////////
  // Dependency:
  // - GLM core
  // - GLM_GTX_quaternion
  // - GLM_GTX_epsilon
  ///////////////////////////////////////////////////////////////////////////////////////////////////
  
  #ifndef glm_gtx_vector_angle
  #define glm_gtx_vector_angle
  
  // Dependency:
  #include "../glm.hpp"
  #include "../gtx/quaternion.hpp"
  #include "../gtx/epsilon.hpp"
  
  namespace glm
  {
  	namespace test{
  		void main_gtx_vector_angle();
  	}//namespace test
  
      namespace gtx{
  	//! GLM_GTX_vector_angle extension: Compute angle between vectors
      namespace vector_angle
      {
  		using namespace quaternion;
  		using namespace epsilon;
  
  		//! Returns the absolute angle between x and y.
  		//! Parameters need to be normalized.
  		//! From GLM_GTX_vector_angle extension
  		template <typename vecType> 
  		typename vecType::value_type angle(
  			vecType const & x, 
  			vecType const & y);
  
  		//! Returns the oriented angle between x and y 
  		//! Parameters need to be normalized.
  		//! From GLM_GTX_vector_angle extension.
  		template <typename vecType> 
  		typename vecType::value_type orientedAngle(
  			vecType const & x, 
  			vecType const & y);
  
  		//! Returns the orientation of a two vector base from a normal.
  		//! Parameters need to be normalized.
  		//! From GLM_GTX_vector_angle extension.
  		template <typename vecType>
  		typename vecType::value_type orientedAngleFromRef(
  			vecType const & x,
  			vecType const & y,
  			detail::tvec3<typename vecType::value_type> const & ref);
      }//namespace vector_angle
      }//namespace gtx
  }//namespace glm
  
  #include "vector_angle.inl"
  
  namespace glm{using namespace gtx::vector_angle;}
  
  #endif//glm_gtx_vector_angle
  