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 #include "b2RevoluteJoint.h"
20 #include "../b2Body.h"
21 #include "../b2World.h"
22
23 #include "../b2Island.h"
24
25 // Point-to-point constraint
26 // C = p2 - p1
27 // Cdot = v2 - v1
28 // = v2 + cross(w2, r2) - v1 - cross(w1, r1)
29 // J = [-I -r1_skew I r2_skew ]
30 // Identity used:
31 // w k % (rx i + ry j) = w * (-ry i + rx j)
32
33 // Motor constraint
34 // Cdot = w2 - w1
35 // J = [0 0 -1 0 0 1]
36 // K = invI1 + invI2
37
Initialize(b2Body * b1,b2Body * b2,const b2Vec2 & anchor)38 void b2RevoluteJointDef::Initialize(b2Body* b1, b2Body* b2, const b2Vec2& anchor)
39 {
40 body1 = b1;
41 body2 = b2;
42 localAnchor1 = body1->GetLocalPoint(anchor);
43 localAnchor2 = body2->GetLocalPoint(anchor);
44 referenceAngle = body2->GetAngle() - body1->GetAngle();
45 }
46
b2RevoluteJoint(const b2RevoluteJointDef * def)47 b2RevoluteJoint::b2RevoluteJoint(const b2RevoluteJointDef* def)
48 : b2Joint(def)
49 {
50 m_localAnchor1 = def->localAnchor1;
51 m_localAnchor2 = def->localAnchor2;
52 m_referenceAngle = def->referenceAngle;
53
54 m_pivotForce.Set(0.0f, 0.0f);
55 m_motorForce = 0.0f;
56 m_limitForce = 0.0f;
57 m_limitPositionImpulse = 0.0f;
58
59 m_lowerAngle = def->lowerAngle;
60 m_upperAngle = def->upperAngle;
61 m_maxMotorTorque = def->maxMotorTorque;
62 m_motorSpeed = def->motorSpeed;
63 m_enableLimit = def->enableLimit;
64 m_enableMotor = def->enableMotor;
65 }
66
InitVelocityConstraints(const b2TimeStep & step)67 void b2RevoluteJoint::InitVelocityConstraints(const b2TimeStep& step)
68 {
69 b2Body* b1 = m_body1;
70 b2Body* b2 = m_body2;
71
72 // Compute the effective mass matrix.
73 b2Vec2 r1 = b2Mul(b1->GetXForm().R, m_localAnchor1 - b1->GetLocalCenter());
74 b2Vec2 r2 = b2Mul(b2->GetXForm().R, m_localAnchor2 - b2->GetLocalCenter());
75
76 // K = [(1/m1 + 1/m2) * eye(2) - skew(r1) * invI1 * skew(r1) - skew(r2) * invI2 * skew(r2)]
77 // = [1/m1+1/m2 0 ] + invI1 * [r1.y*r1.y -r1.x*r1.y] + invI2 * [r1.y*r1.y -r1.x*r1.y]
78 // [ 0 1/m1+1/m2] [-r1.x*r1.y r1.x*r1.x] [-r1.x*r1.y r1.x*r1.x]
79 float32 invMass1 = b1->m_invMass, invMass2 = b2->m_invMass;
80 float32 invI1 = b1->m_invI, invI2 = b2->m_invI;
81
82 b2Mat22 K1;
83 K1.col1.x = invMass1 + invMass2; K1.col2.x = 0.0f;
84 K1.col1.y = 0.0f; K1.col2.y = invMass1 + invMass2;
85
86 b2Mat22 K2;
87 K2.col1.x = invI1 * r1.y * r1.y; K2.col2.x = -invI1 * r1.x * r1.y;
88 K2.col1.y = -invI1 * r1.x * r1.y; K2.col2.y = invI1 * r1.x * r1.x;
89
90 b2Mat22 K3;
91 K3.col1.x = invI2 * r2.y * r2.y; K3.col2.x = -invI2 * r2.x * r2.y;
92 K3.col1.y = -invI2 * r2.x * r2.y; K3.col2.y = invI2 * r2.x * r2.x;
93
94 b2Mat22 K = K1 + K2 + K3;
95 m_pivotMass = K.Invert();
96
97 m_motorMass = 1.0f / (invI1 + invI2);
98
99 if (m_enableMotor == false)
100 {
101 m_motorForce = 0.0f;
102 }
103
104 if (m_enableLimit)
105 {
106 float32 jointAngle = b2->m_sweep.a - b1->m_sweep.a - m_referenceAngle;
107 if (b2Abs(m_upperAngle - m_lowerAngle) < 2.0f * b2_angularSlop)
108 {
109 m_limitState = e_equalLimits;
110 }
111 else if (jointAngle <= m_lowerAngle)
112 {
113 if (m_limitState != e_atLowerLimit)
114 {
115 m_limitForce = 0.0f;
116 }
117 m_limitState = e_atLowerLimit;
118 }
119 else if (jointAngle >= m_upperAngle)
120 {
121 if (m_limitState != e_atUpperLimit)
122 {
123 m_limitForce = 0.0f;
124 }
