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.
35struct b2RevoluteJointDef : public b2JointDef
36{
37	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.
90class b2RevoluteJoint : public b2Joint
91{
92public:
93	b2Vec2 GetAnchorA() const;
94	b2Vec2 GetAnchorB() const;
95
96	/// The local anchor point relative to bodyA's origin.
97	const b2Vec2& GetLocalAnchorA() const { return m_localAnchorA; }
98
99	/// The local anchor point relative to bodyB's origin.
100	const b2Vec2& GetLocalAnchorB() const  { return m_localAnchorB; }
101
102	/// Get the reference angle.
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);
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
157protected:
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
199inline float32 b2RevoluteJoint::GetMotorSpeed() const
200{
201	return m_motorSpeed;
202}
203
204#endif
205