2
* Copyright (c) 2006-2011 Erin Catto http://www.box2d.org
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.
19
#include <Box2D/Dynamics/Joints/b2RevoluteJoint.h>
20
#include <Box2D/Dynamics/b2Body.h>
21
#include <Box2D/Dynamics/b2TimeStep.h>
23
// Point-to-point constraint
26
// = v2 + cross(w2, r2) - v1 - cross(w1, r1)
27
// J = [-I -r1_skew I r2_skew ]
29
// w k % (rx i + ry j) = w * (-ry i + rx j)
36
void b2RevoluteJointDef::Initialize(b2Body* bA, b2Body* bB, const b2Vec2& anchor)
40
localAnchorA = bodyA->GetLocalPoint(anchor);
41
localAnchorB = bodyB->GetLocalPoint(anchor);
42
referenceAngle = bodyB->GetAngle() - bodyA->GetAngle();
45
b2RevoluteJoint::b2RevoluteJoint(const b2RevoluteJointDef* def)
48
m_localAnchorA = def->localAnchorA;
49
m_localAnchorB = def->localAnchorB;
50
m_referenceAngle = def->referenceAngle;
53
m_motorImpulse = 0.0f;
55
m_lowerAngle = def->lowerAngle;
56
m_upperAngle = def->upperAngle;
57
m_maxMotorTorque = def->maxMotorTorque;
58
m_motorSpeed = def->motorSpeed;
59
m_enableLimit = def->enableLimit;
60
m_enableMotor = def->enableMotor;
61
m_limitState = e_inactiveLimit;
64
void b2RevoluteJoint::InitVelocityConstraints(const b2SolverData& data)
66
m_indexA = m_bodyA->m_islandIndex;
67
m_indexB = m_bodyB->m_islandIndex;
68
m_localCenterA = m_bodyA->m_sweep.localCenter;
69
m_localCenterB = m_bodyB->m_sweep.localCenter;
70
m_invMassA = m_bodyA->m_invMass;
71
m_invMassB = m_bodyB->m_invMass;
72
m_invIA = m_bodyA->m_invI;
73
m_invIB = m_bodyB->m_invI;
75
b2Vec2 cA = data.positions[m_indexA].c;
76
float32 aA = data.positions[m_indexA].a;
77
b2Vec2 vA = data.velocities[m_indexA].v;
78
float32 wA = data.velocities[m_indexA].w;
80
b2Vec2 cB = data.positions[m_indexB].c;
81
float32 aB = data.positions[m_indexB].a;
82
b2Vec2 vB = data.velocities[m_indexB].v;
83
float32 wB = data.velocities[m_indexB].w;
87
m_rA = b2Mul(qA, m_localAnchorA - m_localCenterA);
88
m_rB = b2Mul(qB, m_localAnchorB - m_localCenterB);
90
// J = [-I -r1_skew I r2_skew]
95
// K = [ mA+r1y^2*iA+mB+r2y^2*iB, -r1y*iA*r1x-r2y*iB*r2x, -r1y*iA-r2y*iB]
96
// [ -r1y*iA*r1x-r2y*iB*r2x, mA+r1x^2*iA+mB+r2x^2*iB, r1x*iA+r2x*iB]
97
// [ -r1y*iA-r2y*iB, r1x*iA+r2x*iB, iA+iB]
99
float32 mA = m_invMassA, mB = m_invMassB;
100
float32 iA = m_invIA, iB = m_invIB;
102
bool fixedRotation = (iA + iB == 0.0f);
104
m_mass.ex.x = mA + mB + m_rA.y * m_rA.y * iA + m_rB.y * m_rB.y * iB;
105
m_mass.ey.x = -m_rA.y * m_rA.x * iA - m_rB.y * m_rB.x * iB;
106
m_mass.ez.x = -m_rA.y * iA - m_rB.y * iB;
107
m_mass.ex.y = m_mass.ey.x;
108
m_mass.ey.y = mA + mB + m_rA.x * m_rA.x * iA + m_rB.x * m_rB.x * iB;
109
m_mass.ez.y = m_rA.x * iA + m_rB.x * iB;
110
m_mass.ex.z = m_mass.ez.x;
111
m_mass.ey.z = m_mass.ez.y;
112
m_mass.ez.z = iA + iB;
114
m_motorMass = iA + iB;
115
if (m_motorMass > 0.0f)
117
m_motorMass = 1.0f / m_motorMass;
120
if (m_enableMotor == false || fixedRotation)
122
m_motorImpulse = 0.0f;
125
if (m_enableLimit && fixedRotation == false)
127
float32 jointAngle = aB - aA - m_referenceAngle;
128
if (b2Abs(m_upperAngle - m_lowerAngle) < 2.0f * b2_angularSlop)
130
m_limitState = e_equalLimits;
132
else if (jointAngle <= m_lowerAngle)
134
if (m_limitState != e_atLowerLimit)
138
m_limitState = e_atLowerLimit;
140
else if (jointAngle >= m_upperAngle)
142
if (m_limitState != e_atUpperLimit)
146
m_limitState = e_atUpperLimit;
150
m_limitState = e_inactiveLimit;
156
m_limitState = e_inactiveLimit;
159
if (data.step.warmStarting)
161
// Scale impulses to support a variable time step.
