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_PULLEY_JOINT_H
20#define B2_PULLEY_JOINT_H
21
22#include <Box2D/Dynamics/Joints/b2Joint.h>
23
24const float32 b2_minPulleyLength = 2.0f;
25
26/// Pulley joint definition. This requires two ground anchors,
27/// two dynamic body anchor points, and a pulley ratio.
28struct b2PulleyJointDef : public b2JointDef
29{
30 b2PulleyJointDef()
31 {
32 type = e_pulleyJoint;
33 groundAnchorA.Set(-1.0f, 1.0f);
34 groundAnchorB.Set(1.0f, 1.0f);
35 localAnchorA.Set(-1.0f, 0.0f);
36 localAnchorB.Set(1.0f, 0.0f);
37 lengthA = 0.0f;
38 lengthB = 0.0f;
39 ratio = 1.0f;
40 collideConnected = true;
41 }
42
43 /// Initialize the bodies, anchors, lengths, max lengths, and ratio using the world anchors.
44 void Initialize(b2Body* bodyA, b2Body* bodyB,
45 const b2Vec2& groundAnchorA, const b2Vec2& groundAnchorB,
46 const b2Vec2& anchorA, const b2Vec2& anchorB,
47 float32 ratio);
48
49 /// The first ground anchor in world coordinates. This point never moves.
50 b2Vec2 groundAnchorA;
51
52 /// The second ground anchor in world coordinates. This point never moves.
53 b2Vec2 groundAnchorB;
54
55 /// The local anchor point relative to bodyA's origin.
56 b2Vec2 localAnchorA;
57
58 /// The local anchor point relative to bodyB's origin.
59 b2Vec2 localAnchorB;
60
61 /// The a reference length for the segment attached to bodyA.
62 float32 lengthA;
63
64 /// The a reference length for the segment attached to bodyB.
65 float32 lengthB;
66
67 /// The pulley ratio, used to simulate a block-and-tackle.
68 float32 ratio;
69};
70
71/// The pulley joint is connected to two bodies and two fixed ground points.
72/// The pulley supports a ratio such that:
73/// length1 + ratio * length2 <= constant
74/// Yes, the force transmitted is scaled by the ratio.
75/// Warning: the pulley joint can get a bit squirrelly by itself. They often
76/// work better when combined with prismatic joints. You should also cover the
77/// the anchor points with static shapes to prevent one side from going to
78/// zero length.
79class b2PulleyJoint : public b2Joint
80{
81public:
82 b2Vec2 GetAnchorA() const;
83 b2Vec2 GetAnchorB() const;
84
85 b2Vec2 GetReactionForce(float32 inv_dt) const;
86 float32 GetReactionTorque(float32 inv_dt) const;
87
88 /// Get the first ground anchor.
89 b2Vec2 GetGroundAnchorA() const;
90
91 /// Get the second ground anchor.
92 b2Vec2 GetGroundAnchorB() const;
93
94 /// Get the current length of the segment attached to bodyA.
95 float32 GetLengthA() const;
96
97 /// Get the current length of the segment attached to bodyB.
98 float32 GetLengthB() const;
99
100 /// Get the pulley ratio.
101 float32 GetRatio() const;
102
103 /// Get the current length of the segment attached to bodyA.
104 float32 GetCurrentLengthA() const;
105
106 /// Get the current length of the segment attached to bodyB.
107 float32 GetCurrentLengthB() const;
108
109 /// Dump joint to dmLog
110 void Dump();
111
112 /// Implement b2Joint::ShiftOrigin
113 void ShiftOrigin(const b2Vec2& newOrigin);
114
115protected:
116
117 friend class b2Joint;
118 b2PulleyJoint(const b2PulleyJointDef* data);
119
120 void InitVelocityConstraints(const b2SolverData& data);
121 void SolveVelocityConstraints(const b2SolverData& data);
122 bool SolvePositionConstraints(const b2SolverData& data);
123
124 b2Vec2 m_groundAnchorA;
125 b2Vec2 m_groundAnchorB;
126 float32 m_lengthA;
127 float32 m_lengthB;
128
129 // Solver shared
130 b2Vec2 m_localAnchorA;
131 b2Vec2 m_localAnchorB;
132 float32 m_constant;
133 float32 m_ratio;
134 float32 m_impulse;
135
136 // Solver temp
137 int32 m_indexA;
138 int32 m_indexB;
139 b2Vec2 m_uA;
140 b2Vec2 m_uB;
141 b2Vec2 m_rA;
142 b2Vec2 m_rB;
143 b2Vec2 m_localCenterA;
144 b2Vec2 m_localCenterB;
145 float32 m_invMassA;
146 float32 m_invMassB;
147 float32 m_invIA;
148 float32 m_invIB;
149 float32 m_mass;
150};
151
152#endif
153