text: /// @ref gtx_intersect
  
  namespace glm
  {
  	template<typename genType>
  	GLM_FUNC_QUALIFIER bool intersectRayPlane
  	(
  		genType const& orig, genType const& dir,
  		genType const& planeOrig, genType const& planeNormal,
  		typename genType::value_type & intersectionDistance
  	)
  	{
  		typename genType::value_type d = glm::dot(dir, planeNormal);
  		typename genType::value_type Epsilon = std::numeric_limits<typename genType::value_type>::epsilon();
  
  		if(glm::abs(d) > Epsilon)  // if dir and planeNormal are not perpendicular
  		{
  			typename genType::value_type const tmp_intersectionDistance = 	glm::dot(planeOrig - orig, planeNormal) / d;
  			if (tmp_intersectionDistance > static_cast<typename genType::value_type>(0)) { // allow only intersections
  				intersectionDistance = tmp_intersectionDistance;
  				return true;
  			}
  		}
  
  		return false;
  	}
  
  	template<typename T, qualifier Q>
  	GLM_FUNC_QUALIFIER bool intersectRayTriangle
  	(
  		vec<3, T, Q> const& orig, vec<3, T, Q> const& dir,
  		vec<3, T, Q> const& vert0, vec<3, T, Q> const& vert1, vec<3, T, Q> const& vert2,
  		vec<2, T, Q>& baryPosition, T& distance
  	)
  	{
  		// find vectors for two edges sharing vert0
  		vec<3, T, Q> const edge1 = vert1 - vert0;
  		vec<3, T, Q> const edge2 = vert2 - vert0;
  
  		// begin calculating determinant - also used to calculate U parameter
  		vec<3, T, Q> const p = glm::cross(dir, edge2);
  
  		// if determinant is near zero, ray lies in plane of triangle
  		T const det = glm::dot(edge1, p);
  
  		vec<3, T, Q> Perpendicular(0);
  
  		if(det > std::numeric_limits<T>::epsilon())
  		{
  			// calculate distance from vert0 to ray origin
  			vec<3, T, Q> const dist = orig - vert0;
  
  			// calculate U parameter and test bounds
  			baryPosition.x = glm::dot(dist, p);
  			if(baryPosition.x < static_cast<T>(0) || baryPosition.x > det)
  				return false;
  
  			// prepare to test V parameter
  			Perpendicular = glm::cross(dist, edge1);
  
  			// calculate V parameter and test bounds
  			baryPosition.y = glm::dot(dir, Perpendicular);
  			if((baryPosition.y < static_cast<T>(0)) || ((baryPosition.x + baryPosition.y) > det))
  				return false;
  		}
  		else if(det < -std::numeric_limits<T>::epsilon())
  		{
  			// calculate distance from vert0 to ray origin
  			vec<3, T, Q> const dist = orig - vert0;
  
  			// calculate U parameter and test bounds
  			baryPosition.x = glm::dot(dist, p);
  			if((baryPosition.x > static_cast<T>(0)) || (baryPosition.x < det))
  				return false;
  
  			// prepare to test V parameter
  			Perpendicular = glm::cross(dist, edge1);
  
  			// calculate V parameter and test bounds
  			baryPosition.y = glm::dot(dir, Perpendicular);
  			if((baryPosition.y > static_cast<T>(0)) || (baryPosition.x + baryPosition.y < det))
  				return false;
  		}
  		else
  			return false; // ray is parallel to the plane of the triangle
  
  		T inv_det = static_cast<T>(1) / det;
  
