selove / src / libraries / Box2D / Dynamics / Contacts / b2ContactSolver.cpp

The default branch has multiple heads

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
/*
* Copyright (c) 2006-2011 Erin Catto http://www.box2d.org
*
* This software is provided 'as-is', without any express or implied
* warranty.  In no event will the authors be held liable for any damages
* arising from the use of this software.
* Permission is granted to anyone to use this software for any purpose,
* including commercial applications, and to alter it and redistribute it
* freely, subject to the following restrictions:
* 1. The origin of this software must not be misrepresented; you must not
* claim that you wrote the original software. If you use this software
* in a product, an acknowledgment in the product documentation would be
* appreciated but is not required.
* 2. Altered source versions must be plainly marked as such, and must not be
* misrepresented as being the original software.
* 3. This notice may not be removed or altered from any source distribution.
*/

#include <Box2D/Dynamics/Contacts/b2ContactSolver.h>

#include <Box2D/Dynamics/Contacts/b2Contact.h>
#include <Box2D/Dynamics/b2Body.h>
#include <Box2D/Dynamics/b2Fixture.h>
#include <Box2D/Dynamics/b2World.h>
#include <Box2D/Common/b2StackAllocator.h>

#define B2_DEBUG_SOLVER 0

struct b2ContactPositionConstraint
{
	b2Vec2 localPoints[b2_maxManifoldPoints];
	b2Vec2 localNormal;
	b2Vec2 localPoint;
	int32 indexA;
	int32 indexB;
	float32 invMassA, invMassB;
	b2Vec2 localCenterA, localCenterB;
	float32 invIA, invIB;
	b2Manifold::Type type;
	float32 radiusA, radiusB;
	int32 pointCount;
};

b2ContactSolver::b2ContactSolver(b2ContactSolverDef* def)
{
	m_step = def->step;
	m_allocator = def->allocator;
	m_count = def->count;
	m_positionConstraints = (b2ContactPositionConstraint*)m_allocator->Allocate(m_count * sizeof(b2ContactPositionConstraint));
	m_velocityConstraints = (b2ContactVelocityConstraint*)m_allocator->Allocate(m_count * sizeof(b2ContactVelocityConstraint));
	m_positions = def->positions;
	m_velocities = def->velocities;
	m_contacts = def->contacts;

	// Initialize position independent portions of the constraints.
	for (int32 i = 0; i < m_count; ++i)
	{
		b2Contact* contact = m_contacts[i];

		b2Fixture* fixtureA = contact->m_fixtureA;
		b2Fixture* fixtureB = contact->m_fixtureB;
		b2Shape* shapeA = fixtureA->GetShape();
		b2Shape* shapeB = fixtureB->GetShape();
		float32 radiusA = shapeA->m_radius;
		float32 radiusB = shapeB->m_radius;
		b2Body* bodyA = fixtureA->GetBody();
		b2Body* bodyB = fixtureB->GetBody();
		b2Manifold* manifold = contact->GetManifold();

		int32 pointCount = manifold->pointCount;
		b2Assert(pointCount > 0);

		b2ContactVelocityConstraint* vc = m_velocityConstraints + i;
		vc->friction = contact->m_friction;
		vc->restitution = contact->m_restitution;
		vc->indexA = bodyA->m_islandIndex;
		vc->indexB = bodyB->m_islandIndex;
		vc->invMassA = bodyA->m_invMass;
		vc->invMassB = bodyB->m_invMass;
		vc->invIA = bodyA->m_invI;
		vc->invIB = bodyB->m_invI;
		vc->contactIndex = i;
		vc->pointCount = pointCount;
		vc->K.SetZero();
		vc->normalMass.SetZero();

