/*
* Copyright (c) 2006-2009 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_WELD_JOINT_H
#define B2_WELD_JOINT_H

#include <Box2D/Dynamics/Joints/b2Joint.h>

/// Weld joint definition. You need to specify local anchor points
/// where they are attached and the relative body angle. The position
/// of the anchor points is important for computing the reaction torque.
struct b2WeldJointDef : public b2JointDef
{
	b2WeldJointDef()
	{
		type = e_weldJoint;
		localAnchorA.Set(0.0f, 0.0f);
		localAnchorB.Set(0.0f, 0.0f);
		referenceAngle = 0.0f;
	}

	/// Initialize the bodies, anchors, and reference angle using a world
	/// anchor point.
	void Initialize(b2Body* body1, b2Body* body2, const b2Vec2& anchor);

	/// The local anchor point relative to body1's origin.
	b2Vec2 localAnchorA;

	/// The local anchor point relative to body2's origin.
	b2Vec2 localAnchorB;

	/// The body2 angle minus body1 angle in the reference state (radians).
	float32 referenceAngle;
};

/// A weld joint essentially glues two bodies together. A weld joint may
/// distort somewhat because the island constraint solver is approximate.
class b2WeldJoint : public b2Joint
{
public:
	b2Vec2 GetAnchorA() const;
	b2Vec2 GetAnchorB() const;

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

protected:

	friend class b2Joint;

	b2WeldJoint(const b2WeldJointDef* def);

	void InitVelocityConstraints(const b2TimeStep& step);
	void SolveVelocityConstraints(const b2TimeStep& step);

	bool SolvePositionConstraints(float32 baumgarte);

	b2Vec2 m_localAnchorA;
	b2Vec2 m_localAnchorB;
	float32 m_referenceAngle;

	b2Vec3 m_impulse;

	b2Mat33 m_mass;
};

#endif