125 m_limitState = e_atUpperLimit;
126 }
127 else
128 {
129 m_limitState = e_inactiveLimit;
130 m_limitForce = 0.0f;
131 }
132 }
133 else
134 {
135 m_limitForce = 0.0f;
136 }
137
138 if (step.warmStarting)
139 {
140 b1->m_linearVelocity -= B2FORCE_SCALE(step.dt) * invMass1 * m_pivotForce;
141 b1->m_angularVelocity -= B2FORCE_SCALE(step.dt) * invI1 * (b2Cross(r1, m_pivotForce) + B2FORCE_INV_SCALE(m_motorForce + m_limitForce));
142
143 b2->m_linearVelocity += B2FORCE_SCALE(step.dt) * invMass2 * m_pivotForce;
144 b2->m_angularVelocity += B2FORCE_SCALE(step.dt) * invI2 * (b2Cross(r2, m_pivotForce) + B2FORCE_INV_SCALE(m_motorForce + m_limitForce));
145 }
146 else
147 {
148 m_pivotForce.SetZero();
149 m_motorForce = 0.0f;
150 m_limitForce = 0.0f;
151 }
152
153 m_limitPositionImpulse = 0.0f;
154 }
155
SolveVelocityConstraints(const b2TimeStep & step)156 void b2RevoluteJoint::SolveVelocityConstraints(const b2TimeStep& step)
157 {
158 b2Body* b1 = m_body1;
159 b2Body* b2 = m_body2;
160
161 b2Vec2 r1 = b2Mul(b1->GetXForm().R, m_localAnchor1 - b1->GetLocalCenter());
162 b2Vec2 r2 = b2Mul(b2->GetXForm().R, m_localAnchor2 - b2->GetLocalCenter());
163
164 // Solve point-to-point constraint
165 b2Vec2 pivotCdot = b2->m_linearVelocity + b2Cross(b2->m_angularVelocity, r2) - b1->m_linearVelocity - b2Cross(b1->m_angularVelocity, r1);
166 b2Vec2 pivotForce = -B2FORCE_INV_SCALE(step.inv_dt) * b2Mul(m_pivotMass, pivotCdot);
167 m_pivotForce += pivotForce;
168
169 b2Vec2 P = B2FORCE_SCALE(step.dt) * pivotForce;
170 b1->m_linearVelocity -= b1->m_invMass * P;
171 b1->m_angularVelocity -= b1->m_invI * b2Cross(r1, P);
172
173 b2->m_linearVelocity += b2->m_invMass * P;
174 b2->m_angularVelocity += b2->m_invI * b2Cross(r2, P);
175
176 if (m_enableMotor && m_limitState != e_equalLimits)
177 {
178 float32 motorCdot = b2->m_angularVelocity - b1->m_angularVelocity - m_motorSpeed;
179 float32 motorForce = -step.inv_dt * m_motorMass * motorCdot;
180 float32 oldMotorForce = m_motorForce;
181 m_motorForce = b2Clamp(m_motorForce + motorForce, -m_maxMotorTorque, m_maxMotorTorque);
182 motorForce = m_motorForce - oldMotorForce;
183
184 float32 P = step.dt * motorForce;
185 b1->m_angularVelocity -= b1->m_invI * P;
186 b2->m_angularVelocity += b2->m_invI * P;
187 }
188
189 if (m_enableLimit && m_limitState != e_inactiveLimit)
190 {
191 float32 limitCdot = b2->m_angularVelocity - b1->m_angularVelocity;
192 float32 limitForce = -step.inv_dt * m_motorMass * limitCdot;
193
194 if (m_limitState == e_equalLimits)
195 {
196 m_limitForce += limitForce;
197 }
198 else if (m_limitState == e_atLowerLimit)
199 {
200 float32 oldLimitForce = m_limitForce;
201 m_limitForce = b2Max(m_limitForce + limitForce, 0.0f);
202 limitForce = m_limitForce - oldLimitForce;
203 }
204 else if (m_limitState == e_atUpperLimit)
205 {
206 float32 oldLimitForce = m_limitForce;
207 m_limitForce = b2Min(m_limitForce + limitForce, 0.0f);
208 limitForce = m_limitForce - oldLimitForce;
209 }
210
211 float32 P = step.dt * limitForce;
212 b1->m_angularVelocity -= b1->m_invI * P;
213 b2->m_angularVelocity += b2->m_invI * P;
214 }
215 }
216
SolvePositionConstraints()217 bool b2RevoluteJoint::SolvePositionConstraints()
218 {
219 b2Body* b1 = m_body1;
220 b2Body* b2 = m_body2;
221
222 float32 positionError = 0.0f;
223
224 // Solve point-to-point position error.