		b2ContactPositionConstraint* pc = m_positionConstraints + i;
		pc->indexA = bodyA->m_islandIndex;
		pc->indexB = bodyB->m_islandIndex;
		pc->invMassA = bodyA->m_invMass;
		pc->invMassB = bodyB->m_invMass;
		pc->localCenterA = bodyA->m_sweep.localCenter;
		pc->localCenterB = bodyB->m_sweep.localCenter;
		pc->invIA = bodyA->m_invI;
		pc->invIB = bodyB->m_invI;
		pc->localNormal = manifold->localNormal;
		pc->localPoint = manifold->localPoint;
		pc->pointCount = pointCount;
		pc->radiusA = radiusA;
		pc->radiusB = radiusB;
		pc->type = manifold->type;

		for (int32 j = 0; j < pointCount; ++j)
		{
			b2ManifoldPoint* cp = manifold->points + j;
			b2VelocityConstraintPoint* vcp = vc->points + j;
	
			if (m_step.warmStarting)
			{
				vcp->normalImpulse = m_step.dtRatio * cp->normalImpulse;
				vcp->tangentImpulse = m_step.dtRatio * cp->tangentImpulse;
			}
			else
			{
				vcp->normalImpulse = 0.0f;
				vcp->tangentImpulse = 0.0f;
			}

			vcp->rA.SetZero();
			vcp->rB.SetZero();
			vcp->normalMass = 0.0f;
			vcp->tangentMass = 0.0f;
			vcp->velocityBias = 0.0f;

			pc->localPoints[j] = cp->localPoint;
		}
	}
}

b2ContactSolver::~b2ContactSolver()
{
	m_allocator->Free(m_velocityConstraints);
	m_allocator->Free(m_positionConstraints);
}

// Initialize position dependent portions of the velocity constraints.
void b2ContactSolver::InitializeVelocityConstraints()
{
	for (int32 i = 0; i < m_count; ++i)
	{
		b2ContactVelocityConstraint* vc = m_velocityConstraints + i;
		b2ContactPositionConstraint* pc = m_positionConstraints + i;

		float32 radiusA = pc->radiusA;
		float32 radiusB = pc->radiusB;
		b2Manifold* manifold = m_contacts[vc->contactIndex]->GetManifold();

		int32 indexA = vc->indexA;
		int32 indexB = vc->indexB;

		float32 mA = vc->invMassA;
		float32 mB = vc->invMassB;
		float32 iA = vc->invIA;
		float32 iB = vc->invIB;
		b2Vec2 localCenterA = pc->localCenterA;
		b2Vec2 localCenterB = pc->localCenterB;

		b2Vec2 cA = m_positions[indexA].c;
		float32 aA = m_positions[indexA].a;
		b2Vec2 vA = m_velocities[indexA].v;
		float32 wA = m_velocities[indexA].w;

		b2Vec2 cB = m_positions[indexB].c;
		float32 aB = m_positions[indexB].a;
		b2Vec2 vB = m_velocities[indexB].v;
		float32 wB = m_velocities[indexB].w;

		b2Assert(manifold->pointCount > 0);

		b2Transform xfA, xfB;
		xfA.q.Set(aA);
		xfB.q.Set(aB);
		xfA.p = cA - b2Mul(xfA.q, localCenterA);
		xfB.p = cB - b2Mul(xfB.q, localCenterB);

		b2WorldManifold worldManifold;
		worldManifold.Initialize(manifold, xfA, radiusA, xfB, radiusB);

		vc->normal = worldManifold.normal;

		int32 pointCount = vc->pointCount;
		for (int32 j = 0; j < pointCount; ++j)
		{
			b2VelocityConstraintPoint* vcp = vc->points + j;

			vcp->rA = worldManifold.points[j] - cA;
			vcp->rB = worldManifold.points[j] - cB;

			float32 rnA = b2Cross(vcp->rA, vc->normal);
			float32 rnB = b2Cross(vcp->rB, vc->normal);

			float32 kNormal = mA + mB + iA * rnA * rnA + iB * rnB * rnB;

			vcp->normalMass = kNormal > 0.0f ? 1.0f / kNormal : 0.0f;

			b2Vec2 tangent = b2Cross(vc->normal, 1.0f);

			float32 rtA = b2Cross(vcp->rA, tangent);
			float32 rtB = b2Cross(vcp->rB, tangent);

			float32 kTangent = mA + mB + iA * rtA * rtA + iB * rtB * rtB;

			vcp->tangentMass = kTangent > 0.0f ? 1.0f /  kTangent : 0.0f;

