b2RevoluteJoint.cpp
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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
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17 */
18 
20 #include <Box2D/Dynamics/b2Body.h>
22 
23 // Point-to-point constraint
24 // C = p2 - p1
25 // Cdot = v2 - v1
26 // = v2 + cross(w2, r2) - v1 - cross(w1, r1)
27 // J = [-I -r1_skew I r2_skew ]
28 // Identity used:
29 // w k % (rx i + ry j) = w * (-ry i + rx j)
30 
31 // Motor constraint
32 // Cdot = w2 - w1
33 // J = [0 0 -1 0 0 1]
34 // K = invI1 + invI2
35 
36 void b2RevoluteJointDef::Initialize(b2Body* bA, b2Body* bB, const b2Vec2& anchor)
37 {
38  bodyA = bA;
39  bodyB = bB;
40  localAnchorA = bodyA->GetLocalPoint(anchor);
41  localAnchorB = bodyB->GetLocalPoint(anchor);
43 }
44 
46 : b2Joint(def)
47 {
51 
53  m_motorImpulse = 0.0f;
54 
55  m_lowerAngle = def->lowerAngle;
56  m_upperAngle = def->upperAngle;
58  m_motorSpeed = def->motorSpeed;
62 }
63 
65 {
74 
75  float32 aA = data.positions[m_indexA].a;
76  b2Vec2 vA = data.velocities[m_indexA].v;
77  float32 wA = data.velocities[m_indexA].w;
78 
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 
88  // J = [-I -r1_skew I r2_skew]
89  // [ 0 -1 0 1]
90  // r_skew = [-ry; rx]
91 
92  // Matlab
93  // K = [ mA+r1y^2*iA+mB+r2y^2*iB, -r1y*iA*r1x-r2y*iB*r2x, -r1y*iA-r2y*iB]
94  // [ -r1y*iA*r1x-r2y*iB*r2x, mA+r1x^2*iA+mB+r2x^2*iB, r1x*iA+r2x*iB]
95  // [ -r1y*iA-r2y*iB, r1x*iA+r2x*iB, iA+iB]
96 
97  float32 mA = m_invMassA, mB = m_invMassB;
98  float32 iA = m_invIA, iB = m_invIB;
99 
100  bool fixedRotation = (iA + iB == 0.0f);
101 
102  m_mass.ex.x = mA + mB + m_rA.y * m_rA.y * iA + m_rB.y * m_rB.y * iB;
103  m_mass.ey.x = -m_rA.y * m_rA.x * iA - m_rB.y * m_rB.x * iB;
104  m_mass.ez.x = -m_rA.y * iA - m_rB.y * iB;
105  m_mass.ex.y = m_mass.ey.x;
106  m_mass.ey.y = mA + mB + m_rA.x * m_rA.x * iA + m_rB.x * m_rB.x * iB;
107  m_mass.ez.y = m_rA.x * iA + m_rB.x * iB;
108  m_mass.ex.z = m_mass.ez.x;
109  m_mass.ey.z = m_mass.ez.y;
110  m_mass.ez.z = iA + iB;
111 
112  m_motorMass = iA + iB;
113  if (m_motorMass > 0.0f)
114  {
115  m_motorMass = 1.0f / m_motorMass;
116  }
117 
118  if (m_enableMotor == false || fixedRotation)
119  {
120  m_motorImpulse = 0.0f;
121  }
122 
123  if (m_enableLimit && fixedRotation == false)
124  {
125  float32 jointAngle = aB - aA - m_referenceAngle;
127  {
129  }
130  else if (jointAngle <= m_lowerAngle)
131  {
133  {
134  m_impulse.z = 0.0f;
135  }
137  }
138  else if (jointAngle >= m_upperAngle)
139  {
141  {
142  m_impulse.z = 0.0f;
143  }
145  }
146  else
147  {
149  m_impulse.z = 0.0f;
150  }
151  }
152  else
153  {
155  }
156 
157  if (data.step.warmStarting)
158  {
159  // Scale impulses to support a variable time step.
