b2DistanceJoint.cpp
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1 /*
2 * Copyright (c) 2006-2011 Erin Catto http://www.box2d.org
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18 
20 #include <Box2D/Dynamics/b2Body.h>
22 
23 // 1-D constrained system
24 // m (v2 - v1) = lambda
25 // v2 + (beta/h) * x1 + gamma * lambda = 0, gamma has units of inverse mass.
26 // x2 = x1 + h * v2
27 
28 // 1-D mass-damper-spring system
29 // m (v2 - v1) + h * d * v2 + h * k *
30 
31 // C = norm(p2 - p1) - L
32 // u = (p2 - p1) / norm(p2 - p1)
33 // Cdot = dot(u, v2 + cross(w2, r2) - v1 - cross(w1, r1))
34 // J = [-u -cross(r1, u) u cross(r2, u)]
35 // K = J * invM * JT
36 // = invMass1 + invI1 * cross(r1, u)^2 + invMass2 + invI2 * cross(r2, u)^2
37 
39  const b2Vec2& anchor1, const b2Vec2& anchor2)
40 {
41  bodyA = b1;
42  bodyB = b2;
43  localAnchorA = bodyA->GetLocalPoint(anchor1);
44  localAnchorB = bodyB->GetLocalPoint(anchor2);
45  b2Vec2 d = anchor2 - anchor1;
46  length = d.Length();
47 }
48 
50 : b2Joint(def)
51 {
54  m_length = def->length;
57  m_impulse = 0.0f;
58  m_gamma = 0.0f;
59  m_bias = 0.0f;
60 }
61 
63 {
72 
73  b2Vec2 cA = data.positions[m_indexA].c;
74  float32 aA = data.positions[m_indexA].a;
75  b2Vec2 vA = data.velocities[m_indexA].v;
76  float32 wA = data.velocities[m_indexA].w;
77 
78  b2Vec2 cB = data.positions[m_indexB].c;
79  float32 aB = data.positions[m_indexB].a;
80  b2Vec2 vB = data.velocities[m_indexB].v;
81  float32 wB = data.velocities[m_indexB].w;
82 
83  b2Rot qA(aA), qB(aB);
84 
87  m_u = cB + m_rB - cA - m_rA;
88 
89  // Handle singularity.
91  if (length > b2_linearSlop)
92  {
93  m_u *= 1.0f / length;
94  }
95  else
96  {
97  m_u.Set(0.0f, 0.0f);
98  }
99 
100  float32 crAu = b2Cross(m_rA, m_u);
101  float32 crBu = b2Cross(m_rB, m_u);
102  float32 invMass = m_invMassA + m_invIA * crAu * crAu + m_invMassB + m_invIB * crBu * crBu;
103 
104  // Compute the effective mass matrix.
105  m_mass = invMass != 0.0f ? 1.0f / invMass : 0.0f;
106 
107  if (m_frequencyHz > 0.0f)
108  {
109  float32 C = length - m_length;
110 
111  // Frequency
112  float32 omega = 2.0f * b2_pi * m_frequencyHz;
113 
114  // Damping coefficient
115  float32 d = 2.0f * m_mass * m_dampingRatio * omega;
116 
117  // Spring stiffness
118  float32 k = m_mass * omega * omega;
119 
120  // magic formulas
121  float32 h = data.step.dt;
122  m_gamma = h * (d + h * k);
123  m_gamma = m_gamma != 0.0f ? 1.0f / m_gamma : 0.0f;
124  m_bias = C * h * k * m_gamma;
125 
126  invMass += m_gamma;
127  m_mass = invMass != 0.0f ? 1.0f / invMass : 0.0f;
128  }
129  else
130  {
131  m_gamma = 0.0f;
132  m_bias = 0.0f;
133  }
134 
135  if (data.step.warmStarting)
136  {
137  // Scale the impulse to support a variable time step.
