Added new ray-sphere intersection

This version uses a geometric method (usually faster) and doesn't
calculate the intersection position and normal, only the distance.

glm/gtx/intersect.hpp

@@ -68,6 +68,15 @@ namespace glm
 		genType const & vert0, genType const & vert1, genType const & vert2,
 		genType & position);
 
+	//! Compute the intersection distance of a ray and a sphere. 
+	//! The ray direction vector is unit length.
+	//! From GLM_GTX_intersect extension.
+	template <typename genType>
+	bool intersectRaySphere(
+		genType const & rayStarting, genType const & rayNormalizedDirection,
+		genType const & sphereCenter, const typename genType::value_type sphereRadiusSquered,
+		typename genType::value_type & intersectionDistance);
+
     //! Compute the intersection of a ray and a sphere.
 	//! From GLM_GTX_intersect extension.
 	template <typename genType>

glm/gtx/intersect.inl

@@ -127,6 +127,27 @@ namespace glm
 		return true;
 	}
 
+	template <typename genType>
+	GLM_FUNC_QUALIFIER bool intersectRaySphere
+	(
+		genType const & rayStarting, genType const & rayNormalizedDirection,
+		genType const & sphereCenter, const typename genType::value_type sphereRadiusSquered,
+		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 > sphereRadiusSquered )
+		{
+			return false;
+		}
+		typename genType::value_type t1 = sqrt( sphereRadiusSquered - dSquared );
+		intersectionDistance = t0 > t1 + Epsilon ? t0 - t1 : t0 + t1;
+		return intersectionDistance > Epsilon;
+	}
+
 	template <typename genType>
 	GLM_FUNC_QUALIFIER bool intersectRaySphere
 	(