162
m_impulse *= data.step.dtRatio;
163
m_motorImpulse *= data.step.dtRatio;
165
b2Vec2 P(m_impulse.x, m_impulse.y);
168
wA -= iA * (b2Cross(m_rA, P) + m_motorImpulse + m_impulse.z);
171
wB += iB * (b2Cross(m_rB, P) + m_motorImpulse + m_impulse.z);
176
m_motorImpulse = 0.0f;
179
data.velocities[m_indexA].v = vA;
180
data.velocities[m_indexA].w = wA;
181
data.velocities[m_indexB].v = vB;
182
data.velocities[m_indexB].w = wB;
185
void b2RevoluteJoint::SolveVelocityConstraints(const b2SolverData& data)
187
b2Vec2 vA = data.velocities[m_indexA].v;
188
float32 wA = data.velocities[m_indexA].w;
189
b2Vec2 vB = data.velocities[m_indexB].v;
190
float32 wB = data.velocities[m_indexB].w;
192
float32 mA = m_invMassA, mB = m_invMassB;
193
float32 iA = m_invIA, iB = m_invIB;
195
bool fixedRotation = (iA + iB == 0.0f);
197
// Solve motor constraint.
198
if (m_enableMotor && m_limitState != e_equalLimits && fixedRotation == false)
200
float32 Cdot = wB - wA - m_motorSpeed;
201
float32 impulse = -m_motorMass * Cdot;
202
float32 oldImpulse = m_motorImpulse;
203
float32 maxImpulse = data.step.dt * m_maxMotorTorque;
204
m_motorImpulse = b2Clamp(m_motorImpulse + impulse, -maxImpulse, maxImpulse);
205
impulse = m_motorImpulse - oldImpulse;
211
// Solve limit constraint.
212
if (m_enableLimit && m_limitState != e_inactiveLimit && fixedRotation == false)
214
b2Vec2 Cdot1 = vB + b2Cross(wB, m_rB) - vA - b2Cross(wA, m_rA);
215
float32 Cdot2 = wB - wA;
216
b2Vec3 Cdot(Cdot1.x, Cdot1.y, Cdot2);
218
b2Vec3 impulse = -m_mass.Solve33(Cdot);
220
if (m_limitState == e_equalLimits)
222
m_impulse += impulse;
224
else if (m_limitState == e_atLowerLimit)
226
float32 newImpulse = m_impulse.z + impulse.z;
227
if (newImpulse < 0.0f)
229
b2Vec2 rhs = -Cdot1 + m_impulse.z * b2Vec2(m_mass.ez.x, m_mass.ez.y);
230
b2Vec2 reduced = m_mass.Solve22(rhs);
231
impulse.x = reduced.x;
232
impulse.y = reduced.y;
233
impulse.z = -m_impulse.z;
234
m_impulse.x += reduced.x;
235
m_impulse.y += reduced.y;
240
m_impulse += impulse;
243
else if (m_limitState == e_atUpperLimit)
245
float32 newImpulse = m_impulse.z + impulse.z;
246
if (newImpulse > 0.0f)
248
b2Vec2 rhs = -Cdot1 + m_impulse.z * b2Vec2(m_mass.ez.x, m_mass.ez.y);
249