138  m_impulse *= data.step.dtRatio;
139 
140  b2Vec2 P = m_impulse * m_u;
141  vA -= m_invMassA * P;
142  wA -= m_invIA * b2Cross(m_rA, P);
143  vB += m_invMassB * P;
144  wB += m_invIB * b2Cross(m_rB, P);
145  }
146  else
147  {
148  m_impulse = 0.0f;
149  }
150 
151  data.velocities[m_indexA].v = vA;
152  data.velocities[m_indexA].w = wA;
153  data.velocities[m_indexB].v = vB;
154  data.velocities[m_indexB].w = wB;
155 }
156 
158 {
159  b2Vec2 vA = data.velocities[m_indexA].v;
160  float32 wA = data.velocities[m_indexA].w;
161  b2Vec2 vB = data.velocities[m_indexB].v;
162  float32 wB = data.velocities[m_indexB].w;
163 
164  // Cdot = dot(u, v + cross(w, r))
165  b2Vec2 vpA = vA + b2Cross(wA, m_rA);
166  b2Vec2 vpB = vB + b2Cross(wB, m_rB);
167  float32 Cdot = b2Dot(m_u, vpB - vpA);
168 
169  float32 impulse = -m_mass * (Cdot + m_bias + m_gamma * m_impulse);
170  m_impulse += impulse;
171 
172  b2Vec2 P = impulse * m_u;
173  vA -= m_invMassA * P;
174  wA -= m_invIA * b2Cross(m_rA, P);
175  vB += m_invMassB * P;
176  wB += m_invIB * b2Cross(m_rB, P);
177 
178  data.velocities[m_indexA].v = vA;
179  data.velocities[m_indexA].w = wA;
180  data.velocities[m_indexB].v = vB;
181  data.velocities[m_indexB].w = wB;
182 }
183 
185 {
186  if (m_frequencyHz > 0.0f)
187  {
188  // There is no position correction for soft distance constraints.
189  return true;
190  }
191 
192  b2Vec2 cA = data.positions[m_indexA].c;
193  float32 aA = data.positions[m_indexA].a;
194  b2Vec2 cB = data.positions[m_indexB].c;
195  float32 aB = data.positions[m_indexB].a;
196 
197  b2Rot qA(aA), qB(aB);
198 
201  b2Vec2 u = cB + rB - cA - rA;
202 
203  float32 length = u.Normalize();
204  float32 C = length - m_length;
206 
207  float32 impulse = -m_mass * C;
208  b2Vec2 P = impulse * u;
209 
210  cA -= m_invMassA * P;
211  aA -= m_invIA * b2Cross(rA, P);
212  cB += m_invMassB * P;
213  aB += m_invIB * b2Cross(rB, P);
214 
215  data.positions[m_indexA].c = cA;
216  data.positions[m_indexA].a = aA;
217  data.positions[m_indexB].c = cB;
218  data.positions[m_indexB].a = aB;
219 
220  return b2Abs(C) < b2_linearSlop;
221 }
222 
224 {
226 }
227 
229 {
231 }
232 
234 {
235  b2Vec2 F = (inv_dt * m_impulse) * m_u;
236  return F;
237 }
238 
240 {
241  B2_NOT_USED(inv_dt);
242  return 0.0f;
243 }
244 
246 {
247  int32 indexA = m_bodyA->m_islandIndex;
248  int32 indexB = m_bodyB->m_islandIndex;
249 
250  b2Log(" b2DistanceJointDef jd;\n");
251  b2Log(" jd.bodyA = bodies[%d];\n", indexA);
252  b2Log(" jd.bodyB = bodies[%d];\n", indexB);
253  b2Log(" jd.collideConnected = bool(%d);\n", m_collideConnected);
254  b2Log(" jd.localAnchorA.Set(%.15lef, %.15lef);\n", m_localAnchorA.x, m_localAnchorA.y);
255  b2Log(" jd.localAnchorB.Set(%.15lef, %.15lef);\n", m_localAnchorB.x, m_localAnchorB.y);
256  b2Log(" jd.length = %.15lef;\n", m_length);
257  b2Log(" jd.frequencyHz = %.15lef;\n", m_frequencyHz);
258  b2Log(" jd.dampingRatio = %.15lef;\n", m_dampingRatio);
259  b2Log(" joints[%d] = m_world->CreateJoint(&jd);\n", m_index);
260 }
d
GLuint GLsizei GLsizei * length
float32 b2Dot(const b2Vec2 &a, const b2Vec2 &b)
Perform the dot product on two vectors.
