/*
* Copyright (c) 2006-2007 Erin Catto http://www.gphysics.com
*
* 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>

class b2RevoluteJoint;
class b2PrismaticJoint;

/// Gear joint definition. This definition requires two existing
/// revolute or prismatic joints (any combination will work).
/// The provided joints must attach a dynamic body to a static body.
struct b2GearJointDef : public b2JointDef
{
	b2GearJointDef()
	{
		type = e_gearJoint;
		joint1 = NULL;
		joint2 = NULL;
		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 The revolute and prismatic joints must be attached to
/// fixed bodies (which must be body1 on those joints).
class b2GearJoint : public b2Joint
{
public:
	b2Vec2 GetAnchorA() const;
	b2Vec2 GetAnchorB() const;

	b2Vec2 GetReactionForce(float32 inv_dt) const;
	float32 GetReactionTorque(float32 inv_dt) const;

	/// Set/Get the gear ratio.
	void SetRatio(float32 ratio);
	float32 GetRatio() const;

public:

	friend class b2Joint;
	b2GearJoint(const b2GearJointDef* data);

	void InitVelocityConstraints(const b2TimeStep& step);
	void SolveVelocityConstraints(const b2TimeStep& step);
	bool SolvePositionConstraints(float32 baumgarte);

	b2Body* m_ground1;
	b2Body* m_ground2;

	// One of these is NULL.
	b2RevoluteJoint* m_revolute1;
	b2PrismaticJoint* m_prismatic1;

	// One of these is NULL.
	b2RevoluteJoint* m_revolute2;
	b2PrismaticJoint* m_prismatic2;

	b2Vec2 m_groundAnchor1;
	b2Vec2 m_groundAnchor2;

	b2Vec2 m_localAnchor1;
	b2Vec2 m_localAnchor2;

	b2Jacobian m_J;

	float32 m_constant;
	float32 m_ratio;

	// Effective mass
	float32 m_mass;

	// Impulse for accumulation/warm starting.
	float32 m_impulse;
};

#endif