			// Setup a velocity bias for restitution.
			vcp->velocityBias = 0.0f;
			float32 vRel = b2Dot(vc->normal, vB + b2Cross(wB, vcp->rB) - vA - b2Cross(wA, vcp->rA));
			if (vRel < -b2_velocityThreshold)
			{
				vcp->velocityBias = -vc->restitution * vRel;
			}
		}

		// If we have two points, then prepare the block solver.
		if (vc->pointCount == 2)
		{
			b2VelocityConstraintPoint* vcp1 = vc->points + 0;
			b2VelocityConstraintPoint* vcp2 = vc->points + 1;

			float32 rn1A = b2Cross(vcp1->rA, vc->normal);
			float32 rn1B = b2Cross(vcp1->rB, vc->normal);
			float32 rn2A = b2Cross(vcp2->rA, vc->normal);
			float32 rn2B = b2Cross(vcp2->rB, vc->normal);

			float32 k11 = mA + mB + iA * rn1A * rn1A + iB * rn1B * rn1B;
			float32 k22 = mA + mB + iA * rn2A * rn2A + iB * rn2B * rn2B;
			float32 k12 = mA + mB + iA * rn1A * rn2A + iB * rn1B * rn2B;

			// Ensure a reasonable condition number.
			const float32 k_maxConditionNumber = 1000.0f;
			if (k11 * k11 < k_maxConditionNumber * (k11 * k22 - k12 * k12))
			{
				// K is safe to invert.
				vc->K.ex.Set(k11, k12);
				vc->K.ey.Set(k12, k22);
				vc->normalMass = vc->K.GetInverse();
			}
			else
			{
				// The constraints are redundant, just use one.
				// TODO_ERIN use deepest?
				vc->pointCount = 1;
			}
		}
	}
}

void b2ContactSolver::WarmStart()
{
	// Warm start.
	for (int32 i = 0; i < m_count; ++i)
	{
		b2ContactVelocityConstraint* vc = m_velocityConstraints + i;

		int32 indexA = vc->indexA;
		int32 indexB = vc->indexB;
		float32 mA = vc->invMassA;
		float32 iA = vc->invIA;
		float32 mB = vc->invMassB;
		float32 iB = vc->invIB;
		int32 pointCount = vc->pointCount;

		b2Vec2 vA = m_velocities[indexA].v;
		float32 wA = m_velocities[indexA].w;
		b2Vec2 vB = m_velocities[indexB].v;
		float32 wB = m_velocities[indexB].w;

		b2Vec2 normal = vc->normal;
		b2Vec2 tangent = b2Cross(normal, 1.0f);

		for (int32 j = 0; j < pointCount; ++j)
		{
			b2VelocityConstraintPoint* vcp = vc->points + j;
			b2Vec2 P = vcp->normalImpulse * normal + vcp->tangentImpulse * tangent;
			wA -= iA * b2Cross(vcp->rA, P);
			vA -= mA * P;
			wB += iB * b2Cross(vcp->rB, P);
			vB += mB * P;
		}

		m_velocities[indexA].v = vA;
		m_velocities[indexA].w = wA;
		m_velocities[indexB].v = vB;
		m_velocities[indexB].w = wB;
	}
}

void b2ContactSolver::SolveVelocityConstraints()
{
	for (int32 i = 0; i < m_count; ++i)
	{
		b2ContactVelocityConstraint* vc = m_velocityConstraints + i;

