From fabf01ff393a87ea9dea6498b1617f17261e2261 Mon Sep 17 00:00:00 2001
From: Dan Weatherford <sabretooth@gmail.com>
Date: Fri, 11 Jun 2021 01:20:57 -0500
Subject: [PATCH] aux/math: Add math_quat_slerp()

---
 src/xrt/auxiliary/math/m_api.h    |  9 +++++++++
 src/xrt/auxiliary/math/m_base.cpp | 12 ++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/src/xrt/auxiliary/math/m_api.h b/src/xrt/auxiliary/math/m_api.h
index 0e32c02f1..0e23ab42c 100644
--- a/src/xrt/auxiliary/math/m_api.h
+++ b/src/xrt/auxiliary/math/m_api.h
@@ -290,6 +290,15 @@ void
 math_quat_rotate_derivative(const struct xrt_quat *rot, const struct xrt_vec3 *deriv, struct xrt_vec3 *result);
 
 
+/*!
+ * Slerp (spherical linear interpolation) between two quaternions
+ *
+ * @relates xrt_quat
+ * @ingroup aux_math
+ */
+void
+math_quat_slerp(const struct xrt_quat *left, const struct xrt_quat *right, float t, struct xrt_quat *result);
+
 /*
  *
  * Matrix functions
diff --git a/src/xrt/auxiliary/math/m_base.cpp b/src/xrt/auxiliary/math/m_base.cpp
index c31da1eb4..c7a827e06 100644
--- a/src/xrt/auxiliary/math/m_base.cpp
+++ b/src/xrt/auxiliary/math/m_base.cpp
@@ -299,6 +299,18 @@ math_quat_rotate_derivative(const struct xrt_quat *quat, const struct xrt_vec3 *
 	*result = ret;
 }
 
+extern "C" void
+math_quat_slerp(const struct xrt_quat *left, const struct xrt_quat *right, float t, struct xrt_quat *result)
+{
+	assert(left != NULL);
+	assert(right != NULL);
+	assert(result != NULL);
+
+	auto l = copy(left);
+	auto r = copy(right);
+
+	map_quat(*result) = l.slerp(t, r);
+}
 
 /*
  *