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combat friction drift in positionCorrect by changing velocity and change it back (effectively only changing position)

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This commit is contained in:
Xuchen Han
2019-07-23 12:15:23 -07:00
parent a90cad2a96
commit 243b9fc8c7
15 changed files with 291 additions and 152 deletions
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91
src/BulletSoftBody/btDeformableContactProjection.cpp
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@@ -143,6 +143,8 @@ void btDeformableContactProjection::update()
friction.m_direction[j] = -local_tangent_dir;
// do not allow switching from static friction to dynamic friction
// it causes cg to explode
btScalar comp1 = -accumulated_normal*c->m_c3;
btScalar comp2 = tangent_norm;
if (-accumulated_normal*c->m_c3 < tangent_norm && friction.m_static_prev[j] == false && friction.m_released[j] == false)
{
friction.m_static[j] = false;
@@ -167,49 +169,44 @@ void btDeformableContactProjection::update()
// the incremental impulse applied to rb in the tangential direction
btVector3 incremental_tangent = (friction.m_impulse_prev[j] * friction.m_direction_prev[j])-(friction.m_impulse[j] * friction.m_direction[j]);
// TODO cleanup
if (1) // in the same CG solve, the set of constraits doesn't change
{
// c0 is the impulse matrix, c3 is 1 - the friction coefficient or 0, c4 is the contact hardness coefficient
// dv = new_impulse + accumulated velocity change in previous CG iterations
// so we have the invariant node->m_v = backupVelocity + dv;
btScalar dvn = -accumulated_normal * c->m_c2/m_dt;
// dv = new_impulse + accumulated velocity change in previous CG iterations
// so we have the invariant node->m_v = backupVelocity + dv;
btScalar dvn = -accumulated_normal * c->m_c2/m_dt;
// the following is equivalent
/*
btVector3 dv = -impulse_normal * c->m_c2/m_dt + c->m_node->m_v - backupVelocity[m_indices[c->m_node]];
btScalar dvn = dv.dot(cti.m_normal);
*/
constraint.m_value[j] = dvn;
// the incremental impulse:
// in the normal direction it's the normal component of "impulse"
// in the tangent direction it's the difference between the frictional impulse in the iteration and the previous iteration
impulse = impulse_normal + incremental_tangent;
if (cti.m_colObj->getInternalType() == btCollisionObject::CO_RIGID_BODY)
{
if (rigidCol)
rigidCol->applyImpulse(impulse, c->m_c1);
}
else if (cti.m_colObj->getInternalType() == btCollisionObject::CO_FEATHERSTONE_LINK)
{
// the following is equivalent
/*
btVector3 dv = -impulse_normal * c->m_c2/m_dt + c->m_node->m_v - backupVelocity[m_indices[c->m_node]];
btScalar dvn = dv.dot(cti.m_normal);
*/
constraint.m_value[j] = dvn;
// the incremental impulse:
// in the normal direction it's the normal component of "impulse"
// in the tangent direction it's the difference between the frictional impulse in the iteration and the previous iteration
impulse = impulse_normal + incremental_tangent;
if (cti.m_colObj->getInternalType() == btCollisionObject::CO_RIGID_BODY)
{
if (rigidCol)
rigidCol->applyImpulse(impulse, c->m_c1);
}
else if (cti.m_colObj->getInternalType() == btCollisionObject::CO_FEATHERSTONE_LINK)
if (multibodyLinkCol)
{
double multiplier = 1;
multibodyLinkCol->m_multiBody->applyDeltaVeeMultiDof(deltaV_normal, -impulse_normal.length() * multiplier);
if (multibodyLinkCol)
if (incremental_tangent.norm() > SIMD_EPSILON)
{
double multiplier = 1;
multibodyLinkCol->m_multiBody->applyDeltaVeeMultiDof(deltaV_normal, -impulse_normal.length() * multiplier);
if (incremental_tangent.norm() > SIMD_EPSILON)
{
btMultiBodyJacobianData jacobian_tangent;
btVector3 tangent = incremental_tangent.normalized();
findJacobian(multibodyLinkCol, jacobian_tangent, c->m_node->m_x, tangent);
const btScalar* deltaV_tangent = &jacobian_tangent.m_deltaVelocitiesUnitImpulse[0];
multibodyLinkCol->m_multiBody->applyDeltaVeeMultiDof(deltaV_tangent, incremental_tangent.length() * multiplier);
}
btMultiBodyJacobianData jacobian_tangent;
btVector3 tangent = incremental_tangent.normalized();
findJacobian(multibodyLinkCol, jacobian_tangent, c->m_node->m_x, tangent);
const btScalar* deltaV_tangent = &jacobian_tangent.m_deltaVelocitiesUnitImpulse[0];
multibodyLinkCol->m_multiBody->applyDeltaVeeMultiDof(deltaV_tangent, incremental_tangent.length() * multiplier);
}
}
}
@@ -404,14 +401,10 @@ void btDeformableContactProjection::enforceConstraint(TVStack& x)
const DeformableFrictionConstraint& friction= frictions[f];
for (int j = 0; j < friction.m_direction.size(); ++j)
{
// clear the old constraint
if (friction.m_static_prev[j] == true)
{
x[i] -= friction.m_direction_prev[j] * friction.m_dv_prev[j];
}
// add the new constraint
// add the friction constraint
if (friction.m_static[j] == true)
{
x[i] -= x[i].dot(friction.m_direction[j]) * friction.m_direction[j];
x[i] += friction.m_direction[j] * friction.m_dv[j];
}
}
@@ -467,9 +460,15 @@ void btDeformableContactProjection::project(TVStack& x)
}
// only add to the rhs if there is no static friction constraint on the node
if (friction.m_static[j] == false && !has_static_constraint)
if (friction.m_static[j] == false)
{
x[i] += friction.m_direction[j] * friction.m_impulse[j];
if (!has_static_constraint)
x[i] += friction.m_direction[j] * friction.m_impulse[j];
}
else
{
// otherwise clear the constraint in the friction direction
x[i] -= x[i].dot(friction.m_direction[j]) * friction.m_direction[j];
}
}
}