b2Vec2 reduced = m_mass.Solve22(rhs);
250
impulse.x = reduced.x;
251
impulse.y = reduced.y;
252
impulse.z = -m_impulse.z;
253
m_impulse.x += reduced.x;
254
m_impulse.y += reduced.y;
259
m_impulse += impulse;
263
b2Vec2 P(impulse.x, impulse.y);
266
wA -= iA * (b2Cross(m_rA, P) + impulse.z);
269
wB += iB * (b2Cross(m_rB, P) + impulse.z);
273
// Solve point-to-point constraint
274
b2Vec2 Cdot = vB + b2Cross(wB, m_rB) - vA - b2Cross(wA, m_rA);
275
b2Vec2 impulse = m_mass.Solve22(-Cdot);
277
m_impulse.x += impulse.x;
278
m_impulse.y += impulse.y;
281
wA -= iA * b2Cross(m_rA, impulse);
284
wB += iB * b2Cross(m_rB, impulse);
287
data.velocities[m_indexA].v = vA;
288
data.velocities[m_indexA].w = wA;
289
data.velocities[m_indexB].v = vB;
290
data.velocities[m_indexB].w = wB;
293
bool b2RevoluteJoint::SolvePositionConstraints(const b2SolverData& data)
295
b2Vec2 cA = data.positions[m_indexA].c;
296
float32 aA = data.positions[m_indexA].a;
297
b2Vec2 cB = data.positions[m_indexB].c;
298
float32 aB = data.positions[m_indexB].a;
300
b2Rot qA(aA), qB(aB);
302
float32 angularError = 0.0f;
303
float32 positionError = 0.0f;
305
bool fixedRotation = (m_invIA + m_invIB == 0.0f);
307
// Solve angular limit constraint.
308
if (m_enableLimit && m_limitState != e_inactiveLimit && fixedRotation == false)
310
float32 angle = aB - aA - m_referenceAngle;
311
float32 limitImpulse = 0.0f;
313
if (m_limitState == e_equalLimits)
315
// Prevent large angular corrections
316
float32 C = b2Clamp(angle - m_lowerAngle, -b2_maxAngularCorrection, b2_maxAngularCorrection);
317
limitImpulse = -m_motorMass * C;
318
angularError = b2Abs(C);
320
else if (m_limitState == e_atLowerLimit)
322
float32 C = angle - m_lowerAngle;
325
// Prevent large angular corrections and allow some slop.
326
C = b2Clamp(C + b2_angularSlop, -b2_maxAngularCorrection, 0.0f);
327
limitImpulse = -m_motorMass * C;
329
else if (m_limitState == e_atUpperLimit)
331
float32 C = angle - m_upperAngle;
334
// Prevent large angular corrections and allow some slop.
335
C = b2Clamp(C - b2_angularSlop, 0.0f, b2_maxAngularCorrection);
336
limitImpulse = -m_motorMass * C;
339
aA -= m_invIA * limitImpulse;
340
aB += m_invIB * limitImpulse;
343
// Solve point-to-point constraint.