		int32 indexA = vc->indexA;
		int32 indexB = vc->indexB;
		float32 mA = vc->invMassA;
		float32 iA = vc->invIA;
		float32 mB = vc->invMassB;
		float32 iB = vc->invIB;
		int32 pointCount = vc->pointCount;

		b2Vec2 vA = m_velocities[indexA].v;
		float32 wA = m_velocities[indexA].w;
		b2Vec2 vB = m_velocities[indexB].v;
		float32 wB = m_velocities[indexB].w;

		b2Vec2 normal = vc->normal;
		b2Vec2 tangent = b2Cross(normal, 1.0f);
		float32 friction = vc->friction;

		b2Assert(pointCount == 1 || pointCount == 2);

		// Solve tangent constraints first because non-penetration is more important
		// than friction.
		for (int32 j = 0; j < pointCount; ++j)
		{
			b2VelocityConstraintPoint* vcp = vc->points + j;

			// Relative velocity at contact
			b2Vec2 dv = vB + b2Cross(wB, vcp->rB) - vA - b2Cross(wA, vcp->rA);

			// Compute tangent force
			float32 vt = b2Dot(dv, tangent);
			float32 lambda = vcp->tangentMass * (-vt);

			// b2Clamp the accumulated force
			float32 maxFriction = friction * vcp->normalImpulse;
			float32 newImpulse = b2Clamp(vcp->tangentImpulse + lambda, -maxFriction, maxFriction);
			lambda = newImpulse - vcp->tangentImpulse;
			vcp->tangentImpulse = newImpulse;

			// Apply contact impulse
			b2Vec2 P = lambda * tangent;

			vA -= mA * P;
			wA -= iA * b2Cross(vcp->rA, P);

			vB += mB * P;
			wB += iB * b2Cross(vcp->rB, P);
		}

		// Solve normal constraints
		if (vc->pointCount == 1)
		{
			b2VelocityConstraintPoint* vcp = vc->points + 0;

			// Relative velocity at contact
			b2Vec2 dv = vB + b2Cross(wB, vcp->rB) - vA - b2Cross(wA, vcp->rA);

			// Compute normal impulse
			float32 vn = b2Dot(dv, normal);
			float32 lambda = -vcp->normalMass * (vn - vcp->velocityBias);

			// b2Clamp the accumulated impulse
			float32 newImpulse = b2Max(vcp->normalImpulse + lambda, 0.0f);
			lambda = newImpulse - vcp->normalImpulse;
			vcp->normalImpulse = newImpulse;

			// Apply contact impulse
			b2Vec2 P = lambda * normal;
			vA -= mA * P;
			wA -= iA * b2Cross(vcp->rA, P);

			vB += mB * P;
			wB += iB * b2Cross(vcp->rB, P);
		}
		else
		{
			// Block solver developed in collaboration with Dirk Gregorius (back in 01/07 on Box2D_Lite).
			// Build the mini LCP for this contact patch
			//
			// vn = A * x + b, vn >= 0, , vn >= 0, x >= 0 and vn_i * x_i = 0 with i = 1..2
			//
			// A = J * W * JT and J = ( -n, -r1 x n, n, r2 x n )
			// b = vn0 - velocityBias
			//
			// The system is solved using the "Total enumeration method" (s. Murty). The complementary constraint vn_i * x_i
			// implies that we must have in any solution either vn_i = 0 or x_i = 0. So for the 2D contact problem the cases
			// vn1 = 0 and vn2 = 0, x1 = 0 and x2 = 0, x1 = 0 and vn2 = 0, x2 = 0 and vn1 = 0 need to be tested. The first valid
			// solution that satisfies the problem is chosen.
			// 
			// In order to account of the accumulated impulse 'a' (because of the iterative nature of the solver which only requires
			// that the accumulated impulse is clamped and not the incremental impulse) we change the impulse variable (x_i).
			//
			// Substitute:
			// 
			// x = a + d
			// 
			// a := old total impulse
			// x := new total impulse
			// d := incremental impulse 
			//
			// For the current iteration we extend the formula for the incremental impulse
			// to compute the new total impulse:
			//
			// vn = A * d + b
			//    = A * (x - a) + b
			//    = A * x + b - A * a
			//    = A * x + b'
			// b' = b - A * a;

			b2VelocityConstraintPoint* cp1 = vc->points + 0;
			b2VelocityConstraintPoint* cp2 = vc->points + 1;

			b2Vec2 a(cp1->normalImpulse, cp2->normalImpulse);
			b2Assert(a.x >= 0.0f && a.y >= 0.0f);

