1 /*
2 * Copyright (c) 2006-2007 Erin Catto http://www.gphysics.com
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_JOINT_H
20 #define B2_JOINT_H
21
22 #include <Box2D/Common/b2Math.h>
23
24 class b2Body;
25 class b2Joint;
26 struct b2TimeStep;
27 class b2BlockAllocator;
28
29 enum b2JointType
30 {
31 e_unknownJoint,
32 e_revoluteJoint,
33 e_prismaticJoint,
34 e_distanceJoint,
35 e_pulleyJoint,
36 e_mouseJoint,
37 e_gearJoint,
38 e_lineJoint,
39 e_weldJoint,
40 e_frictionJoint,
41 e_ropeJoint
42 };
43
44 enum b2LimitState
45 {
46 e_inactiveLimit,
47 e_atLowerLimit,
48 e_atUpperLimit,
49 e_equalLimits
50 };
51
52 struct b2Jacobian
53 {
54 b2Vec2 linearA;
55 qreal angularA;
56 b2Vec2 linearB;
57 qreal angularB;
58
59 void SetZero();
60 void Set(const b2Vec2& x1, qreal a1, const b2Vec2& x2, qreal a2);
61 qreal Compute(const b2Vec2& x1, qreal a1, const b2Vec2& x2, qreal a2);
62 };
63
64 /// A joint edge is used to connect bodies and joints together
65 /// in a joint graph where each body is a node and each joint
66 /// is an edge. A joint edge belongs to a doubly linked list
67 /// maintained in each attached body. Each joint has two joint
68 /// nodes, one for each attached body.
69 struct b2JointEdge
70 {
71 b2Body* other; ///< provides quick access to the other body attached.
72 b2Joint* joint; ///< the joint
73 b2JointEdge* prev; ///< the previous joint edge in the body's joint list
74 b2JointEdge* next; ///< the next joint edge in the body's joint list
75 };
76
77 /// Joint definitions are used to construct joints.
78 struct b2JointDef
79 {
b2JointDefb2JointDef80 b2JointDef()
81 {
82 type = e_unknownJoint;
83 userData = NULL;
84 bodyA = NULL;
85 bodyB = NULL;
86 collideConnected = false;
87 }
88
89 /// The joint type is set automatically for concrete joint types.
90 b2JointType type;
91
92 /// Use this to attach application specific data to your joints.
93 void* userData;
94
95 /// The first attached body.
96 b2Body* bodyA;
97
98 /// The second attached body.
99 b2Body* bodyB;
100
101 /// Set this flag to true if the attached bodies should collide.
102 bool collideConnected;
103 };
104
105 /// The base joint class. Joints are used to constraint two bodies together in
106 /// various fashions. Some joints also feature limits and motors.
107 class b2Joint
108 {
109 public:
110
111 /// Get the type of the concrete joint.
112 b2JointType GetType() const;
113
114 /// Get the first body attached to this joint.
115 b2Body* GetBodyA();
116
117 /// Get the second body attached to this joint.
118 b2Body* GetBodyB();
119
120 /// Get the anchor point on bodyA in world coordinates.
121 virtual b2Vec2 GetAnchorA() const = 0;
122
123 /// Get the anchor point on bodyB in world coordinates.
124 virtual b2Vec2 GetAnchorB() const = 0;
125
126 /// Get the reaction force on body2 at the joint anchor in Newtons.
127 virtual b2Vec2 GetReactionForce(qreal inv_dt) const = 0;
128
129 /// Get the reaction torque on body2 in N*m.
130 virtual qreal GetReactionTorque(qreal inv_dt) const = 0;
131
132 /// Get the next joint the world joint list.
133 b2Joint* GetNext();
134 const b2Joint* GetNext() const;
135
136 /// Get the user data pointer.
137 void* GetUserData() const;
138
139 /// Set the user data pointer.
140 void SetUserData(void* data);
141
142 /// Short-cut function to determine if either body is inactive.
143 bool IsActive() const;
144
145 protected:
146 friend class b2World;
147 friend class b2Body;
148 friend class b2Island;
149
150 static b2Joint* Create(const b2JointDef* def, b2BlockAllocator* allocator);
151 static void Destroy(b2Joint* joint, b2BlockAllocator* allocator);
152
153 b2Joint(const b2JointDef* def);
~b2Joint()154 virtual ~b2Joint() {}
155
156 virtual void InitVelocityConstraints(const b2TimeStep& step) = 0;
157 virtual void SolveVelocityConstraints(const b2TimeStep& step) = 0;
158
159 // This returns true if the position errors are within tolerance.
160 virtual bool SolvePositionConstraints(qreal baumgarte) = 0;
161
162 b2JointType m_type;
163 b2Joint* m_prev;
164 b2Joint* m_next;
165 b2JointEdge m_edgeA;
166 b2JointEdge m_edgeB;
167 b2Body* m_bodyA;
168 b2Body* m_bodyB;
169
170 bool m_islandFlag;
171 bool m_collideConnected;
172
173 void* m_userData;
174
175 // Cache here per time step to reduce cache misses.
176 // TODO_ERIN will be wrong if the mass changes.
177 b2Vec2 m_localCenterA, m_localCenterB;
178 qreal m_invMassA, m_invIA;
179 qreal m_invMassB, m_invIB;
180 };
181
SetZero()182 inline void b2Jacobian::SetZero()
183 {
184 linearA.SetZero(); angularA = 0.0f;
185 linearB.SetZero(); angularB = 0.0f;
186 }
187
Set(const b2Vec2 & x1,qreal a1,const b2Vec2 & x2,qreal a2)188 inline void b2Jacobian::Set(const b2Vec2& x1, qreal a1, const b2Vec2& x2, qreal a2)
189 {
190 linearA = x1; angularA = a1;
191 linearB = x2; angularB = a2;
192 }
193
Compute(const b2Vec2 & x1,qreal a1,const b2Vec2 & x2,qreal a2)194 inline qreal b2Jacobian::Compute(const b2Vec2& x1, qreal a1, const b2Vec2& x2, qreal a2)
195 {
196 return b2Dot(linearA, x1) + angularA * a1 + b2Dot(linearB, x2) + angularB * a2;
197 }
198
GetType()199 inline b2JointType b2Joint::GetType() const
200 {
201 return m_type;
202 }
203
GetBodyA()204 inline b2Body* b2Joint::GetBodyA()
205 {
206 return m_bodyA;
207 }
208
GetBodyB()209 inline b2Body* b2Joint::GetBodyB()
210 {
211 return m_bodyB;
212 }
213
GetNext()214 inline b2Joint* b2Joint::GetNext()
215 {
216 return m_next;
217 }
218
GetNext()219 inline const b2Joint* b2Joint::GetNext() const
220 {
221 return m_next;
222 }
223
GetUserData()224 inline void* b2Joint::GetUserData() const
225 {
226 return m_userData;
227 }
228
SetUserData(void * data)229 inline void b2Joint::SetUserData(void* data)
230 {
231 m_userData = data;
232 }
233
234 #endif
235