225 b2Vec2 r1 = b2Mul(b1->GetXForm().R, m_localAnchor1 - b1->GetLocalCenter());
226 b2Vec2 r2 = b2Mul(b2->GetXForm().R, m_localAnchor2 - b2->GetLocalCenter());
227
228 b2Vec2 p1 = b1->m_sweep.c + r1;
229 b2Vec2 p2 = b2->m_sweep.c + r2;
230 b2Vec2 ptpC = p2 - p1;
231
232 positionError = ptpC.Length();
233
234 // Prevent overly large corrections.
235 //b2Vec2 dpMax(b2_maxLinearCorrection, b2_maxLinearCorrection);
236 //ptpC = b2Clamp(ptpC, -dpMax, dpMax);
237
238 float32 invMass1 = b1->m_invMass, invMass2 = b2->m_invMass;
239 float32 invI1 = b1->m_invI, invI2 = b2->m_invI;
240
241 b2Mat22 K1;
242 K1.col1.x = invMass1 + invMass2; K1.col2.x = 0.0f;
243 K1.col1.y = 0.0f; K1.col2.y = invMass1 + invMass2;
244
245 b2Mat22 K2;
246 K2.col1.x = invI1 * r1.y * r1.y; K2.col2.x = -invI1 * r1.x * r1.y;
247 K2.col1.y = -invI1 * r1.x * r1.y; K2.col2.y = invI1 * r1.x * r1.x;
248
249 b2Mat22 K3;
250 K3.col1.x = invI2 * r2.y * r2.y; K3.col2.x = -invI2 * r2.x * r2.y;
251 K3.col1.y = -invI2 * r2.x * r2.y; K3.col2.y = invI2 * r2.x * r2.x;
252
253 b2Mat22 K = K1 + K2 + K3;
254 b2Vec2 impulse = K.Solve(-ptpC);
255
256 b1->m_sweep.c -= b1->m_invMass * impulse;
257 b1->m_sweep.a -= b1->m_invI * b2Cross(r1, impulse);
258
259 b2->m_sweep.c += b2->m_invMass * impulse;
260 b2->m_sweep.a += b2->m_invI * b2Cross(r2, impulse);
261
262 b1->SynchronizeTransform();
263 b2->SynchronizeTransform();
264
265 // Handle limits.
266 float32 angularError = 0.0f;
267
268 if (m_enableLimit && m_limitState != e_inactiveLimit)
269 {
270 float32 angle = b2->m_sweep.a - b1->m_sweep.a - m_referenceAngle;
271 float32 limitImpulse = 0.0f;
272
273 if (m_limitState == e_equalLimits)
274 {
275 // Prevent large angular corrections
276 float32 limitC = b2Clamp(angle, -b2_maxAngularCorrection, b2_maxAngularCorrection);
277 limitImpulse = -m_motorMass * limitC;
278 angularError = b2Abs(limitC);
279 }
280 else if (m_limitState == e_atLowerLimit)
281 {
282 float32 limitC = angle - m_lowerAngle;
283 angularError = b2Max(0.0f, -limitC);
284
285 // Prevent large angular corrections and allow some slop.