			// Relative velocity at contact
			b2Vec2 dv1 = vB + b2Cross(wB, cp1->rB) - vA - b2Cross(wA, cp1->rA);
			b2Vec2 dv2 = vB + b2Cross(wB, cp2->rB) - vA - b2Cross(wA, cp2->rA);

			// Compute normal velocity
			float32 vn1 = b2Dot(dv1, normal);
			float32 vn2 = b2Dot(dv2, normal);

			b2Vec2 b;
			b.x = vn1 - cp1->velocityBias;
			b.y = vn2 - cp2->velocityBias;

			// Compute b'
			b -= b2Mul(vc->K, a);

			const float32 k_errorTol = 1e-3f;
			B2_NOT_USED(k_errorTol);

			for (;;)
			{
				//
				// Case 1: vn = 0
				//
				// 0 = A * x + b'
				//
				// Solve for x:
				//
				// x = - inv(A) * b'
				//
				b2Vec2 x = - b2Mul(vc->normalMass, b);

				if (x.x >= 0.0f && x.y >= 0.0f)
				{
					// Get the incremental impulse
					b2Vec2 d = x - a;

					// Apply incremental impulse
					b2Vec2 P1 = d.x * normal;
					b2Vec2 P2 = d.y * normal;
					vA -= mA * (P1 + P2);
					wA -= iA * (b2Cross(cp1->rA, P1) + b2Cross(cp2->rA, P2));

					vB += mB * (P1 + P2);
					wB += iB * (b2Cross(cp1->rB, P1) + b2Cross(cp2->rB, P2));

					// Accumulate
					cp1->normalImpulse = x.x;
					cp2->normalImpulse = x.y;

#if B2_DEBUG_SOLVER == 1
					// Postconditions
					dv1 = vB + b2Cross(wB, cp1->rB) - vA - b2Cross(wA, cp1->rA);
					dv2 = vB + b2Cross(wB, cp2->rB) - vA - b2Cross(wA, cp2->rA);

					// Compute normal velocity
					vn1 = b2Dot(dv1, normal);
					vn2 = b2Dot(dv2, normal);

					b2Assert(b2Abs(vn1 - cp1->velocityBias) < k_errorTol);
					b2Assert(b2Abs(vn2 - cp2->velocityBias) < k_errorTol);
#endif
					break;
				}

				//
				// Case 2: vn1 = 0 and x2 = 0
				//
				//   0 = a11 * x1 + a12 * 0 + b1' 
				// vn2 = a21 * x1 + a22 * 0 + b2'
				//
				x.x = - cp1->normalMass * b.x;
				x.y = 0.0f;
				vn1 = 0.0f;
				vn2 = vc->K.ex.y * x.x + b.y;

				if (x.x >= 0.0f && vn2 >= 0.0f)
				{
					// Get the incremental impulse
					b2Vec2 d = x - a;

					// Apply incremental impulse
					b2Vec2 P1 = d.x * normal;
					b2Vec2 P2 = d.y * normal;
					vA -= mA * (P1 + P2);
					wA -= iA * (b2Cross(cp1->rA, P1) + b2Cross(cp2->rA, P2));

					vB += mB * (P1 + P2);
					wB += iB * (b2Cross(cp1->rB, P1) + b2Cross(cp2->rB, P2));

					// Accumulate
					cp1->normalImpulse = x.x;
					cp2->normalImpulse = x.y;

