1/*
2* Copyright (c) 2006-2011 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_ROPE_JOINT_H
20#define B2_ROPE_JOINT_H
21
22#include <Box2D/Dynamics/Joints/b2Joint.h>
23
24/// Rope joint definition. This requires two body anchor points and
25/// a maximum lengths.
26/// Note: by default the connected objects will not collide.
27/// see collideConnected in b2JointDef.
28struct b2RopeJointDef : public b2JointDef
29{
30 b2RopeJointDef()
31 {
32 type = e_ropeJoint;
33 localAnchorA.Set(-1.0f, 0.0f);
34 localAnchorB.Set(1.0f, 0.0f);
35 maxLength = 0.0f;
36 }
37
38 /// The local anchor point relative to bodyA's origin.
39 b2Vec2 localAnchorA;
40
41 /// The local anchor point relative to bodyB's origin.
42 b2Vec2 localAnchorB;
43
44 /// The maximum length of the rope.
45 /// Warning: this must be larger than b2_linearSlop or
46 /// the joint will have no effect.
47 float32 maxLength;
48};
49
50/// A rope joint enforces a maximum distance between two points
51/// on two bodies. It has no other effect.
52/// Warning: if you attempt to change the maximum length during
53/// the simulation you will get some non-physical behavior.
54/// A model that would allow you to dynamically modify the length
55/// would have some sponginess, so I chose not to implement it
56/// that way. See b2DistanceJoint if you want to dynamically
57/// control length.
58class b2RopeJoint : public b2Joint
59{
60public:
61 b2Vec2 GetAnchorA() const;
62 b2Vec2 GetAnchorB() const;
63
64 b2Vec2 GetReactionForce(float32 inv_dt) const;
65 float32 GetReactionTorque(float32 inv_dt) const;
66
67 /// The local anchor point relative to bodyA's origin.
68 const b2Vec2& GetLocalAnchorA() const { return m_localAnchorA; }
69
70 /// The local anchor point relative to bodyB's origin.
71 const b2Vec2& GetLocalAnchorB() const { return m_localAnchorB; }
72
73 /// Set/Get the maximum length of the rope.
74 void SetMaxLength(float32 length) { m_maxLength = length; }
75 float32 GetMaxLength() const;
76
77 b2LimitState GetLimitState() const;
78
79 /// Dump joint to dmLog
80 void Dump();
81
82protected:
83
84 friend class b2Joint;
85 b2RopeJoint(const b2RopeJointDef* data);
86
87 void InitVelocityConstraints(const b2SolverData& data);
88 void SolveVelocityConstraints(const b2SolverData& data);
89 bool SolvePositionConstraints(const b2SolverData& data);
90
91 // Solver shared
92 b2Vec2 m_localAnchorA;
93 b2Vec2 m_localAnchorB;
94 float32 m_maxLength;
95 float32 m_length;
96 float32 m_impulse;
97
98 // Solver temp
99 int32 m_indexA;
100 int32 m_indexB;
101 b2Vec2 m_u;
102 b2Vec2 m_rA;
103 b2Vec2 m_rB;
104 b2Vec2 m_localCenterA;
105 b2Vec2 m_localCenterB;
106 float32 m_invMassA;
107 float32 m_invMassB;
108 float32 m_invIA;
109 float32 m_invIB;
110 float32 m_mass;
111 b2LimitState m_state;
112};
113
114#endif
115