Box2D  2.4.1
A 2D physics engine for games
b2_pulley_joint.h
1 // MIT License
2 
3 // Copyright (c) 2019 Erin Catto
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22 
23 #ifndef B2_PULLEY_JOINT_H
24 #define B2_PULLEY_JOINT_H
25 
26 #include "b2_api.h"
27 #include "b2_joint.h"
28 
29 const float b2_minPulleyLength = 2.0f;
30 
33 struct B2_API b2PulleyJointDef : public b2JointDef
34 {
36  {
37  type = e_pulleyJoint;
38  groundAnchorA.Set(-1.0f, 1.0f);
39  groundAnchorB.Set(1.0f, 1.0f);
40  localAnchorA.Set(-1.0f, 0.0f);
41  localAnchorB.Set(1.0f, 0.0f);
42  lengthA = 0.0f;
43  lengthB = 0.0f;
44  ratio = 1.0f;
45  collideConnected = true;
46  }
47 
49  void Initialize(b2Body* bodyA, b2Body* bodyB,
50  const b2Vec2& groundAnchorA, const b2Vec2& groundAnchorB,
51  const b2Vec2& anchorA, const b2Vec2& anchorB,
52  float ratio);
53 
56 
59 
62 
65 
67  float lengthA;
68 
70  float lengthB;
71 
73  float ratio;
74 };
75 
84 class B2_API b2PulleyJoint : public b2Joint
85 {
86 public:
87  b2Vec2 GetAnchorA() const override;
88  b2Vec2 GetAnchorB() const override;
89 
90  b2Vec2 GetReactionForce(float inv_dt) const override;
91  float GetReactionTorque(float inv_dt) const override;
92 
95 
98 
100  float GetLengthA() const;
101 
103  float GetLengthB() const;
104 
106  float GetRatio() const;
107 
109  float GetCurrentLengthA() const;
110 
112  float GetCurrentLengthB() const;
113 
115  void Dump() override;
116 
118  void ShiftOrigin(const b2Vec2& newOrigin) override;
119 
120 protected:
121 
122  friend class b2Joint;
123  b2PulleyJoint(const b2PulleyJointDef* data);
124 
125  void InitVelocityConstraints(const b2SolverData& data) override;
126  void SolveVelocityConstraints(const b2SolverData& data) override;
127  bool SolvePositionConstraints(const b2SolverData& data) override;
128 
129  b2Vec2 m_groundAnchorA;
130  b2Vec2 m_groundAnchorB;
131  float m_lengthA;
132  float m_lengthB;
133 
134  // Solver shared
135  b2Vec2 m_localAnchorA;
136  b2Vec2 m_localAnchorB;
137  float m_constant;
138  float m_ratio;
139  float m_impulse;
140 
141  // Solver temp
142  int32 m_indexA;
143  int32 m_indexB;
144  b2Vec2 m_uA;
145  b2Vec2 m_uB;
146  b2Vec2 m_rA;
147  b2Vec2 m_rB;
148  b2Vec2 m_localCenterA;
149  b2Vec2 m_localCenterB;
150  float m_invMassA;
151  float m_invMassB;
152  float m_invIA;
153  float m_invIB;
154  float m_mass;
155 };
156 
157 #endif
A rigid body. These are created via b2World::CreateBody.
Definition: b2_body.h:129
Definition: b2_joint.h:111
Definition: b2_pulley_joint.h:85
b2Vec2 GetGroundAnchorA() const
Get the first ground anchor.
float GetLengthB() const
Get the current length of the segment attached to bodyB.
float GetRatio() const
Get the pulley ratio.
void Dump() override
Dump joint to dmLog.
void ShiftOrigin(const b2Vec2 &newOrigin) override
Implement b2Joint::ShiftOrigin.
b2Vec2 GetReactionForce(float inv_dt) const override
Get the reaction force on bodyB at the joint anchor in Newtons.
float GetReactionTorque(float inv_dt) const override
Get the reaction torque on bodyB in N*m.
float GetCurrentLengthB() const
Get the current length of the segment attached to bodyB.
float GetLengthA() const
Get the current length of the segment attached to bodyA.
b2Vec2 GetAnchorB() const override
Get the anchor point on bodyB in world coordinates.
float GetCurrentLengthA() const
Get the current length of the segment attached to bodyA.
b2Vec2 GetAnchorA() const override
Get the anchor point on bodyA in world coordinates.
b2Vec2 GetGroundAnchorB() const
Get the second ground anchor.
Joint definitions are used to construct joints.
Definition: b2_joint.h:73
Definition: b2_pulley_joint.h:34
float ratio
The pulley ratio, used to simulate a block-and-tackle.
Definition: b2_pulley_joint.h:73
float lengthA
The a reference length for the segment attached to bodyA.
Definition: b2_pulley_joint.h:67
float lengthB
The a reference length for the segment attached to bodyB.
Definition: b2_pulley_joint.h:70
b2Vec2 groundAnchorB
The second ground anchor in world coordinates. This point never moves.
Definition: b2_pulley_joint.h:58
b2Vec2 groundAnchorA
The first ground anchor in world coordinates. This point never moves.
Definition: b2_pulley_joint.h:55
b2Vec2 localAnchorA
The local anchor point relative to bodyA's origin.
Definition: b2_pulley_joint.h:61
void Initialize(b2Body *bodyA, b2Body *bodyB, const b2Vec2 &groundAnchorA, const b2Vec2 &groundAnchorB, const b2Vec2 &anchorA, const b2Vec2 &anchorB, float ratio)
Initialize the bodies, anchors, lengths, max lengths, and ratio using the world anchors.
b2Vec2 localAnchorB
The local anchor point relative to bodyB's origin.
Definition: b2_pulley_joint.h:64
Solver Data.
Definition: b2_time_step.h:68
A 2D column vector.
Definition: b2_math.h:42