#if B2_DEBUG_SOLVER == 1
					// Postconditions
					dv1 = vB + b2Cross(wB, cp1->rB) - vA - b2Cross(wA, cp1->rA);

					// Compute normal velocity
					vn1 = b2Dot(dv1, normal);

					b2Assert(b2Abs(vn1 - cp1->velocityBias) < k_errorTol);
#endif
					break;
				}


				//
				// Case 3: vn2 = 0 and x1 = 0
				//
				// vn1 = a11 * 0 + a12 * x2 + b1' 
				//   0 = a21 * 0 + a22 * x2 + b2'
				//
				x.x = 0.0f;
				x.y = - cp2->normalMass * b.y;
				vn1 = vc->K.ey.x * x.y + b.x;
				vn2 = 0.0f;

				if (x.y >= 0.0f && vn1 >= 0.0f)
				{
					// Resubstitute for the incremental impulse
					b2Vec2 d = x - a;

					// Apply incremental impulse
					b2Vec2 P1 = d.x * normal;
					b2Vec2 P2 = d.y * normal;
					vA -= mA * (P1 + P2);
					wA -= iA * (b2Cross(cp1->rA, P1) + b2Cross(cp2->rA, P2));

					vB += mB * (P1 + P2);
					wB += iB * (b2Cross(cp1->rB, P1) + b2Cross(cp2->rB, P2));

					// Accumulate
					cp1->normalImpulse = x.x;
					cp2->normalImpulse = x.y;

#if B2_DEBUG_SOLVER == 1
					// Postconditions
					dv2 = vB + b2Cross(wB, cp2->rB) - vA - b2Cross(wA, cp2->rA);

					// Compute normal velocity
					vn2 = b2Dot(dv2, normal);

					b2Assert(b2Abs(vn2 - cp2->velocityBias) < k_errorTol);
#endif
					break;
				}

				//
				// Case 4: x1 = 0 and x2 = 0
				// 
				// vn1 = b1
				// vn2 = b2;
				x.x = 0.0f;
				x.y = 0.0f;
				vn1 = b.x;
				vn2 = b.y;

				if (vn1 >= 0.0f && vn2 >= 0.0f )
				{
					// Resubstitute for the incremental impulse
					b2Vec2 d = x - a;

					// Apply incremental impulse
					b2Vec2 P1 = d.x * normal;
					b2Vec2 P2 = d.y * normal;
					vA -= mA * (P1 + P2);
					wA -= iA * (b2Cross(cp1->rA, P1) + b2Cross(cp2->rA, P2));

					vB += mB * (P1 + P2);
					wB += iB * (b2Cross(cp1->rB, P1) + b2Cross(cp2->rB, P2));

					// Accumulate
					cp1->normalImpulse = x.x;
					cp2->normalImpulse = x.y;

					break;
				}

				// No solution, give up. This is hit sometimes, but it doesn't seem to matter.
				break;
			}
		}

		m_velocities[indexA].v = vA;
		m_velocities[indexA].w = wA;
		m_velocities[indexB].v = vB;
		m_velocities[indexB].w = wB;
	}
}

void b2ContactSolver::StoreImpulses()
{
	for (int32 i = 0; i < m_count; ++i)
	{
		b2ContactVelocityConstraint* vc = m_velocityConstraints + i;
		b2Manifold* manifold = m_contacts[vc->contactIndex]->GetManifold();

		for (int32 j = 0; j < vc->pointCount; ++j)
		{
			manifold->points[j].normalImpulse = vc->points[j].normalImpulse;
			manifold->points[j].tangentImpulse = vc->points[j].tangentImpulse;
		}
	}
}

struct b2PositionSolverManifold
{
	void Initialize(b2ContactPositionConstraint* pc, const b2Transform& xfA, const b2Transform& xfB, int32 index)
	{
		b2Assert(pc->pointCount > 0);