160  m_impulse *= data.step.dtRatio;
161  m_motorImpulse *= data.step.dtRatio;
162 
164 
165  vA -= mA * P;
166  wA -= iA * (b2Cross(m_rA, P) + m_motorImpulse + m_impulse.z);
167 
168  vB += mB * P;
169  wB += iB * (b2Cross(m_rB, P) + m_motorImpulse + m_impulse.z);
170  }
171  else
172  {
173  m_impulse.SetZero();
174  m_motorImpulse = 0.0f;
175  }
176 
177  data.velocities[m_indexA].v = vA;
178  data.velocities[m_indexA].w = wA;
179  data.velocities[m_indexB].v = vB;
180  data.velocities[m_indexB].w = wB;
181 }
182 
184 {
185  b2Vec2 vA = data.velocities[m_indexA].v;
186  float32 wA = data.velocities[m_indexA].w;
187  b2Vec2 vB = data.velocities[m_indexB].v;
188  float32 wB = data.velocities[m_indexB].w;
189 
190  float32 mA = m_invMassA, mB = m_invMassB;
191  float32 iA = m_invIA, iB = m_invIB;
192 
193  bool fixedRotation = (iA + iB == 0.0f);
194 
195  // Solve motor constraint.
196  if (m_enableMotor && m_limitState != e_equalLimits && fixedRotation == false)
197  {
198  float32 Cdot = wB - wA - m_motorSpeed;
199  float32 impulse = -m_motorMass * Cdot;
200  float32 oldImpulse = m_motorImpulse;
201  float32 maxImpulse = data.step.dt * m_maxMotorTorque;
202  m_motorImpulse = b2Clamp(m_motorImpulse + impulse, -maxImpulse, maxImpulse);
203  impulse = m_motorImpulse - oldImpulse;
204 
205  wA -= iA * impulse;
206  wB += iB * impulse;
207  }
208 
209  // Solve limit constraint.
210  if (m_enableLimit && m_limitState != e_inactiveLimit && fixedRotation == false)
211  {
212  b2Vec2 Cdot1 = vB + b2Cross(wB, m_rB) - vA - b2Cross(wA, m_rA);
213  float32 Cdot2 = wB - wA;
214  b2Vec3 Cdot(Cdot1.x, Cdot1.y, Cdot2);
215 
216  b2Vec3 impulse = -m_mass.Solve33(Cdot);
217 
219  {
220  m_impulse += impulse;
221  }
222  else if (m_limitState == e_atLowerLimit)
223  {
224  float32 newImpulse = m_impulse.z + impulse.z;
225  if (newImpulse < 0.0f)
226  {
227  b2Vec2 rhs = -Cdot1 + m_impulse.z * b2Vec2(m_mass.ez.x, m_mass.ez.y);
228  b2Vec2 reduced = m_mass.Solve22(rhs);
229  impulse.x = reduced.x;
230  impulse.y = reduced.y;
231  impulse.z = -m_impulse.z;
232  m_impulse.x += reduced.x;
233  m_impulse.y += reduced.y;
234  m_impulse.z = 0.0f;
235  }
236  else
237  {
238  m_impulse += impulse;
239  }
240  }
241  else if (m_limitState == e_atUpperLimit)
242  {
243  float32 newImpulse = m_impulse.z + impulse.z;
244  if (newImpulse > 0.0f)
245  {
246  b2Vec2 rhs = -Cdot1 + m_impulse.z * b2Vec2(m_mass.ez.x, m_mass.ez.y);
247  b2Vec2 reduced = m_mass.Solve22(rhs);
248  impulse.x = reduced.x;
249  impulse.y = reduced.y;
250  impulse.z = -m_impulse.z;
251  m_impulse.x += reduced.x;
252  m_impulse.y += reduced.y;
253  m_impulse.z = 0.0f;
254  }
255  else
256  {
257  m_impulse += impulse;
258  }
259  }
260 
261  b2Vec2 P(impulse.x, impulse.y);
262 
263  vA -= mA * P;
264  wA -= iA * (b2Cross(m_rA, P) + impulse.z);
265 
266  vB += mB * P;
267  wB += iB * (b2Cross(m_rB, P) + impulse.z);
268  }
269  else
270  {
271  // Solve point-to-point constraint
272  b2Vec2 Cdot = vB + b2Cross(wB, m_rB) - vA - b2Cross(wA, m_rA);
273  b2Vec2 impulse = m_mass.Solve22(-Cdot);
274 
275  m_impulse.x += impulse.x;
276  m_impulse.y += impulse.y;
277 
278  vA -= mA * impulse;
279  wA -= iA * b2Cross(m_rA, impulse);
280 
281  vB += mB * impulse;
282  wB += iB * b2Cross(m_rB, impulse);
283  }
284 
285  data.velocities[m_indexA].v = vA;
286  data.velocities[m_indexA].w = wA;
287  data.velocities[m_indexB].v = vB;
288  data.velocities[m_indexB].w = wB;
289 }
290 
292 {
293  b2Vec2 cA = data.positions[m_indexA].c;
294  float32 aA = data.positions[m_indexA].a;
295  b2Vec2 cB = data.positions[m_indexB].c;
296  float32 aB = data.positions[m_indexB].a;
297 
298  b2Rot qA(aA), qB(aB);
299 
300  float32 angularError = 0.0f;
301  float32 positionError = 0.0f;
302 
303  bool fixedRotation = (m_invIA + m_invIB == 0.0f);
304 
305  // Solve angular limit constraint.
