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_REVOLUTE_JOINT_H
20 #define B2_REVOLUTE_JOINT_H
21
22 #include <Box2D/Dynamics/Joints/b2Joint.h>
23
24 /// Revolute joint definition. This requires defining an
25 /// anchor point where the bodies are joined. The definition
26 /// uses local anchor points so that the initial configuration
27 /// can violate the constraint slightly. You also need to
28 /// specify the initial relative angle for joint limits. This
29 /// helps when saving and loading a game.
30 /// The local anchor points are measured from the body's origin
31 /// rather than the center of mass because:
32 /// 1. you might not know where the center of mass will be.
33 /// 2. if you add/remove shapes from a body and recompute the mass,
34 /// the joints will be broken.
35 struct b2RevoluteJointDef : public b2JointDef
36 {
b2RevoluteJointDefb2RevoluteJointDef37 b2RevoluteJointDef()
38 {
39 type = e_revoluteJoint;
40 localAnchorA.Set(0.0f, 0.0f);
41 localAnchorB.Set(0.0f, 0.0f);
42 referenceAngle = 0.0f;
43 lowerAngle = 0.0f;
44 upperAngle = 0.0f;
45 maxMotorTorque = 0.0f;
46 motorSpeed = 0.0f;
47 enableLimit = false;
48 enableMotor = false;
49 }
50
51 /// Initialize the bodies, anchors, and reference angle using a world
52 /// anchor point.
53 void Initialize(b2Body* bodyA, b2Body* bodyB, const b2Vec2& anchor);
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 bodyB angle minus bodyA angle in the reference state (radians).
62 float32 referenceAngle;
63
64 /// A flag to enable joint limits.
65 bool enableLimit;
66
67 /// The lower angle for the joint limit (radians).
68 float32 lowerAngle;
69
70 /// The upper angle for the joint limit (radians).
71 float32 upperAngle;
72
73 /// A flag to enable the joint motor.
74 bool enableMotor;
75
76 /// The desired motor speed. Usually in radians per second.
77 float32 motorSpeed;
78
79 /// The maximum motor torque used to achieve the desired motor speed.
80 /// Usually in N-m.
81 float32 maxMotorTorque;
82 };
83
84 /// A revolute joint constrains two bodies to share a common point while they
85 /// are free to rotate about the point. The relative rotation about the shared
86 /// point is the joint angle. You can limit the relative rotation with
87 /// a joint limit that specifies a lower and upper angle. You can use a motor
88 /// to drive the relative rotation about the shared point. A maximum motor torque
89 /// is provided so that infinite forces are not generated.
90 class b2RevoluteJoint : public b2Joint
91 {
92 public:
93 b2Vec2 GetAnchorA() const;
94 b2Vec2 GetAnchorB() const;
95
96 /// The local anchor point relative to bodyA's origin.
GetLocalAnchorA()97 const b2Vec2& GetLocalAnchorA() const { return m_localAnchorA; }
98
99 /// The local anchor point relative to bodyB's origin.
GetLocalAnchorB()100 const b2Vec2& GetLocalAnchorB() const { return m_localAnchorB; }
101
102 /// Get the reference angle.
GetReferenceAngle()103 float32 GetReferenceAngle() const { return m_referenceAngle; }
104
105 /// Get the current joint angle in radians.
106 float32 GetJointAngle() const;
107
108 /// Get the current joint angle speed in radians per second.
109 float32 GetJointSpeed() const;
110
111 /// Is the joint limit enabled?
112 bool IsLimitEnabled() const;
113
114 /// Enable/disable the joint limit.
115 void EnableLimit(bool flag);
116
117 /// Get the lower joint limit in radians.
118 float32 GetLowerLimit() const;
119
120 /// Get the upper joint limit in radians.
121 float32 GetUpperLimit() const;
122
123 /// Set the joint limits in radians.
124 void SetLimits(float32 lower, float32 upper);
125
126 /// Is the joint motor enabled?
127 bool IsMotorEnabled() const;
128
129 /// Enable/disable the joint motor.
130 void EnableMotor(bool flag);
131
132 /// Set the motor speed in radians per second.
133 void SetMotorSpeed(float32 speed);
134
135 /// Get the motor speed in radians per second.
136 float32 GetMotorSpeed() const;
137
138 /// Set the maximum motor torque, usually in N-m.
139 void SetMaxMotorTorque(float32 torque);
GetMaxMotorTorque()140 float32 GetMaxMotorTorque() const { return m_maxMotorTorque; }
141
142 /// Get the reaction force given the inverse time step.
143 /// Unit is N.
144 b2Vec2 GetReactionForce(float32 inv_dt) const;
145
146 /// Get the reaction torque due to the joint limit given the inverse time step.
147 /// Unit is N*m.
148 float32 GetReactionTorque(float32 inv_dt) const;
149
150 /// Get the current motor torque given the inverse time step.
151 /// Unit is N*m.
152 float32 GetMotorTorque(float32 inv_dt) const;
153
154 /// Dump to b2Log.
155 void Dump();
156
157 protected:
158
159 friend class b2Joint;
160 friend class b2GearJoint;
161
162 b2RevoluteJoint(const b2RevoluteJointDef* def);
163
164 void InitVelocityConstraints(const b2SolverData& data);
165 void SolveVelocityConstraints(const b2SolverData& data);
166 bool SolvePositionConstraints(const b2SolverData& data);
167
168 // Solver shared
169 b2Vec2 m_localAnchorA;
170 b2Vec2 m_localAnchorB;
171 b2Vec3 m_impulse;
172 float32 m_motorImpulse;
173
174 bool m_enableMotor;
175 float32 m_maxMotorTorque;
176 float32 m_motorSpeed;
177
178 bool m_enableLimit;
179 float32 m_referenceAngle;
180 float32 m_lowerAngle;
181 float32 m_upperAngle;
182
183 // Solver temp
184 int32 m_indexA;
185 int32 m_indexB;
186 b2Vec2 m_rA;
187 b2Vec2 m_rB;
188 b2Vec2 m_localCenterA;
189 b2Vec2 m_localCenterB;
190 float32 m_invMassA;
191 float32 m_invMassB;
192 float32 m_invIA;
193 float32 m_invIB;
194 b2Mat33 m_mass; // effective mass for point-to-point constraint.
195 float32 m_motorMass; // effective mass for motor/limit angular constraint.
196 b2LimitState m_limitState;
197 };
198
GetMotorSpeed()199 inline float32 b2RevoluteJoint::GetMotorSpeed() const
200 {
201 return m_motorSpeed;
202 }
203
204 #endif
205