1 /*
2 * Copyright (c) 2006-2007 Erin Catto http://www.box2d.org
3 *
4 * This software is provided 'as-is', without any express or implied
5 * warranty.  In no event will the authors be held liable for any damages
6 * arising from the use of this software.
7 * Permission is granted to anyone to use this software for any purpose,
8 * including commercial applications, and to alter it and redistribute it
9 * freely, subject to the following restrictions:
10 * 1. The origin of this software must not be misrepresented; you must not
11 * claim that you wrote the original software. If you use this software
12 * in a product, an acknowledgment in the product documentation would be
13 * appreciated but is not required.
14 * 2. Altered source versions must be plainly marked as such, and must not be
15 * misrepresented as being the original software.
16 * 3. This notice may not be removed or altered from any source distribution.
17 */
18 
19 #ifndef B2_FRICTION_JOINT_H
20 #define B2_FRICTION_JOINT_H
21 
22 #include <Box2D/Dynamics/Joints/b2Joint.h>
23 
24 /// Friction joint definition.
25 struct b2FrictionJointDef : public b2JointDef
26 {
b2FrictionJointDefb2FrictionJointDef27 	b2FrictionJointDef()
28 	{
29 		type = e_frictionJoint;
30 		localAnchorA.SetZero();
31 		localAnchorB.SetZero();
32 		maxForce = 0.0f;
33 		maxTorque = 0.0f;
34 	}
35 
36 	/// Initialize the bodies, anchors, axis, and reference angle using the world
37 	/// anchor and world axis.
38 	void Initialize(b2Body* bodyA, b2Body* bodyB, const b2Vec2& anchor);
39 
40 	/// The local anchor point relative to bodyA's origin.
41 	b2Vec2 localAnchorA;
42 
43 	/// The local anchor point relative to bodyB's origin.
44 	b2Vec2 localAnchorB;
45 
46 	/// The maximum friction force in N.
47 	float32 maxForce;
48 
49 	/// The maximum friction torque in N-m.
50 	float32 maxTorque;
51 };
52 
53 /// Friction joint. This is used for top-down friction.
54 /// It provides 2D translational friction and angular friction.
55 class b2FrictionJoint : public b2Joint
56 {
57 public:
58 	b2Vec2 GetAnchorA() const;
59 	b2Vec2 GetAnchorB() const;
60 
61 	b2Vec2 GetReactionForce(float32 inv_dt) const;
62 	float32 GetReactionTorque(float32 inv_dt) const;
63 
64 	/// The local anchor point relative to bodyA's origin.
GetLocalAnchorA()65 	const b2Vec2& GetLocalAnchorA() const { return m_localAnchorA; }
66 
67 	/// The local anchor point relative to bodyB's origin.
GetLocalAnchorB()68 	const b2Vec2& GetLocalAnchorB() const  { return m_localAnchorB; }
69 
70 	/// Set the maximum friction force in N.
71 	void SetMaxForce(float32 force);
72 
73 	/// Get the maximum friction force in N.
74 	float32 GetMaxForce() const;
75 
76 	/// Set the maximum friction torque in N*m.
77 	void SetMaxTorque(float32 torque);
78 
79 	/// Get the maximum friction torque in N*m.
80 	float32 GetMaxTorque() const;
81 
82 	/// Dump joint to dmLog
83 	void Dump();
84 
85 protected:
86 
87 	friend class b2Joint;
88 
89 	b2FrictionJoint(const b2FrictionJointDef* def);
90 
91 	void InitVelocityConstraints(const b2SolverData& data);
92 	void SolveVelocityConstraints(const b2SolverData& data);
93 	bool SolvePositionConstraints(const b2SolverData& data);
94 
95 	b2Vec2 m_localAnchorA;
96 	b2Vec2 m_localAnchorB;
97 
98 	// Solver shared
99 	b2Vec2 m_linearImpulse;
100 	float32 m_angularImpulse;
101 	float32 m_maxForce;
102 	float32 m_maxTorque;
103 
104 	// Solver temp
105 	int32 m_indexA;
106 	int32 m_indexB;
107 	b2Vec2 m_rA;
108 	b2Vec2 m_rB;
109 	b2Vec2 m_localCenterA;
110 	b2Vec2 m_localCenterB;
111 	float32 m_invMassA;
112 	float32 m_invMassB;
113 	float32 m_invIA;
114 	float32 m_invIB;
115 	b2Mat22 m_linearMass;
116 	float32 m_angularMass;
117 };
118 
119 #endif
120