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_WHEEL_JOINT_H
20 #define B2_WHEEL_JOINT_H
21
22 #include <Box2D/Dynamics/Joints/b2Joint.h>
23
24 /// Wheel joint definition. This requires defining a line of
25 /// motion using an axis and an anchor point. The definition uses local
26 /// anchor points and a local axis so that the initial configuration
27 /// can violate the constraint slightly. The joint translation is zero
28 /// when the local anchor points coincide in world space. Using local
29 /// anchors and a local axis helps when saving and loading a game.
30 struct b2WheelJointDef : public b2JointDef
31 {
b2WheelJointDefb2WheelJointDef32 b2WheelJointDef()
33 {
34 type = e_wheelJoint;
35 localAnchorA.SetZero();
36 localAnchorB.SetZero();
37 localAxisA.Set(1.0f, 0.0f);
38 enableMotor = false;
39 maxMotorTorque = 0.0f;
40 motorSpeed = 0.0f;
41 frequencyHz = 2.0f;
42 dampingRatio = 0.7f;
43 }
44
45 /// Initialize the bodies, anchors, axis, and reference angle using the world
46 /// anchor and world axis.
47 void Initialize(b2Body* bodyA, b2Body* bodyB, const b2Vec2& anchor, const b2Vec2& axis);
48
49 /// The local anchor point relative to bodyA's origin.
50 b2Vec2 localAnchorA;
51
52 /// The local anchor point relative to bodyB's origin.
53 b2Vec2 localAnchorB;
54
55 /// The local translation axis in bodyA.
56 b2Vec2 localAxisA;
57
58 /// Enable/disable the joint motor.
59 bool enableMotor;
60
61 /// The maximum motor torque, usually in N-m.
62 float32 maxMotorTorque;
63
64 /// The desired motor speed in radians per second.
65 float32 motorSpeed;
66
67 /// Suspension frequency, zero indicates no suspension
68 float32 frequencyHz;
69
70 /// Suspension damping ratio, one indicates critical damping
71 float32 dampingRatio;
72 };
73
74 /// A wheel joint. This joint provides two degrees of freedom: translation
75 /// along an axis fixed in bodyA and rotation in the plane. In other words, it is a point to
76 /// line constraint with a rotational motor and a linear spring/damper.
77 /// This joint is designed for vehicle suspensions.
78 class b2WheelJoint : public b2Joint
79 {
80 public:
81 b2Vec2 GetAnchorA() const;
82 b2Vec2 GetAnchorB() const;
83
84 b2Vec2 GetReactionForce(float32 inv_dt) const;
85 float32 GetReactionTorque(float32 inv_dt) const;
86
87 /// The local anchor point relative to bodyA's origin.
GetLocalAnchorA()88 const b2Vec2& GetLocalAnchorA() const { return m_localAnchorA; }
89
90 /// The local anchor point relative to bodyB's origin.
GetLocalAnchorB()91 const b2Vec2& GetLocalAnchorB() const { return m_localAnchorB; }
92
93 /// The local joint axis relative to bodyA.
GetLocalAxisA()94 const b2Vec2& GetLocalAxisA() const { return m_localXAxisA; }
95
96 /// Get the current joint translation, usually in meters.
97 float32 GetJointTranslation() const;
98
99 /// Get the current joint linear speed, usually in meters per second.
100 float32 GetJointLinearSpeed() const;
101
102 /// Get the current joint angle in radians.
103 float32 GetJointAngle() const;
104
105 /// Get the current joint angular speed in radians per second.
106 float32 GetJointAngularSpeed() const;
107
108 /// Is the joint motor enabled?
109 bool IsMotorEnabled() const;
110
111 /// Enable/disable the joint motor.
112 void EnableMotor(bool flag);
113
114 /// Set the motor speed, usually in radians per second.
115 void SetMotorSpeed(float32 speed);
116
117 /// Get the motor speed, usually in radians per second.
118 float32 GetMotorSpeed() const;
119
120 /// Set/Get the maximum motor force, usually in N-m.
121 void SetMaxMotorTorque(float32 torque);
122 float32 GetMaxMotorTorque() const;
123
124 /// Get the current motor torque given the inverse time step, usually in N-m.
125 float32 GetMotorTorque(float32 inv_dt) const;
126
127 /// Set/Get the spring frequency in hertz. Setting the frequency to zero disables the spring.
128 void SetSpringFrequencyHz(float32 hz);
129 float32 GetSpringFrequencyHz() const;
130
131 /// Set/Get the spring damping ratio
132 void SetSpringDampingRatio(float32 ratio);
133 float32 GetSpringDampingRatio() const;
134
135 /// Dump to b2Log
136 void Dump();
137
138 protected:
139
140 friend class b2Joint;
141 b2WheelJoint(const b2WheelJointDef* def);
142
143 void InitVelocityConstraints(const b2SolverData& data);
144 void SolveVelocityConstraints(const b2SolverData& data);
145 bool SolvePositionConstraints(const b2SolverData& data);
146
147 float32 m_frequencyHz;
148 float32 m_dampingRatio;
149
150 // Solver shared
151 b2Vec2 m_localAnchorA;
152 b2Vec2 m_localAnchorB;
153 b2Vec2 m_localXAxisA;
154 b2Vec2 m_localYAxisA;
155
156 float32 m_impulse;
157 float32 m_motorImpulse;
158 float32 m_springImpulse;
159
160 float32 m_maxMotorTorque;
161 float32 m_motorSpeed;
162 bool m_enableMotor;
163
164 // Solver temp
165 int32 m_indexA;
166 int32 m_indexB;
167 b2Vec2 m_localCenterA;
168 b2Vec2 m_localCenterB;
169 float32 m_invMassA;
170 float32 m_invMassB;
171 float32 m_invIA;
172 float32 m_invIB;
173
174 b2Vec2 m_ax, m_ay;
175 float32 m_sAx, m_sBx;
176 float32 m_sAy, m_sBy;
177
178 float32 m_mass;
179 float32 m_motorMass;
180 float32 m_springMass;
181
182 float32 m_bias;
183 float32 m_gamma;
184 };
185
GetMotorSpeed()186 inline float32 b2WheelJoint::GetMotorSpeed() const
187 {
188 return m_motorSpeed;
189 }
190
GetMaxMotorTorque()191 inline float32 b2WheelJoint::GetMaxMotorTorque() const
192 {
193 return m_maxMotorTorque;
194 }
195
SetSpringFrequencyHz(float32 hz)196 inline void b2WheelJoint::SetSpringFrequencyHz(float32 hz)
197 {
198 m_frequencyHz = hz;
199 }
200
GetSpringFrequencyHz()201 inline float32 b2WheelJoint::GetSpringFrequencyHz() const
202 {
203 return m_frequencyHz;
204 }
205
SetSpringDampingRatio(float32 ratio)206 inline void b2WheelJoint::SetSpringDampingRatio(float32 ratio)
207 {
208 m_dampingRatio = ratio;
209 }
210
GetSpringDampingRatio()211 inline float32 b2WheelJoint::GetSpringDampingRatio() const
212 {
213 return m_dampingRatio;
214 }
215
216 #endif
217