306  if (m_enableLimit && m_limitState != e_inactiveLimit && fixedRotation == false)
307  {
308  float32 angle = aB - aA - m_referenceAngle;
309  float32 limitImpulse = 0.0f;
310 
312  {
313  // Prevent large angular corrections
315  limitImpulse = -m_motorMass * C;
316  angularError = b2Abs(C);
317  }
318  else if (m_limitState == e_atLowerLimit)
319  {
320  float32 C = angle - m_lowerAngle;
321  angularError = -C;
322 
323  // Prevent large angular corrections and allow some slop.
325  limitImpulse = -m_motorMass * C;
326  }
327  else if (m_limitState == e_atUpperLimit)
328  {
329  float32 C = angle - m_upperAngle;
330  angularError = C;
331 
332  // Prevent large angular corrections and allow some slop.
334  limitImpulse = -m_motorMass * C;
335  }
336 
337  aA -= m_invIA * limitImpulse;
338  aB += m_invIB * limitImpulse;
339  }
340 
341  // Solve point-to-point constraint.
342  {
343  qA.Set(aA);
344  qB.Set(aB);
347 
348  b2Vec2 C = cB + rB - cA - rA;
349  positionError = C.Length();
350 
351  float32 mA = m_invMassA, mB = m_invMassB;
352  float32 iA = m_invIA, iB = m_invIB;
353 
354  b2Mat22 K;
355  K.ex.x = mA + mB + iA * rA.y * rA.y + iB * rB.y * rB.y;
356  K.ex.y = -iA * rA.x * rA.y - iB * rB.x * rB.y;
357  K.ey.x = K.ex.y;
358  K.ey.y = mA + mB + iA * rA.x * rA.x + iB * rB.x * rB.x;
359 
360  b2Vec2 impulse = -K.Solve(C);
361 
362  cA -= mA * impulse;
363  aA -= iA * b2Cross(rA, impulse);
364 
365  cB += mB * impulse;
366  aB += iB * b2Cross(rB, impulse);
367  }
368 
369  data.positions[m_indexA].c = cA;
370  data.positions[m_indexA].a = aA;
371  data.positions[m_indexB].c = cB;
372  data.positions[m_indexB].a = aB;
373 
374  return positionError <= b2_linearSlop && angularError <= b2_angularSlop;
375 }
376 
378 {
380 }
381 
383 {
385 }
386 
388 {
390  return inv_dt * P;
391 }
392 
394 {
395  return inv_dt * m_impulse.z;
396 }
397 
399 {
400  b2Body* bA = m_bodyA;
401  b2Body* bB = m_bodyB;
402  return bB->m_sweep.a - bA->m_sweep.a - m_referenceAngle;
403 }
404 
406 {
407  b2Body* bA = m_bodyA;
408  b2Body* bB = m_bodyB;
409  return bB->m_angularVelocity - bA->m_angularVelocity;
410 }
411 
413 {
414  return m_enableMotor;
415 }
416 
418 {
419  m_bodyA->SetAwake(true);
420  m_bodyB->SetAwake(true);
421  m_enableMotor = flag;
422 }
423 
425 {
426  return inv_dt * m_motorImpulse;
427 }
428 
430 {
431  m_bodyA->SetAwake(true);
432  m_bodyB->SetAwake(true);
433  m_motorSpeed = speed;
434 }
435 
437 {
438  m_bodyA->SetAwake(true);
439  m_bodyB->SetAwake(true);
440  m_maxMotorTorque = torque;
441 }
442 
444 {
445  return m_enableLimit;
446 }
447 
449 {
450  if (flag != m_enableLimit)
451  {
452  m_bodyA->SetAwake(true);
453  m_bodyB->SetAwake(true);
454  m_enableLimit = flag;
455  m_impulse.z = 0.0f;
456  }
457 }
458 
460 {
461  return m_lowerAngle;