		switch (pc->type)
		{
		case b2Manifold::e_circles:
			{
				b2Vec2 pointA = b2Mul(xfA, pc->localPoint);
				b2Vec2 pointB = b2Mul(xfB, pc->localPoints[0]);
				normal = pointB - pointA;
				normal.Normalize();
				point = 0.5f * (pointA + pointB);
				separation = b2Dot(pointB - pointA, normal) - pc->radiusA - pc->radiusB;
			}
			break;

		case b2Manifold::e_faceA:
			{
				normal = b2Mul(xfA.q, pc->localNormal);
				b2Vec2 planePoint = b2Mul(xfA, pc->localPoint);

				b2Vec2 clipPoint = b2Mul(xfB, pc->localPoints[index]);
				separation = b2Dot(clipPoint - planePoint, normal) - pc->radiusA - pc->radiusB;
				point = clipPoint;
			}
			break;

		case b2Manifold::e_faceB:
			{
				normal = b2Mul(xfB.q, pc->localNormal);
				b2Vec2 planePoint = b2Mul(xfB, pc->localPoint);

				b2Vec2 clipPoint = b2Mul(xfA, pc->localPoints[index]);
				separation = b2Dot(clipPoint - planePoint, normal) - pc->radiusA - pc->radiusB;
				point = clipPoint;

				// Ensure normal points from A to B
				normal = -normal;
			}
			break;
		}
	}

	b2Vec2 normal;
	b2Vec2 point;
	float32 separation;
};

// Sequential solver.
bool b2ContactSolver::SolvePositionConstraints()
{
	float32 minSeparation = 0.0f;

	for (int32 i = 0; i < m_count; ++i)
	{
		b2ContactPositionConstraint* pc = m_positionConstraints + i;

		int32 indexA = pc->indexA;
		int32 indexB = pc->indexB;
		b2Vec2 localCenterA = pc->localCenterA;
		float32 mA = pc->invMassA;
		float32 iA = pc->invIA;
		b2Vec2 localCenterB = pc->localCenterB;
		float32 mB = pc->invMassB;
		float32 iB = pc->invIB;
		int32 pointCount = pc->pointCount;

		b2Vec2 cA = m_positions[indexA].c;
		float32 aA = m_positions[indexA].a;

		b2Vec2 cB = m_positions[indexB].c;
		float32 aB = m_positions[indexB].a;

		// Solve normal constraints
		for (int32 j = 0; j < pointCount; ++j)
		{
			b2Transform xfA, xfB;
			xfA.q.Set(aA);
			xfB.q.Set(aB);
			xfA.p = cA - b2Mul(xfA.q, localCenterA);
			xfB.p = cB - b2Mul(xfB.q, localCenterB);

			b2PositionSolverManifold psm;
			psm.Initialize(pc, xfA, xfB, j);
			b2Vec2 normal = psm.normal;

			b2Vec2 point = psm.point;
			float32 separation = psm.separation;

			b2Vec2 rA = point - cA;
			b2Vec2 rB = point - cB;

			// Track max constraint error.
			minSeparation = b2Min(minSeparation, separation);

			// Prevent large corrections and allow slop.
			float32 C = b2Clamp(b2_baumgarte * (separation + b2_linearSlop), -b2_maxLinearCorrection, 0.0f);

			// Compute the effective mass.
			float32 rnA = b2Cross(rA, normal);
			float32 rnB = b2Cross(rB, normal);
			float32 K = mA + mB + iA * rnA * rnA + iB * rnB * rnB;

			// Compute normal impulse
			float32 impulse = K > 0.0f ? - C / K : 0.0f;

			b2Vec2 P = impulse * normal;

			cA -= mA * P;
			aA -= iA * b2Cross(rA, P);

			cB += mB * P;
			aB += iB * b2Cross(rB, P);
		}

		m_positions[indexA].c = cA;
		m_positions[indexA].a = aA;

		m_positions[indexB].c = cB;
		m_positions[indexB].a = aB;
	}

	// We can't expect minSpeparation >= -b2_linearSlop because we don't
	// push the separation above -b2_linearSlop.
	return minSeparation >= -3.0f * b2_linearSlop;
}

