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_DISTANCE_JOINT_H
20 #define B2_DISTANCE_JOINT_H
21
22 #include <Box2D/Dynamics/Joints/b2Joint.h>
23
24 /// Distance joint definition. This requires defining an
25 /// anchor point on both bodies and the non-zero length of the
26 /// distance joint. The definition uses local anchor points
27 /// so that the initial configuration can violate the constraint
28 /// slightly. This helps when saving and loading a game.
29 /// @warning Do not use a zero or short length.
30 struct b2DistanceJointDef : public b2JointDef
31 {
b2DistanceJointDefb2DistanceJointDef32 b2DistanceJointDef()
33 {
34 type = e_distanceJoint;
35 localAnchorA.Set(0.0f, 0.0f);
36 localAnchorB.Set(0.0f, 0.0f);
37 length = 1.0f;
38 frequencyHz = 0.0f;
39 dampingRatio = 0.0f;
40 }
41
42 /// Initialize the bodies, anchors, and length using the world
43 /// anchors.
44 void Initialize(b2Body* bodyA, b2Body* bodyB,
45 const b2Vec2& anchorA, const b2Vec2& anchorB);
46
47 /// The local anchor point relative to bodyA's origin.
48 b2Vec2 localAnchorA;
49
50 /// The local anchor point relative to bodyB's origin.
51 b2Vec2 localAnchorB;
52
53 /// The natural length between the anchor points.
54 float32 length;
55
56 /// The mass-spring-damper frequency in Hertz. A value of 0
57 /// disables softness.
58 float32 frequencyHz;
59
60 /// The damping ratio. 0 = no damping, 1 = critical damping.
61 float32 dampingRatio;
62 };
63
64 /// A distance joint constrains two points on two bodies
65 /// to remain at a fixed distance from each other. You can view
66 /// this as a massless, rigid rod.
67 class b2DistanceJoint : public b2Joint
68 {
69 public:
70
71 b2Vec2 GetAnchorA() const;
72 b2Vec2 GetAnchorB() const;
73
74 /// Get the reaction force given the inverse time step.
75 /// Unit is N.
76 b2Vec2 GetReactionForce(float32 inv_dt) const;
77
78 /// Get the reaction torque given the inverse time step.
79 /// Unit is N*m. This is always zero for a distance joint.
80 float32 GetReactionTorque(float32 inv_dt) const;
81
82 /// The local anchor point relative to bodyA's origin.
GetLocalAnchorA()83 const b2Vec2& GetLocalAnchorA() const { return m_localAnchorA; }
84
85 /// The local anchor point relative to bodyB's origin.
GetLocalAnchorB()86 const b2Vec2& GetLocalAnchorB() const { return m_localAnchorB; }
87
88 /// Set/get the natural length.
89 /// Manipulating the length can lead to non-physical behavior when the frequency is zero.
90 void SetLength(float32 length);
91 float32 GetLength() const;
92
93 /// Set/get frequency in Hz.
94 void SetFrequency(float32 hz);
95 float32 GetFrequency() const;
96
97 /// Set/get damping ratio.
98 void SetDampingRatio(float32 ratio);
99 float32 GetDampingRatio() const;
100
101 /// Dump joint to dmLog
102 void Dump();
103
104 protected:
105
106 friend class b2Joint;
107 b2DistanceJoint(const b2DistanceJointDef* data);
108
109 void InitVelocityConstraints(const b2SolverData& data);
110 void SolveVelocityConstraints(const b2SolverData& data);
111 bool SolvePositionConstraints(const b2SolverData& data);
112
113 float32 m_frequencyHz;
114 float32 m_dampingRatio;
115 float32 m_bias;
116
117 // Solver shared
118 b2Vec2 m_localAnchorA;
119 b2Vec2 m_localAnchorB;
120 float32 m_gamma;
121 float32 m_impulse;
122 float32 m_length;
123
124 // Solver temp
125 int32 m_indexA;
126 int32 m_indexB;
127 b2Vec2 m_u;
128 b2Vec2 m_rA;
129 b2Vec2 m_rB;
130 b2Vec2 m_localCenterA;
131 b2Vec2 m_localCenterB;
132 float32 m_invMassA;
133 float32 m_invMassB;
134 float32 m_invIA;
135 float32 m_invIB;
136 float32 m_mass;
137 };
138
SetLength(float32 length)139 inline void b2DistanceJoint::SetLength(float32 length)
140 {
141 m_length = length;
142 }
143
GetLength()144 inline float32 b2DistanceJoint::GetLength() const
145 {
146 return m_length;
147 }
148
SetFrequency(float32 hz)149 inline void b2DistanceJoint::SetFrequency(float32 hz)
150 {
151 m_frequencyHz = hz;
152 }
153
GetFrequency()154 inline float32 b2DistanceJoint::GetFrequency() const
155 {
156 return m_frequencyHz;
157 }
158
SetDampingRatio(float32 ratio)159 inline void b2DistanceJoint::SetDampingRatio(float32 ratio)
160 {
161 m_dampingRatio = ratio;
162 }
163
GetDampingRatio()164 inline float32 b2DistanceJoint::GetDampingRatio() const
165 {
166 return m_dampingRatio;
167 }
168
169 #endif
170