From 66018249860d827550879dd59668b27843bbadae Mon Sep 17 00:00:00 2001
From: lisyarus <lisyarus@gmail.com>
Date: Thu, 20 Aug 2026 21:52:38 +0300
Subject: [PATCH] Fix NaN in quaternion slerp when slerping opposite
 quaternions

---
 libs/math/include/psemek/math/quaternion.hpp | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/libs/math/include/psemek/math/quaternion.hpp b/libs/math/include/psemek/math/quaternion.hpp
index b341a9d2..fff1573f 100644
--- a/libs/math/include/psemek/math/quaternion.hpp
+++ b/libs/math/include/psemek/math/quaternion.hpp
@@ -265,8 +265,10 @@ namespace psemek::math
 		auto const d = dot(q0.coords, q1.coords);
 
 		// prevent division by zero
-		if (d >= T{1})
-			return quaternion<T>{lerp(q0.coords, q1.coords, t)};
+		if (d >= T{ 1})
+			return quaternion<T>{lerp(q0.coords,  q1.coords, t)};
+		if (d <= T{-1})
+			return quaternion<T>{lerp(q0.coords, -q1.coords, t)};
 
 		auto const omega = acos(abs(d));