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fix issue with btMultiBody friction in combination with soft contacts (friction should not re-use normal contact cfm/erp)

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implement friction anchors, position friction correction, disabled by default. Use colObj->setCollisionFlag(flag | CF_HAS_FRICTION_ANCHOR); See test/RobotClientAPI/SlopeFrictionMain.cpp. In URDF or SDF, add <friction_anchor/> in <contact> section of <link> to enable.
PhysicsServer: properly restore old activation state after releasing picked object
btMultiBodyConstraintSolver: disable flip/flop of contact/friction constraint solving by default (it breaks some internal flaky unit tests)
This commit is contained in:
Erwin Coumans
2017-03-20 10:58:07 -07:00
parent 865d37fcb5
commit 0b017b0f53
18 changed files with 299 additions and 91 deletions
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1
src/BulletCollision/NarrowPhaseCollision/btManifoldPoint.h
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@@ -41,6 +41,7 @@ enum btContactPointFlags
BT_CONTACT_FLAG_HAS_CONTACT_CFM=2,
BT_CONTACT_FLAG_HAS_CONTACT_ERP=4,
BT_CONTACT_FLAG_CONTACT_STIFFNESS_DAMPING = 8,
BT_CONTACT_FLAG_FRICTION_ANCHOR = 16,
};
/// ManifoldContactPoint collects and maintains persistent contactpoints.

1
src/BulletCollision/NarrowPhaseCollision/btPersistentManifold.cpp
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@@ -279,6 +279,7 @@ void btPersistentManifold::refreshContactPoints(const btTransform& trA,const btT
removeContactPoint(i);
} else
{
//todo: friction anchor may require the contact to be around a bit longer
//contact also becomes invalid when relative movement orthogonal to normal exceeds margin
projectedPoint = manifoldPoint.m_positionWorldOnA - manifoldPoint.m_normalWorldOnB * manifoldPoint.m_distance1;
projectedDifference = manifoldPoint.m_positionWorldOnB - projectedPoint;

55
src/BulletCollision/NarrowPhaseCollision/btPersistentManifold.h
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@@ -172,39 +172,54 @@ public:
btAssert(m_pointCache[lastUsedIndex].m_userPersistentData==0);
m_cachedPoints--;
}
void replaceContactPoint(const btManifoldPoint& newPoint,int insertIndex)
void replaceContactPoint(const btManifoldPoint& newPoint, int insertIndex)
{
btAssert(validContactDistance(newPoint));
#define MAINTAIN_PERSISTENCY 1
#ifdef MAINTAIN_PERSISTENCY
int lifeTime = m_pointCache[insertIndex].getLifeTime();
btScalar appliedImpulse = m_pointCache[insertIndex].m_appliedImpulse;
btScalar appliedLateralImpulse1 = m_pointCache[insertIndex].m_appliedImpulseLateral1;
btScalar appliedLateralImpulse2 = m_pointCache[insertIndex].m_appliedImpulseLateral2;
// bool isLateralFrictionInitialized = m_pointCache[insertIndex].m_lateralFrictionInitialized;
btAssert(lifeTime>=0);
void* cache = m_pointCache[insertIndex].m_userPersistentData;
m_pointCache[insertIndex] = newPoint;
m_pointCache[insertIndex].m_userPersistentData = cache;
m_pointCache[insertIndex].m_appliedImpulse = appliedImpulse;
m_pointCache[insertIndex].m_appliedImpulseLateral1 = appliedLateralImpulse1;
m_pointCache[insertIndex].m_appliedImpulseLateral2 = appliedLateralImpulse2;
int lifeTime = m_pointCache[insertIndex].getLifeTime();
btScalar appliedImpulse = m_pointCache[insertIndex].m_appliedImpulse;
btScalar appliedLateralImpulse1 = m_pointCache[insertIndex].m_appliedImpulseLateral1;
btScalar appliedLateralImpulse2 = m_pointCache[insertIndex].m_appliedImpulseLateral2;
bool replacePoint = true;
///we keep existing contact points for friction anchors
///if the friction force is within the Coulomb friction cone
if (newPoint.m_contactPointFlags & BT_CONTACT_FLAG_FRICTION_ANCHOR)
{
// printf("appliedImpulse=%f\n", appliedImpulse);
// printf("appliedLateralImpulse1=%f\n", appliedLateralImpulse1);
// printf("appliedLateralImpulse2=%f\n", appliedLateralImpulse2);
// printf("mu = %f\n", m_pointCache[insertIndex].m_combinedFriction);
btScalar mu = m_pointCache[insertIndex].m_combinedFriction;
btScalar eps = 0; //we could allow to enlarge or shrink the tolerance to check against the friction cone a bit, say 1e-7
btScalar a = appliedLateralImpulse1 * appliedLateralImpulse1 + appliedLateralImpulse2 * appliedLateralImpulse2;
btScalar b = eps + mu * appliedImpulse;
b = b * b;
replacePoint = (a) > (b);
}
if (replacePoint)
{
btAssert(lifeTime >= 0);
void* cache = m_pointCache[insertIndex].m_userPersistentData;
m_pointCache[insertIndex] = newPoint;
m_pointCache[insertIndex].m_userPersistentData = cache;
m_pointCache[insertIndex].m_appliedImpulse = appliedImpulse;
m_pointCache[insertIndex].m_appliedImpulseLateral1 = appliedLateralImpulse1;
m_pointCache[insertIndex].m_appliedImpulseLateral2 = appliedLateralImpulse2;
}
m_pointCache[insertIndex].m_lifeTime = lifeTime;
#else
clearUserCache(m_pointCache[insertIndex]);
m_pointCache[insertIndex] = newPoint;
#endif
}
bool validContactDistance(const btManifoldPoint& pt) const
{
return pt.m_distance1 <= getContactBreakingThreshold();