  		// calculate distance, ray intersects triangle
  		distance = glm::dot(edge2, Perpendicular) * inv_det;
  		baryPosition *= inv_det;
  
  		return true;
  	}
  
  	template<typename genType>
  	GLM_FUNC_QUALIFIER bool intersectLineTriangle
  	(
  		genType const& orig, genType const& dir,
  		genType const& vert0, genType const& vert1, genType const& vert2,
  		genType & position
  	)
  	{
  		typename genType::value_type Epsilon = std::numeric_limits<typename genType::value_type>::epsilon();
  
  		genType edge1 = vert1 - vert0;
  		genType edge2 = vert2 - vert0;
  
  		genType Perpendicular = cross(dir, edge2);
  
  		typename genType::value_type det = dot(edge1, Perpendicular);
  
  		if (det > -Epsilon && det < Epsilon)
  			return false;
  		typename genType::value_type inv_det = typename genType::value_type(1) / det;
  
  		genType Tengant = orig - vert0;
  
  		position.y = dot(Tengant, Perpendicular) * inv_det;
  		if (position.y < typename genType::value_type(0) || position.y > typename genType::value_type(1))
  			return false;
  
  		genType Cotengant = cross(Tengant, edge1);
  
  		position.z = dot(dir, Cotengant) * inv_det;
  		if (position.z < typename genType::value_type(0) || position.y + position.z > typename genType::value_type(1))
  			return false;
  
  		position.x = dot(edge2, Cotengant) * inv_det;
  
  		return true;
  	}
  
  	template<typename genType>
  	GLM_FUNC_QUALIFIER bool intersectRaySphere
  	(
  		genType const& rayStarting, genType const& rayNormalizedDirection,
  		genType const& sphereCenter, const typename genType::value_type sphereRadiusSquared,
  		typename genType::value_type & intersectionDistance
  	)
  	{
  		typename genType::value_type Epsilon = std::numeric_limits<typename genType::value_type>::epsilon();
  		genType diff = sphereCenter - rayStarting;
  		typename genType::value_type t0 = dot(diff, rayNormalizedDirection);
  		typename genType::value_type dSquared = dot(diff, diff) - t0 * t0;
  		if( dSquared > sphereRadiusSquared )
  		{
  			return false;
  		}
  		typename genType::value_type t1 = sqrt( sphereRadiusSquared - dSquared );
  		intersectionDistance = t0 > t1 + Epsilon ? t0 - t1 : t0 + t1;
  		return intersectionDistance > Epsilon;
  	}
  
  	template<typename genType>
  	GLM_FUNC_QUALIFIER bool intersectRaySphere
  	(
  		genType const& rayStarting, genType const& rayNormalizedDirection,
  		genType const& sphereCenter, const typename genType::value_type sphereRadius,
  		genType & intersectionPosition, genType & intersectionNormal
  	)
  	{
  		typename genType::value_type distance;
  		if( intersectRaySphere( rayStarting, rayNormalizedDirection, sphereCenter, sphereRadius * sphereRadius, distance ) )
  		{
  			intersectionPosition = rayStarting + rayNormalizedDirection * distance;
  			intersectionNormal = (intersectionPosition - sphereCenter) / sphereRadius;
  			return true;
  		}
  		return false;
  	}
  
  	template<typename genType>
  	GLM_FUNC_QUALIFIER bool intersectLineSphere
  	(
  		genType const& point0, genType const& point1,
  		genType const& sphereCenter, typename genType::value_type sphereRadius,
  		genType & intersectionPoint1, genType & intersectionNormal1,
  		genType & intersectionPoint2, genType & intersectionNormal2
  	)
  	{
  		typename genType::value_type Epsilon = std::numeric_limits<typename genType::value_type>::epsilon();
  		genType dir = normalize(point1 - point0);
  		genType diff = sphereCenter - point0;
  		typename genType::value_type t0 = dot(diff, dir);
  		typename genType::value_type dSquared = dot(diff, diff) - t0 * t0;
  		if( dSquared > sphereRadius * sphereRadius )
  		{
  			return false;
  		}
  		typename genType::value_type t1 = sqrt( sphereRadius * sphereRadius - dSquared );
  		if( t0 < t1 + Epsilon )
  			t1 = -t1;
  		intersectionPoint1 = point0 + dir * (t0 - t1);
  		intersectionNormal1 = (intersectionPoint1 - sphereCenter) / sphereRadius;
  		intersectionPoint2 = point0 + dir * (t0 + t1);
  		intersectionNormal2 = (intersectionPoint2 - sphereCenter) / sphereRadius;
  		return true;
  	}
  }//namespace glm
  