From 0d42f4a32030029fd20eb098dfa6d3096622780e Mon Sep 17 00:00:00 2001
From: Christophe Riccio <mail@g-truc.net>
Date: Sun, 7 Sep 2014 19:56:24 +0200
Subject: [PATCH] Added vec3 slerp #237

---
 glm/gtx/rotate_vector.hpp | 13 +++++++++++++
 glm/gtx/rotate_vector.inl | 22 ++++++++++++++++++++++
 readme.txt                |  1 +
 3 files changed, 36 insertions(+)

diff --git a/glm/gtx/rotate_vector.hpp b/glm/gtx/rotate_vector.hpp
index 06eaee01e..a8835f319 100644
--- a/glm/gtx/rotate_vector.hpp
+++ b/glm/gtx/rotate_vector.hpp
@@ -51,6 +51,19 @@ namespace glm
 	/// @addtogroup gtx_rotate_vector
 	/// @{
 
+	/// Returns the length of the quaternion.
+	/// 
+	/// @param x A first vector
+	/// @param y A second vector
+	/// @param a Interpolation factor. The interpolation is defined beyond the range [0, 1].
+	/// 
+	/// @see gtc_quaternion
+	template <typename T, precision P>
+	GLM_FUNC_DECL detail::tvec3<T, P> slerp(
+		detail::tvec3<T, P> const & x,
+		detail::tvec3<T, P> const & y,
+		T const & a);
+
 	//! Rotate a two dimensional vector.
 	//! From GLM_GTX_rotate_vector extension.
 	template <typename T, precision P>
diff --git a/glm/gtx/rotate_vector.inl b/glm/gtx/rotate_vector.inl
index 0978bd527..8e190c58f 100644
--- a/glm/gtx/rotate_vector.inl
+++ b/glm/gtx/rotate_vector.inl
@@ -9,6 +9,28 @@
 
 namespace glm
 {
+	template <typename T, precision P>
+	GLM_FUNC_QUALIFIER detail::tvec3<T, P> slerp
+	(
+		detail::tvec3<T, P> const & x,
+		detail::tvec3<T, P> const & y,
+		T const & a
+	)
+	{
+		// get cosine of angle between vectors (-1 -> 1)
+		T CosAlpha = dot(x, y);
+		// get angle (0 -> pi)
+		T Alpha = acos(CosAlpha);
+		// get sine of angle between vectors (0 -> 1)
+		T SinAlpha = sin(Alpha);
+		// this breaks down when SinAlpha = 0, i.e. Alpha = 0 or pi
+		T t1 = sin((static_cast<T>(1) - a) * Alpha) / SinAlpha;
+		T t2 = sin(a * Alpha) / sinAlpha;
+
+		// interpolate src vectors
+		return x * t1 + y * t2;
+	}
+
 	template <typename T, precision P>
 	GLM_FUNC_QUALIFIER detail::tvec2<T, P> rotate
 	(
diff --git a/readme.txt b/readme.txt
index 03d37a52a..dcc6d907e 100644
--- a/readme.txt
+++ b/readme.txt
@@ -48,6 +48,7 @@ GLM 0.9.6.0: 2014-XX-XX
 - Added *vec1 support to *vec2 types
 - Limited extended integer type redifinition (#233)
 - Improved linearRand: support precision and integers (#230)
+- Added vec3 slerp (#237)
 
 ================================================================================
 GLM 0.9.5.5: 2014-XX-XX