Definition: b2Math.h:405
b2Velocity * velocities
Definition: b2TimeStep.h:67
float32 m_invMass
Definition: b2Body.h:455
int32 m_islandIndex
Definition: b2Body.h:434
b2Vec2 b2Mul(const b2Mat22 &A, const b2Vec2 &v)
Definition: b2Math.h:432
void b2Log(const char *string,...)
Logging function.
Definition: b2Settings.cpp:38
float32 a
Definition: b2TimeStep.h:52
#define b2_linearSlop
Definition: b2Settings.h:68
#define b2_pi
Definition: b2Settings.h:40
b2TimeStep step
Definition: b2TimeStep.h:65
void Dump()
Dump joint to dmLog.
void SolveVelocityConstraints(const b2SolverData &data)
b2Vec2 c
Definition: b2TimeStep.h:51
float32 w
Definition: b2TimeStep.h:59
bool m_collideConnected
Definition: b2Joint.h:181
#define B2_NOT_USED(x)
Definition: b2Settings.h:26
float32 dtRatio
Definition: b2TimeStep.h:42
b2Vec2 GetWorldPoint(const b2Vec2 &localPoint) const
Definition: b2Body.h:556
Solver Data.
Definition: b2TimeStep.h:63
int32 m_index
Definition: b2Joint.h:178
A 2D column vector.
Definition: b2Math.h:52
#define b2_maxLinearCorrection
Definition: b2Settings.h:94
signed int int32
Definition: b2Settings.h:31
b2Vec2 localCenter
local center of mass position
Definition: b2Math.h:392
float32 b2Cross(const b2Vec2 &a, const b2Vec2 &b)
Perform the cross product on two vectors. In 2D this produces a scalar.
Definition: b2Math.h:411
A rigid body. These are created via b2World::CreateBody.
Definition: b2Body.h:126
float32 dampingRatio
The damping ratio. 0 = no damping, 1 = critical damping.
b2Vec2 v
Definition: b2TimeStep.h:58
void Initialize(b2Body *bodyA, b2Body *bodyB, const b2Vec2 &anchorA, const b2Vec2 &anchorB)
float32 m_invI
Definition: b2Body.h:458
GLint GLenum GLsizei GLint GLsizei const GLvoid * data
float32 GetReactionTorque(float32 inv_dt) const
b2Vec2 localAnchorA
The local anchor point relative to bodyA&#39;s origin.
b2Body * m_bodyA
Definition: b2Joint.h:175
b2Vec2 localAnchorB
The local anchor point relative to bodyB&#39;s origin.
b2Vec2 GetAnchorA() const
Get the anchor point on bodyA in world coordinates.
float32 y
Definition: b2Math.h:139
b2Vec2 GetLocalPoint(const b2Vec2 &worldPoint) const
Definition: b2Body.h:566
b2Position * positions
Definition: b2TimeStep.h:66
T b2Clamp(T a, T low, T high)
Definition: b2Math.h:653
bool SolvePositionConstraints(const b2SolverData &data)
T b2Abs(T a)
Definition: b2Math.h:615
bool warmStarting
Definition: b2TimeStep.h:45
Rotation.
Definition: b2Math.h:298
b2Vec2 GetReactionForce(float32 inv_dt) const
float32 x
Definition: b2Math.h:139
b2Body * bodyA
The first attached body.
Definition: b2Joint.h:92
float32 Normalize()
Convert this vector into a unit vector. Returns the length.
Definition: b2Math.h:113
void Set(float32 x_, float32 y_)
Set this vector to some specified coordinates.
Definition: b2Math.h:64
float32 dt
Definition: b2TimeStep.h:40
float32 Length() const
Get the length of this vector (the norm).
Definition: b2Math.h:100
float32 length
The natural length between the anchor points.
b2Body * bodyB
The second attached body.
Definition: b2Joint.h:95
b2Body * m_bodyB
Definition: b2Joint.h:176
b2DistanceJoint(const b2DistanceJointDef *data)
b2Sweep m_sweep
Definition: b2Body.h:437
float float32
Definition: b2Settings.h:35
void InitVelocityConstraints(const b2SolverData &data)
CArrayDouble< 6 > C
GLdouble GLdouble GLdouble GLdouble GLdouble GLdouble f
b2Vec2 GetAnchorB() const
Get the anchor point on bodyB in world coordinates.


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autogenerated on Fri May 7 2021 03:05:51