From b354f7f87d61f576cf1f8c04e68642890cb79e41 Mon Sep 17 00:00:00 2001
From: SirLynix <lynix680@gmail.com>
Date: Fri, 17 Mar 2023 19:24:57 +0100
Subject: [PATCH] Math/Quaternion: Fix RotationBetween not handling parallel
 vectors

---
 include/Nazara/Math/Quaternion.inl | 29 ++++++++++++++++++++++++-----
 1 file changed, 24 insertions(+), 5 deletions(-)

diff --git a/include/Nazara/Math/Quaternion.inl b/include/Nazara/Math/Quaternion.inl
index c3b1f9431..af2835d5d 100644
--- a/include/Nazara/Math/Quaternion.inl
+++ b/include/Nazara/Math/Quaternion.inl
@@ -268,11 +268,30 @@ namespace Nz
 	template<typename T>
 	Quaternion<T>& Quaternion<T>::MakeRotationBetween(const Vector3<T>& from, const Vector3<T>& to)
 	{
-		// Based on: http://lolengine.net/blog/2013/09/18/beautiful-maths-quaternion-from-vectors
-		T norm = std::sqrt(from.GetSquaredLength() * to.GetSquaredLength());
-		Vector3<T> crossProduct = from.CrossProduct(to);
-		Set(norm + from.DotProduct(to), crossProduct.x, crossProduct.y, crossProduct.z);
-		return Normalize();
+		T dot = from.DotProduct(to);
+		if (dot < T(-0.999999))
+		{
+			Vector3<T> crossProduct;
+			if (from.DotProduct(Vector3<T>::UnitX()) < T(0.999999))
+				crossProduct = Vector3<T>::UnitX().CrossProduct(from);
+			else
+				crossProduct = Vector3<T>::UnitY().CrossProduct(from);
+
+			crossProduct.Normalize();
+			Set(Pi<T>, crossProduct);
+			return *this;
+		}
+		else if (dot > T(0.999999))
+		{
+			Set(T(1.0), T(0.0), T(0.0), T(0.0));
+			return *this;
+		}
+		else
+		{
+			Vector3<T> crossProduct = from.CrossProduct(to);
+			Set(T(1) + dot, crossProduct.x, crossProduct.y, crossProduct.z);
+			return Normalize();
+		}
 	}
 
 	/*!