462 }
463 
465 {
466  return m_upperAngle;
467 }
468 
470 {
471  b2Assert(lower <= upper);
472 
473  if (lower != m_lowerAngle || upper != m_upperAngle)
474  {
475  m_bodyA->SetAwake(true);
476  m_bodyB->SetAwake(true);
477  m_impulse.z = 0.0f;
478  m_lowerAngle = lower;
479  m_upperAngle = upper;
480  }
481 }
482 
484 {
485  int32 indexA = m_bodyA->m_islandIndex;
486  int32 indexB = m_bodyB->m_islandIndex;
487 
488  b2Log(" b2RevoluteJointDef jd;\n");
489  b2Log(" jd.bodyA = bodies[%d];\n", indexA);
490  b2Log(" jd.bodyB = bodies[%d];\n", indexB);
491  b2Log(" jd.collideConnected = bool(%d);\n", m_collideConnected);
492  b2Log(" jd.localAnchorA.Set(%.15lef, %.15lef);\n", m_localAnchorA.x, m_localAnchorA.y);
493  b2Log(" jd.localAnchorB.Set(%.15lef, %.15lef);\n", m_localAnchorB.x, m_localAnchorB.y);
494  b2Log(" jd.referenceAngle = %.15lef;\n", m_referenceAngle);
495  b2Log(" jd.enableLimit = bool(%d);\n", m_enableLimit);
496  b2Log(" jd.lowerAngle = %.15lef;\n", m_lowerAngle);
497  b2Log(" jd.upperAngle = %.15lef;\n", m_upperAngle);
498  b2Log(" jd.enableMotor = bool(%d);\n", m_enableMotor);
499  b2Log(" jd.motorSpeed = %.15lef;\n", m_motorSpeed);
500  b2Log(" jd.maxMotorTorque = %.15lef;\n", m_maxMotorTorque);
501  b2Log(" joints[%d] = m_world->CreateJoint(&jd);\n", m_index);
502 }
float32 upperAngle
The upper angle for the joint limit (radians).
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
b2Vec2 GetReactionForce(float32 inv_dt) const
void b2Log(const char *string,...)
Logging function.
Definition: b2Settings.cpp:38
b2Vec3 ex
Definition: b2Math.h:294
b2Vec2 localAnchorB
The local anchor point relative to bodyB&#39;s origin.
float32 a
Definition: b2TimeStep.h:52
#define b2_linearSlop
Definition: b2Settings.h:68
bool IsMotorEnabled() const
Is the joint motor enabled?
void Dump()
Dump to b2Log.
b2TimeStep step
Definition: b2TimeStep.h:65
void Initialize(b2Body *bodyA, b2Body *bodyB, const b2Vec2 &anchor)
b2Vec2 GetAnchorA() const
Get the anchor point on bodyA in world coordinates.
void InitVelocityConstraints(const b2SolverData &data)
float32 GetJointAngle() const
Get the current joint angle in radians.
b2Vec2 c
Definition: b2TimeStep.h:51
b2LimitState m_limitState
float32 w
Definition: b2TimeStep.h:59
b2Vec2 GetAnchorB() const
Get the anchor point on bodyB in world coordinates.
bool m_collideConnected
Definition: b2Joint.h:181
float32 dtRatio
Definition: b2TimeStep.h:42
float32 y
Definition: b2Math.h:178
void SolveVelocityConstraints(const b2SolverData &data)
#define b2_maxAngularCorrection
Definition: b2Settings.h:98
bool SolvePositionConstraints(const b2SolverData &data)
b2Vec2 GetWorldPoint(const b2Vec2 &localPoint) const
Definition: b2Body.h:556
float32 GetAngle() const
Definition: b2Body.h:484
b2Vec3 ez
Definition: b2Math.h:294
Solver Data.
