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Support btMultiBody soft contact using ERP and CFM. Also support custom relaxation parameter to allow successive over relaxation.

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Added demos for rigid and multi body soft (compliant) contact.
Will also add simplified Hertz compliant contact, by dynamically modifying the ERP/CFM to mimic a non-linear spring.
Note that btManifoldPoint is growing too big, we need to implement proper contact constraints derived from btTypedConstraint.
This commit is contained in:
erwin coumans
2016-02-22 18:40:00 -08:00
parent a3154f7a56
commit 6c9bfce975
10 changed files with 435 additions and 19 deletions
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5
src/BulletCollision/NarrowPhaseCollision/btManifoldPoint.h
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@@ -39,6 +39,7 @@ enum btContactPointFlags
{
BT_CONTACT_FLAG_LATERAL_FRICTION_INITIALIZED=1,
BT_CONTACT_FLAG_HAS_CONTACT_CFM=2,
BT_CONTACT_FLAG_HAS_CONTACT_ERP=4,
};
/// ManifoldContactPoint collects and maintains persistent contactpoints.
@@ -55,6 +56,7 @@ class btManifoldPoint
m_contactMotion1(0.f),
m_contactMotion2(0.f),
m_contactCFM(0.f),
m_contactERP(0.f),
m_frictionCFM(0.f),
m_lifeTime(0)
{
@@ -78,6 +80,7 @@ class btManifoldPoint
m_contactMotion1(0.f),
m_contactMotion2(0.f),
m_contactCFM(0.f),
m_contactERP(0.f),
m_frictionCFM(0.f),
m_lifeTime(0)
{
@@ -114,6 +117,8 @@ class btManifoldPoint
btScalar m_contactMotion1;
btScalar m_contactMotion2;
btScalar m_contactCFM;
btScalar m_contactERP;
btScalar m_frictionCFM;
int m_lifeTime;//lifetime of the contactpoint in frames

8
src/BulletDynamics/ConstraintSolver/btSequentialImpulseConstraintSolver.cpp
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@@ -780,6 +780,7 @@ void btSequentialImpulseConstraintSolver::setupContactConstraint(btSolverConstra
btScalar cfm = (cp.m_contactPointFlags&BT_CONTACT_FLAG_HAS_CONTACT_CFM)?cp.m_contactCFM:infoGlobal.m_globalCfm;
cfm *= invTimeStep;
btScalar erp = (cp.m_contactPointFlags&BT_CONTACT_FLAG_HAS_CONTACT_ERP)?cp.m_contactERP:infoGlobal.m_erp2;
btVector3 torqueAxis0 = rel_pos1.cross(cp.m_normalWorldOnB);
solverConstraint.m_angularComponentA = rb0 ? rb0->getInvInertiaTensorWorld()*torqueAxis0*rb0->getAngularFactor() : btVector3(0,0,0);
@@ -888,12 +889,7 @@ void btSequentialImpulseConstraintSolver::setupContactConstraint(btSolverConstra
btScalar velocityError = restitution - rel_vel;// * damping;
btScalar erp = infoGlobal.m_erp2;
if (!infoGlobal.m_splitImpulse || (penetration > infoGlobal.m_splitImpulsePenetrationThreshold))
{
erp = infoGlobal.m_erp;
}
if (penetration>0)
{
positionalError = 0;

23
src/BulletDynamics/Featherstone/btMultiBodyConstraintSolver.cpp
View File

@@ -221,9 +221,15 @@ void btMultiBodyConstraintSolver::setupMultiBodyContactConstraint(btMultiBodySol
if (bodyB)
rel_pos2 = pos2 - bodyB->getWorldTransform().getOrigin();
relaxation = 1.f;
relaxation = infoGlobal.m_sor;
btScalar invTimeStep = btScalar(1)/infoGlobal.m_timeStep;
btScalar cfm = (cp.m_contactPointFlags&BT_CONTACT_FLAG_HAS_CONTACT_CFM)?cp.m_contactCFM:infoGlobal.m_globalCfm;
cfm *= invTimeStep;
btScalar erp = (cp.m_contactPointFlags&BT_CONTACT_FLAG_HAS_CONTACT_ERP)?cp.m_contactERP:infoGlobal.m_erp2;
if (multiBodyA)
@@ -366,7 +372,7 @@ void btMultiBodyConstraintSolver::setupMultiBodyContactConstraint(btMultiBodySol
btScalar d = denom0+denom1;
btScalar d = denom0+denom1+cfm;
if (d>SIMD_EPSILON)
{
solverConstraint.m_jacDiagABInv = relaxation/(d);
@@ -477,12 +483,6 @@ void btMultiBodyConstraintSolver::setupMultiBodyContactConstraint(btMultiBodySol
btScalar positionalError = 0.f;
btScalar velocityError = restitution - rel_vel;// * damping; //note for friction restitution is always set to 0 (check above) so it is acutally velocityError = -rel_vel for friction
btScalar erp = infoGlobal.m_erp2;
if (!infoGlobal.m_splitImpulse || (penetration > infoGlobal.m_splitImpulsePenetrationThreshold))
{
erp = infoGlobal.m_erp;
}
if (penetration>0)
{
positionalError = 0;
@@ -522,7 +522,10 @@ void btMultiBodyConstraintSolver::setupMultiBodyContactConstraint(btMultiBodySol
solverConstraint.m_upperLimit = solverConstraint.m_friction;
}
solverConstraint.m_cfm = 0.f; //why not use cfmSlip?
solverConstraint.m_cfm = cfm*solverConstraint.m_jacDiagABInv;
}
}