text: ///////////////////////////////////////////////////////////////////////////////////
  /// OpenGL Mathematics (glm.g-truc.net)
  ///
  /// Copyright (c) 2005 - 2012 G-Truc Creation (www.g-truc.net)
  /// Permission is hereby granted, free of charge, to any person obtaining a copy
  /// of this software and associated documentation files (the "Software"), to deal
  /// in the Software without restriction, including without limitation the rights
  /// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  /// copies of the Software, and to permit persons to whom the Software is
  /// furnished to do so, subject to the following conditions:
  /// 
  /// The above copyright notice and this permission notice shall be included in
  /// all copies or substantial portions of the Software.
  /// 
  /// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  /// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  /// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  /// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  /// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  /// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  /// THE SOFTWARE.
  ///
  /// @ref core
  /// @file glm/core/func_geometric.hpp
  /// @date 2008-08-03 / 2011-06-14
  /// @author Christophe Riccio
  ///
  /// @see <a href="http://www.opengl.org/registry/doc/GLSLangSpec.4.20.8.pdf">GLSL 4.20.8 specification, section 8.5 Geometric Functions</a>
  /// 
  /// @defgroup core_func_geometric Geometric functions
  /// @ingroup core
  /// 
  /// These operate on vectors as vectors, not component-wise.
  ///////////////////////////////////////////////////////////////////////////////////
  
  #ifndef glm_core_func_geometric
  #define glm_core_func_geometric GLM_VERSION
  
  namespace glm
  {
  	/// @addtogroup core_func_geometric
  	/// @{
  
  	/// Returns the length of x, i.e., sqrt(x * x).
      /// 
  	/// @tparam genType Floating-point vector types.
  	/// 
      /// @see <a href="http://www.opengl.org/sdk/docs/manglsl/xhtml/length.xml">GLSL length man page</a>
      /// @see <a href="http://www.opengl.org/registry/doc/GLSLangSpec.4.20.8.pdf">GLSL 4.20.8 specification, section 8.5 Geometric Functions</a>
  	template <typename genType> 
          typename genType::value_type length(
  		genType const & x); 
  
  	/// Returns the distance betwwen p0 and p1, i.e., length(p0 - p1).
  	///
  	/// @tparam genType Floating-point vector types.
      /// 
      /// @see <a href="http://www.opengl.org/sdk/docs/manglsl/xhtml/distance.xml">GLSL distance man page</a>
      /// @see <a href="http://www.opengl.org/registry/doc/GLSLangSpec.4.20.8.pdf">GLSL 4.20.8 specification, section 8.5 Geometric Functions</a>
  	template <typename genType> 
  	typename genType::value_type distance(
  		genType const & p0, 
  		genType const & p1);
  
  	/// Returns the dot product of x and y, i.e., result = x * y.
  	///
  	/// @tparam genType Floating-point vector types.
      /// 
      /// @see <a href="http://www.opengl.org/sdk/docs/manglsl/xhtml/dot.xml">GLSL dot man page</a>
      /// @see <a href="http://www.opengl.org/registry/doc/GLSLangSpec.4.20.8.pdf">GLSL 4.20.8 specification, section 8.5 Geometric Functions</a>
      template <typename genType> 
  	typename genType::value_type dot(
  		genType const & x, 
  		genType const & y);
  
  	/// Returns the cross product of x and y.
  	///
  	/// @tparam valType Floating-point scalar types.
      /// 
      /// @see <a href="http://www.opengl.org/sdk/docs/manglsl/xhtml/cross.xml">GLSL cross man page</a>
      /// @see <a href="http://www.opengl.org/registry/doc/GLSLangSpec.4.20.8.pdf">GLSL 4.20.8 specification, section 8.5 Geometric Functions</a>
      template <typename valType> 
  	detail::tvec3<valType> cross(
  		detail::tvec3<valType> const & x, 
  		detail::tvec3<valType> const & y);
  
  	/// Returns a vector in the same direction as x but with length of 1.
      /// 
      /// @see <a href="http://www.opengl.org/sdk/docs/manglsl/xhtml/normalize.xml">GLSL normalize man page</a>
      /// @see <a href="http://www.opengl.org/registry/doc/GLSLangSpec.4.20.8.pdf">GLSL 4.20.8 specification, section 8.5 Geometric Functions</a>
  	template <typename genType> 
  	genType normalize(
  		genType const & x);
  
  	/// If dot(Nref, I) < 0.0, return N, otherwise, return -N.
  	///
  	/// @tparam genType Floating-point vector types.
      /// 
      /// @see <a href="http://www.opengl.org/sdk/docs/manglsl/xhtml/faceforward.xml">GLSL faceforward man page</a>
      /// @see <a href="http://www.opengl.org/registry/doc/GLSLangSpec.4.20.8.pdf">GLSL 4.20.8 specification, section 8.5 Geometric Functions</a>
      template <typename genType> 
  	genType faceforward(
  		genType const & N, 
  		genType const & I, 
  		genType const & Nref);
    
  	/// For the incident vector I and surface orientation N, 
  	/// returns the reflection direction : result = I - 2.0 * dot(N, I) * N.
  	///
  	/// @tparam genType Floating-point vector types.
      /// 
      /// @see <a href="http://www.opengl.org/sdk/docs/manglsl/xhtml/reflect.xml">GLSL reflect man page</a>
      /// @see <a href="http://www.opengl.org/registry/doc/GLSLangSpec.4.20.8.pdf">GLSL 4.20.8 specification, section 8.5 Geometric Functions</a>
      template <typename genType> 
  	genType reflect(
  		genType const & I, 
  		genType const & N);
    
  	/// For the incident vector I and surface normal N, 
  	/// and the ratio of indices of refraction eta, 
  	/// return the refraction vector.
  	///
  	/// @tparam genType Floating-point vector types.
      /// 
      /// @see <a href="http://www.opengl.org/sdk/docs/manglsl/xhtml/refract.xml">GLSL refract man page</a>
      /// @see <a href="http://www.opengl.org/registry/doc/GLSLangSpec.4.20.8.pdf">GLSL 4.20.8 specification, section 8.5 Geometric Functions</a>
      template <typename genType> 
  	genType refract(
  		genType const & I, 
  		genType const & N, 
  		typename genType::value_type const & eta);
  
  	/// @}
  }//namespace glm
  
  #include "func_geometric.inl"
  
  #endif//glm_core_func_geometric
  