286 limitC = b2Clamp(limitC + b2_angularSlop, -b2_maxAngularCorrection, 0.0f);
287 limitImpulse = -m_motorMass * limitC;
288 float32 oldLimitImpulse = m_limitPositionImpulse;
289 m_limitPositionImpulse = b2Max(m_limitPositionImpulse + limitImpulse, 0.0f);
290 limitImpulse = m_limitPositionImpulse - oldLimitImpulse;
291 }
292 else if (m_limitState == e_atUpperLimit)
293 {
294 float32 limitC = angle - m_upperAngle;
295 angularError = b2Max(0.0f, limitC);
296
297 // Prevent large angular corrections and allow some slop.
298 limitC = b2Clamp(limitC - b2_angularSlop, 0.0f, b2_maxAngularCorrection);
299 limitImpulse = -m_motorMass * limitC;
300 float32 oldLimitImpulse = m_limitPositionImpulse;
301 m_limitPositionImpulse = b2Min(m_limitPositionImpulse + limitImpulse, 0.0f);
302 limitImpulse = m_limitPositionImpulse - oldLimitImpulse;
303 }
304
305 b1->m_sweep.a -= b1->m_invI * limitImpulse;
306 b2->m_sweep.a += b2->m_invI * limitImpulse;
307
308 b1->SynchronizeTransform();
309 b2->SynchronizeTransform();
310 }
311
312 return positionError <= b2_linearSlop && angularError <= b2_angularSlop;
313 }
314
GetAnchor1() const315 b2Vec2 b2RevoluteJoint::GetAnchor1() const
316 {
317 return m_body1->GetWorldPoint(m_localAnchor1);
318 }
319
GetAnchor2() const320 b2Vec2 b2RevoluteJoint::GetAnchor2() const
321 {
322 return m_body2->GetWorldPoint(m_localAnchor2);
323 }
324
GetReactionForce() const325 b2Vec2 b2RevoluteJoint::GetReactionForce() const
326 {
327 return B2FORCE_SCALE(float32(1.0))*m_pivotForce;
328 }
329
GetReactionTorque() const330 float32 b2RevoluteJoint::GetReactionTorque() const
331 {
332 return m_limitForce;
333 }
334
GetJointAngle() const335 float32 b2RevoluteJoint::GetJointAngle() const
336 {
337 b2Body* b1 = m_body1;
338 b2Body* b2 = m_body2;
339 return b2->m_sweep.a - b1->m_sweep.a - m_referenceAngle;
340 }
341
GetJointSpeed() const342 float32 b2RevoluteJoint::GetJointSpeed() const
343 {
344 b2Body* b1 = m_body1;
345 b2Body* b2 = m_body2;
346 return b2->m_angularVelocity - b1->m_angularVelocity;
347 }
348
IsMotorEnabled() const349 bool b2RevoluteJoint::IsMotorEnabled() const
350 {
351 return m_enableMotor;
352 }
353
EnableMotor(bool flag)354 void b2RevoluteJoint::EnableMotor(bool flag)
355 {
356 m_enableMotor = flag;
357 }
358
GetMotorTorque() const359 float32 b2RevoluteJoint::GetMotorTorque() const
360 {
361 return m_motorForce;
362 }
363
SetMotorSpeed(float32 speed)364 void b2RevoluteJoint::SetMotorSpeed(float32 speed)
365 {
366 m_motorSpeed = speed;
367 }
368
SetMaxMotorTorque(float32 torque)369 void b2RevoluteJoint::SetMaxMotorTorque(float32 torque)
370 {
371 m_maxMotorTorque = torque;
372 }
373
IsLimitEnabled() const374 bool b2RevoluteJoint::IsLimitEnabled() const
375 {
376 return m_enableLimit;
377 }
378
EnableLimit(bool flag)379 void b2RevoluteJoint::EnableLimit(bool flag)
380 {
381 m_enableLimit = flag;
382 }
383
GetLowerLimit() const384 float32 b2RevoluteJoint::GetLowerLimit() const
385 {
386 return m_lowerAngle;
387 }
388
GetUpperLimit() const389 float32 b2RevoluteJoint::GetUpperLimit() const
390 {
391 return m_upperAngle;
392 }
393
SetLimits(float32 lower,float32 upper)394 void b2RevoluteJoint::SetLimits(float32 lower, float32 upper)
395 {
396 b2Assert(lower <= upper);
397 m_lowerAngle = lower;
398 m_upperAngle = upper;
399 }
400