Definition: b2TimeStep.h:63
void SetMaxMotorTorque(float32 torque)
Set the maximum motor torque, usually in N-m.
int32 m_index
Definition: b2Joint.h:178
A 2D column vector.
Definition: b2Math.h:52
b2Vec2 ey
Definition: b2Math.h:252
float32 m_referenceAngle
signed int int32
Definition: b2Settings.h:31
float32 motorSpeed
The desired motor speed. Usually in radians per second.
b2Vec2 localCenter
local center of mass position
Definition: b2Math.h:392
void SetLimits(float32 lower, float32 upper)
Set the joint limits in radians.
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
void EnableMotor(bool flag)
Enable/disable the joint motor.
A 2D column vector with 3 elements.
Definition: b2Math.h:143
void SetZero()
Set this vector to all zeros.
Definition: b2Math.h:152
A rigid body. These are created via b2World::CreateBody.
Definition: b2Body.h:126
b2Vec3 ey
Definition: b2Math.h:294
b2Vec2 v
Definition: b2TimeStep.h:58
float32 GetLowerLimit() const
Get the lower joint limit in radians.
float32 referenceAngle
The bodyB angle minus bodyA angle in the reference state (radians).
float32 x
Definition: b2Math.h:178
b2Vec2 localAnchorA
The local anchor point relative to bodyA&#39;s origin.
float32 m_invI
Definition: b2Body.h:458
GLint GLenum GLsizei GLint GLsizei const GLvoid * data
b2Body * m_bodyA
Definition: b2Joint.h:175
bool enableMotor
A flag to enable the joint motor.
b2Vec2 Solve(const b2Vec2 &b) const
Definition: b2Math.h:238
#define b2_angularSlop
Definition: b2Settings.h:72
float32 GetJointSpeed() const
Get the current joint angle speed in radians per second.
b2RevoluteJoint(const b2RevoluteJointDef *def)
float32 y
Definition: b2Math.h:139
b2Vec2 GetLocalPoint(const b2Vec2 &worldPoint) const
Definition: b2Body.h:566
b2Position * positions
Definition: b2TimeStep.h:66
b2Vec2 Solve22(const b2Vec2 &b) const
Definition: b2Math.cpp:41
#define b2Assert(A)
Definition: b2Settings.h:27
b2Vec3 Solve33(const b2Vec3 &b) const
Definition: b2Math.cpp:25
bool IsLimitEnabled() const
Is the joint limit enabled?
void Set(float32 angle)
Set using an angle in radians.
Definition: b2Math.h:311
T b2Clamp(T a, T low, T high)
Definition: b2Math.h:653
void SetMotorSpeed(float32 speed)
Set the motor speed in radians per second.
float32 lowerAngle
The lower angle for the joint limit (radians).
b2Vec2 ex
Definition: b2Math.h:252
T b2Abs(T a)
Definition: b2Math.h:615
A 2-by-2 matrix. Stored in column-major order.
Definition: b2Math.h:182
bool enableLimit
A flag to enable joint limits.
float32 m_maxMotorTorque
float32 m_angularVelocity
Definition: b2Body.h:440
void EnableLimit(bool flag)
Enable/disable the joint limit.
GLdouble angle
bool warmStarting
Definition: b2TimeStep.h:45
Rotation.
Definition: b2Math.h:298
float32 z
Definition: b2Math.h:178
float32 x
Definition: b2Math.h:139
b2Body * bodyA
The first attached body.
Definition: b2Joint.h:92
float32 a
world angles
Definition: b2Math.h:394
float32 dt
Definition: b2TimeStep.h:40
float32 Length() const
Get the length of this vector (the norm).
Definition: b2Math.h:100
float32 GetMotorTorque(float32 inv_dt) const
void SetAwake(bool flag)
Definition: b2Body.h:633
b2Body * bodyB
The second attached body.
Definition: b2Joint.h:95
b2Body * m_bodyB
Definition: b2Joint.h:176
b2Sweep m_sweep
Definition: b2Body.h:437
float float32
Definition: b2Settings.h:35
CArrayDouble< 6 > C
float32 GetReactionTorque(float32 inv_dt) const
GLdouble GLdouble GLdouble GLdouble GLdouble GLdouble f
float32 GetUpperLimit() const
Get the upper joint limit in radians.


mvsim
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autogenerated on Fri May 7 2021 03:05:51