axmol/Box2D/Dynamics/Joints/b2Joint.h

/*
* 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_JOINT_H
#define B2_JOINT_H

#include <Box2D/Common/b2Math.h>

class b2Body;
class b2Joint;
struct b2TimeStep;
class b2BlockAllocator;

enum b2JointType
{
	e_unknownJoint,
	e_revoluteJoint,
	e_prismaticJoint,
	e_distanceJoint,
	e_pulleyJoint,
	e_mouseJoint,
	e_gearJoint,
	e_lineJoint,
    e_weldJoint,
	e_frictionJoint,
};

enum b2LimitState
{
	e_inactiveLimit,
	e_atLowerLimit,
	e_atUpperLimit,
	e_equalLimits
};

struct b2Jacobian
{
	b2Vec2 linearA;
	float32 angularA;
	b2Vec2 linearB;
	float32 angularB;

	void SetZero();
	void Set(const b2Vec2& x1, float32 a1, const b2Vec2& x2, float32 a2);
	float32 Compute(const b2Vec2& x1, float32 a1, const b2Vec2& x2, float32 a2);
};

/// A joint edge is used to connect bodies and joints together
/// in a joint graph where each body is a node and each joint
/// is an edge. A joint edge belongs to a doubly linked list
/// maintained in each attached body. Each joint has two joint
/// nodes, one for each attached body.
struct b2JointEdge
{
	b2Body* other;			///< provides quick access to the other body attached.
	b2Joint* joint;			///< the joint
	b2JointEdge* prev;		///< the previous joint edge in the body's joint list
	b2JointEdge* next;		///< the next joint edge in the body's joint list
};

/// Joint definitions are used to construct joints.
struct b2JointDef
{
	b2JointDef()
	{
		type = e_unknownJoint;
		userData = NULL;
		bodyA = NULL;
		bodyB = NULL;
		collideConnected = false;
	}

	/// The joint type is set automatically for concrete joint types.
	b2JointType type;

	/// Use this to attach application specific data to your joints.
	void* userData;

	/// The first attached body.
	b2Body* bodyA;

	/// The second attached body.
	b2Body* bodyB;

	/// Set this flag to true if the attached bodies should collide.
	bool collideConnected;
};

/// The base joint class. Joints are used to constraint two bodies together in
/// various fashions. Some joints also feature limits and motors.
class b2Joint
{
public:

	/// Get the type of the concrete joint.
	b2JointType GetType() const;

	/// Get the first body attached to this joint.
	b2Body* GetBodyA();

	/// Get the second body attached to this joint.
	b2Body* GetBodyB();

	/// Get the anchor point on bodyA in world coordinates.
	virtual b2Vec2 GetAnchorA() const = 0;

	/// Get the anchor point on bodyB in world coordinates.
	virtual b2Vec2 GetAnchorB() const = 0;

	/// Get the reaction force on body2 at the joint anchor in Newtons.
	virtual b2Vec2 GetReactionForce(float32 inv_dt) const = 0;

	/// Get the reaction torque on body2 in N*m.
	virtual float32 GetReactionTorque(float32 inv_dt) const = 0;

	/// Get the next joint the world joint list.
	b2Joint* GetNext();

	/// Get the user data pointer.
	void* GetUserData() const;

	/// Set the user data pointer.
	void SetUserData(void* data);

	/// Short-cut function to determine if either body is inactive.
	bool IsActive() const;

protected:
	friend class b2World;
	friend class b2Body;
	friend class b2Island;

	static b2Joint* Create(const b2JointDef* def, b2BlockAllocator* allocator);
	static void Destroy(b2Joint* joint, b2BlockAllocator* allocator);

	b2Joint(const b2JointDef* def);
	virtual ~b2Joint() {}

	virtual void InitVelocityConstraints(const b2TimeStep& step) = 0;
	virtual void SolveVelocityConstraints(const b2TimeStep& step) = 0;

	// This returns true if the position errors are within tolerance.
	virtual bool SolvePositionConstraints(float32 baumgarte) = 0;

	b2JointType m_type;
	b2Joint* m_prev;
	b2Joint* m_next;
	b2JointEdge m_edgeA;
	b2JointEdge m_edgeB;
	b2Body* m_bodyA;
	b2Body* m_bodyB;

	bool m_islandFlag;
	bool m_collideConnected;

	void* m_userData;

	// Cache here per time step to reduce cache misses.
	b2Vec2 m_localCenterA, m_localCenterB;
	float32 m_invMassA, m_invIA;
	float32 m_invMassB, m_invIB;
};

inline void b2Jacobian::SetZero()
{
	linearA.SetZero(); angularA = 0.0f;
	linearB.SetZero(); angularB = 0.0f;
}

inline void b2Jacobian::Set(const b2Vec2& x1, float32 a1, const b2Vec2& x2, float32 a2)
{
	linearA = x1; angularA = a1;
	linearB = x2; angularB = a2;
}

inline float32 b2Jacobian::Compute(const b2Vec2& x1, float32 a1, const b2Vec2& x2, float32 a2)
{
	return b2Dot(linearA, x1) + angularA * a1 + b2Dot(linearB, x2) + angularB * a2;
}

inline b2JointType b2Joint::GetType() const
{
	return m_type;
}

inline b2Body* b2Joint::GetBodyA()
{
	return m_bodyA;
}

inline b2Body* b2Joint::GetBodyB()
{
	return m_bodyB;
}

inline b2Joint* b2Joint::GetNext()
{
	return m_next;
}

inline void* b2Joint::GetUserData() const
{
	return m_userData;
}

inline void b2Joint::SetUserData(void* data)
{
	m_userData = data;
}

#endif