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diff --git a/Source/external/Box2D/Dynamics/Joints/b2GearJoint.h b/Source/external/Box2D/Dynamics/Joints/b2GearJoint.h
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+/*
+* Copyright (c) 2006-2011 Erin Catto http://www.box2d.org
+*
+* This software is provided 'as-is', without any express or implied
+* warranty.  In no event will the authors be held liable for any damages
+* arising from the use of this software.
+* Permission is granted to anyone to use this software for any purpose,
+* including commercial applications, and to alter it and redistribute it
+* freely, subject to the following restrictions:
+* 1. The origin of this software must not be misrepresented; you must not
+* claim that you wrote the original software. If you use this software
+* in a product, an acknowledgment in the product documentation would be
+* appreciated but is not required.
+* 2. Altered source versions must be plainly marked as such, and must not be
+* misrepresented as being the original software.
+* 3. This notice may not be removed or altered from any source distribution.
+*/
+
+#ifndef B2_GEAR_JOINT_H
+#define B2_GEAR_JOINT_H
+
+#include "Box2D/Dynamics/Joints/b2Joint.h"
+
+/// Gear joint definition. This definition requires two existing
+/// revolute or prismatic joints (any combination will work).
+struct b2GearJointDef : public b2JointDef
+{
+	b2GearJointDef()
+	{
+		type = e_gearJoint;
+		joint1 = nullptr;
+		joint2 = nullptr;
+		ratio = 1.0f;
+	}
+
+	/// The first revolute/prismatic joint attached to the gear joint.
+	b2Joint* joint1;
+
+	/// The second revolute/prismatic joint attached to the gear joint.
+	b2Joint* joint2;
+
+	/// The gear ratio.
+	/// @see b2GearJoint for explanation.
+	float32 ratio;
+};
+
+/// A gear joint is used to connect two joints together. Either joint
+/// can be a revolute or prismatic joint. You specify a gear ratio
+/// to bind the motions together:
+/// coordinate1 + ratio * coordinate2 = constant
+/// The ratio can be negative or positive. If one joint is a revolute joint
+/// and the other joint is a prismatic joint, then the ratio will have units
+/// of length or units of 1/length.
+/// @warning You have to manually destroy the gear joint if joint1 or joint2
+/// is destroyed.
+class b2GearJoint : public b2Joint
+{
+public:
+	b2Vec2 GetAnchorA() const override;
+	b2Vec2 GetAnchorB() const override;
+
+	b2Vec2 GetReactionForce(float32 inv_dt) const override;
+	float32 GetReactionTorque(float32 inv_dt) const override;
+
+	/// Get the first joint.
+	b2Joint* GetJoint1() { return m_joint1; }
+
+	/// Get the second joint.
+	b2Joint* GetJoint2() { return m_joint2; }
+
+	/// Set/Get the gear ratio.
+	void SetRatio(float32 ratio);
+	float32 GetRatio() const;
+
+	/// Dump joint to dmLog
+	void Dump() override;
+
+protected:
+
+	friend class b2Joint;
+	b2GearJoint(const b2GearJointDef* data);
+
+	void InitVelocityConstraints(const b2SolverData& data) override;
+	void SolveVelocityConstraints(const b2SolverData& data) override;
+	bool SolvePositionConstraints(const b2SolverData& data) override;
+
+	b2Joint* m_joint1;
+	b2Joint* m_joint2;
+
+	b2JointType m_typeA;
+	b2JointType m_typeB;
+
+	// Body A is connected to body C
+	// Body B is connected to body D
+	b2Body* m_bodyC;
+	b2Body* m_bodyD;
+
+	// Solver shared
+	b2Vec2 m_localAnchorA;
+	b2Vec2 m_localAnchorB;
+	b2Vec2 m_localAnchorC;
+	b2Vec2 m_localAnchorD;
+
+	b2Vec2 m_localAxisC;
+	b2Vec2 m_localAxisD;
+
+	float32 m_referenceAngleA;
+	float32 m_referenceAngleB;
+
+	float32 m_constant;
+	float32 m_ratio;
+
+	float32 m_impulse;
+
+	// Solver temp
+	int32 m_indexA, m_indexB, m_indexC, m_indexD;
+	b2Vec2 m_lcA, m_lcB, m_lcC, m_lcD;
+	float32 m_mA, m_mB, m_mC, m_mD;
+	float32 m_iA, m_iB, m_iC, m_iD;
+	b2Vec2 m_JvAC, m_JvBD;
+	float32 m_JwA, m_JwB, m_JwC, m_JwD;
+	float32 m_mass;
+};
+
+#endif