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_PRISMATIC_JOINT_H
20#define B2_PRISMATIC_JOINT_H
21
22#include <Box2D/Dynamics/Joints/b2Joint.h>
23
24/// Prismatic 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.
30struct b2PrismaticJointDef : public b2JointDef
31{
32 b2PrismaticJointDef()
33 {
34 type = e_prismaticJoint;
35 localAnchorA.SetZero();
36 localAnchorB.SetZero();
37 localAxisA.Set(1.0f, 0.0f);
38 referenceAngle = 0.0f;
39 enableLimit = false;
40 lowerTranslation = 0.0f;
41 upperTranslation = 0.0f;
42 enableMotor = false;
43 maxMotorForce = 0.0f;
44 motorSpeed = 0.0f;
45 }
46
47 /// Initialize the bodies, anchors, axis, and reference angle using the world
48 /// anchor and unit world axis.
49 void Initialize(b2Body* bodyA, b2Body* bodyB, const b2Vec2& anchor, const b2Vec2& axis);
50
51 /// The local anchor point relative to bodyA's origin.
52 b2Vec2 localAnchorA;
53
54 /// The local anchor point relative to bodyB's origin.
55 b2Vec2 localAnchorB;
56
57 /// The local translation unit axis in bodyA.
58 b2Vec2 localAxisA;
59
60 /// The constrained angle between the bodies: bodyB_angle - bodyA_angle.
61 float32 referenceAngle;
62
63 /// Enable/disable the joint limit.
64 bool enableLimit;
65
66 /// The lower translation limit, usually in meters.
67 float32 lowerTranslation;
68
69 /// The upper translation limit, usually in meters.
70 float32 upperTranslation;
71
72 /// Enable/disable the joint motor.
73 bool enableMotor;
74
75 /// The maximum motor torque, usually in N-m.
76 float32 maxMotorForce;
77
78 /// The desired motor speed in radians per second.
79 float32 motorSpeed;
80};
81
82/// A prismatic joint. This joint provides one degree of freedom: translation
83/// along an axis fixed in bodyA. Relative rotation is prevented. You can
84/// use a joint limit to restrict the range of motion and a joint motor to
85/// drive the motion or to model joint friction.
86class b2PrismaticJoint : public b2Joint
87{
88public:
89 b2Vec2 GetAnchorA() const;
90 b2Vec2 GetAnchorB() const;
91
92 b2Vec2 GetReactionForce(float32 inv_dt) const;
93 float32 GetReactionTorque(float32 inv_dt) const;
94
95 /// The local anchor point relative to bodyA's origin.
96 const b2Vec2& GetLocalAnchorA() const { return m_localAnchorA; }
97
98 /// The local anchor point relative to bodyB's origin.
99 const b2Vec2& GetLocalAnchorB() const { return m_localAnchorB; }
100
101 /// The local joint axis relative to bodyA.
102 const b2Vec2& GetLocalAxisA() const { return m_localXAxisA; }
103
104 /// Get the reference angle.
105 float32 GetReferenceAngle() const { return m_referenceAngle; }
106
107 /// Get the current joint translation, usually in meters.
108 float32 GetJointTranslation() const;
109
110 /// Get the current joint translation speed, usually in meters per second.
111 float32 GetJointSpeed() const;
112
113 /// Is the joint limit enabled?
114 bool IsLimitEnabled() const;
115
116 /// Enable/disable the joint limit.
117 void EnableLimit(bool flag);
118
119 /// Get the lower joint limit, usually in meters.
120 float32 GetLowerLimit() const;
121
122 /// Get the upper joint limit, usually in meters.
123 float32 GetUpperLimit() const;
124
125 /// Set the joint limits, usually in meters.
126 void SetLimits(float32 lower, float32 upper);
127
128 /// Is the joint motor enabled?
129 bool IsMotorEnabled() const;
130
131 /// Enable/disable the joint motor.
132 void EnableMotor(bool flag);
133
134 /// Set the motor speed, usually in meters per second.
135 void SetMotorSpeed(float32 speed);
136
137 /// Get the motor speed, usually in meters per second.
138 float32 GetMotorSpeed() const;
139
140 /// Set the maximum motor force, usually in N.
141 void SetMaxMotorForce(float32 force);
142 float32 GetMaxMotorForce() const { return m_maxMotorForce; }
143
144 /// Get the current motor force given the inverse time step, usually in N.
145 float32 GetMotorForce(float32 inv_dt) const;
146
147 /// Dump to b2Log
148 void Dump();
149
150protected:
151 friend class b2Joint;
152 friend class b2GearJoint;
153 b2PrismaticJoint(const b2PrismaticJointDef* def);
154
155 void InitVelocityConstraints(const b2SolverData& data);
156 void SolveVelocityConstraints(const b2SolverData& data);
157 bool SolvePositionConstraints(const b2SolverData& data);
158
159 // Solver shared
160 b2Vec2 m_localAnchorA;
161 b2Vec2 m_localAnchorB;
162 b2Vec2 m_localXAxisA;
163 b2Vec2 m_localYAxisA;
164 float32 m_referenceAngle;
165 b2Vec3 m_impulse;
166 float32 m_motorImpulse;
167 float32 m_lowerTranslation;
168 float32 m_upperTranslation;
169 float32 m_maxMotorForce;
170 float32 m_motorSpeed;
171 bool m_enableLimit;
172 bool m_enableMotor;
173 b2LimitState m_limitState;
174
175 // Solver temp
176 int32 m_indexA;
177 int32 m_indexB;
178 b2Vec2 m_localCenterA;
179 b2Vec2 m_localCenterB;
180 float32 m_invMassA;
181 float32 m_invMassB;
182 float32 m_invIA;
183 float32 m_invIB;
184 b2Vec2 m_axis, m_perp;
185 float32 m_s1, m_s2;
186 float32 m_a1, m_a2;
187 b2Mat33 m_K;
188 float32 m_motorMass;
189};
190
191inline float32 b2PrismaticJoint::GetMotorSpeed() const
192{
193 return m_motorSpeed;
194}
195
196#endif
197