// Sequential position solver for position constraints.
bool b2ContactSolver::SolveTOIPositionConstraints(int32 toiIndexA, int32 toiIndexB)
{
	float32 minSeparation = 0.0f;

	for (int32 i = 0; i < m_count; ++i)
	{
		b2ContactPositionConstraint* pc = m_positionConstraints + i;

		int32 indexA = pc->indexA;
		int32 indexB = pc->indexB;
		b2Vec2 localCenterA = pc->localCenterA;
		b2Vec2 localCenterB = pc->localCenterB;
		int32 pointCount = pc->pointCount;

		float32 mA = 0.0f;
		float32 iA = 0.0f;
		if (indexA == toiIndexA || indexA == toiIndexB)
		{
			mA = pc->invMassA;
			iA = pc->invIA;
		}

		float32 mB = pc->invMassB;
		float32 iB = pc->invIB;
		if (indexB == toiIndexA || indexB == toiIndexB)
		{
			mB = pc->invMassB;
			iB = pc->invIB;
		}

		b2Vec2 cA = m_positions[indexA].c;
		float32 aA = m_positions[indexA].a;

		b2Vec2 cB = m_positions[indexB].c;
		float32 aB = m_positions[indexB].a;

		// Solve normal constraints
		for (int32 j = 0; j < pointCount; ++j)
		{
			b2Transform xfA, xfB;
			xfA.q.Set(aA);
			xfB.q.Set(aB);
			xfA.p = cA - b2Mul(xfA.q, localCenterA);
			xfB.p = cB - b2Mul(xfB.q, localCenterB);

			b2PositionSolverManifold psm;
			psm.Initialize(pc, xfA, xfB, j);
			b2Vec2 normal = psm.normal;

			b2Vec2 point = psm.point;
			float32 separation = psm.separation;

			b2Vec2 rA = point - cA;
			b2Vec2 rB = point - cB;

			// Track max constraint error.
			minSeparation = b2Min(minSeparation, separation);

			// Prevent large corrections and allow slop.
			float32 C = b2Clamp(b2_toiBaugarte * (separation + b2_linearSlop), -b2_maxLinearCorrection, 0.0f);

			// Compute the effective mass.
			float32 rnA = b2Cross(rA, normal);
			float32 rnB = b2Cross(rB, normal);
			float32 K = mA + mB + iA * rnA * rnA + iB * rnB * rnB;

			// Compute normal impulse
			float32 impulse = K > 0.0f ? - C / K : 0.0f;

			b2Vec2 P = impulse * normal;

			cA -= mA * P;
			aA -= iA * b2Cross(rA, P);

			cB += mB * P;
			aB += iB * b2Cross(rB, P);
		}

		m_positions[indexA].c = cA;
		m_positions[indexA].a = aA;

		m_positions[indexB].c = cB;
		m_positions[indexB].a = aB;
	}

	// We can't expect minSpeparation >= -b2_linearSlop because we don't
	// push the separation above -b2_linearSlop.
	return minSeparation >= -1.5f * b2_linearSlop;
}
Tip: Filter by directory path e.g. /media app.js to search for public/media/app.js.
Tip: Use camelCasing e.g. ProjME to search for ProjectModifiedEvent.java.
Tip: Filter by extension type e.g. /repo .js to search for all .js files in the /repo directory.
Tip: Separate your search with spaces e.g. /ssh pom.xml to search for src/ssh/pom.xml.
Tip: Use ↑ and ↓ arrow keys to navigate and return to view the file.
Tip: You can also navigate files with Ctrl+j (next) and Ctrl+k (previous) and view the file with Ctrl+o.
Tip: You can also navigate files with Alt+j (next) and Alt+k (previous) and view the file with Alt+o.