347
b2Vec2 rA = b2Mul(qA, m_localAnchorA - m_localCenterA);
348
b2Vec2 rB = b2Mul(qB, m_localAnchorB - m_localCenterB);
350
b2Vec2 C = cB + rB - cA - rA;
351
positionError = C.Length();
353
float32 mA = m_invMassA, mB = m_invMassB;
354
float32 iA = m_invIA, iB = m_invIB;
357
K.ex.x = mA + mB + iA * rA.y * rA.y + iB * rB.y * rB.y;
358
K.ex.y = -iA * rA.x * rA.y - iB * rB.x * rB.y;
360
K.ey.y = mA + mB + iA * rA.x * rA.x + iB * rB.x * rB.x;
362
b2Vec2 impulse = -K.Solve(C);
365
aA -= iA * b2Cross(rA, impulse);
368
aB += iB * b2Cross(rB, impulse);
371
data.positions[m_indexA].c = cA;
372
data.positions[m_indexA].a = aA;
373
data.positions[m_indexB].c = cB;
374
data.positions[m_indexB].a = aB;
376
return positionError <= b2_linearSlop && angularError <= b2_angularSlop;
379
b2Vec2 b2RevoluteJoint::GetAnchorA() const
381
return m_bodyA->GetWorldPoint(m_localAnchorA);
384
b2Vec2 b2RevoluteJoint::GetAnchorB() const
386
return m_bodyB->GetWorldPoint(m_localAnchorB);
389
b2Vec2 b2RevoluteJoint::GetReactionForce(float32 inv_dt) const
391
b2Vec2 P(m_impulse.x, m_impulse.y);
395
float32 b2RevoluteJoint::GetReactionTorque(float32 inv_dt) const
397
return inv_dt * m_impulse.z;
400
float32 b2RevoluteJoint::GetJointAngle() const
402
b2Body* bA = m_bodyA;
403
b2Body* bB = m_bodyB;
404
return bB->m_sweep.a - bA->m_sweep.a - m_referenceAngle;
407
float32 b2RevoluteJoint::GetJointSpeed() const
409
b2Body* bA = m_bodyA;
410
b2Body* bB = m_bodyB;
411
return bB->m_angularVelocity - bA->m_angularVelocity;
414
bool b2RevoluteJoint::IsMotorEnabled() const
416
return m_enableMotor;
419
void b2RevoluteJoint::EnableMotor(bool flag)
421
m_bodyA->SetAwake(true);
422
m_bodyB->SetAwake(true);
423
m_enableMotor = flag;
426
float32 b2RevoluteJoint::GetMotorTorque(float32 inv_dt) const
428
return inv_dt * m_motorImpulse;
431
void b2RevoluteJoint::SetMotorSpeed(float32 speed)
433
m_bodyA->SetAwake(true);
434
m_bodyB->SetAwake(true);
435
m_motorSpeed = speed;
438
void b2RevoluteJoint::SetMaxMotorTorque(float32 torque)
440
m_bodyA->SetAwake(true);
441
m_bodyB->SetAwake(true);
442
m_maxMotorTorque = torque;
445
bool b2RevoluteJoint::IsLimitEnabled() const
447
return m_enableLimit;
450
void b2RevoluteJoint::EnableLimit(bool flag)
452
if (flag != m_enableLimit)
454
m_bodyA->SetAwake(true);
455
m_bodyB->SetAwake(true);
456
m_enableLimit = flag;
461
float32 b2RevoluteJoint::GetLowerLimit() const
466
float32 b2RevoluteJoint::GetUpperLimit() const
471
void b2RevoluteJoint::SetLimits(float32 lower, float32 upper)
473
b2Assert(lower <= upper);
475
if (lower != m_lowerAngle || upper != m_upperAngle)
477
m_bodyA->SetAwake(true);
478
m_bodyB->SetAwake(true);
480
m_lowerAngle = lower;
481
m_upperAngle = upper;
485
void b2RevoluteJoint::Dump()
487
int32 indexA = m_bodyA->m_islandIndex;
488
int32 indexB = m_bodyB->m_islandIndex;
490
b2Log(" b2RevoluteJointDef jd;\n");
491
b2Log(" jd.bodyA = bodies[%d];\n", indexA);
492
b2Log(" jd.bodyB = bodies[%d];\n", indexB);
493
b2Log(" jd.collideConnected = bool(%d);\n", m_collideConnected);
494
b2Log(" jd.localAnchorA.Set(%.15lef, %.15lef);\n", m_localAnchorA.x, m_localAnchorA.y);
495
b2Log(" jd.localAnchorB.Set(%.15lef, %.15lef);\n", m_localAnchorB.x, m_localAnchorB.y);
496
b2Log(" jd.referenceAngle = %.15lef;\n", m_referenceAngle);
497
b2Log(" jd.enableLimit = bool(%d);\n", m_enableLimit);
498
b2Log(" jd.lowerAngle = %.15lef;\n", m_lowerAngle);
499
b2Log(" jd.upperAngle = %.15lef;\n", m_upperAngle);
500
b2Log(" jd.enableMotor = bool(%d);\n", m_enableMotor);
501
b2Log(" jd.motorSpeed = %.15lef;\n", m_motorSpeed);
502
b2Log(" jd.maxMotorTorque = %.15lef;\n", m_maxMotorTorque);
503
b2Log(" joints[%d] = m_world->CreateJoint(&jd);\n", m_index);