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//
// btDeformableBodySolver.cpp
// BulletSoftBody
//
// Created by Xuchen Han on 7/9/19.
//
#include <stdio.h>
#include "btDeformableBodySolver.h"
void btDeformableBodySolver::postStabilize()
{
for (int i = 0; i < m_softBodySet.size(); ++i)
{
btSoftBody* psb = m_softBodySet[i];
btMultiBodyJacobianData jacobianData;
const btScalar mrg = psb->getCollisionShape()->getMargin();
for (int j = 0; j < psb->m_rcontacts.size(); ++j)
{
const btSoftBody::RContact& c = psb->m_rcontacts[j];
// skip anchor points
if (c.m_node->m_im == 0)
continue;
const btSoftBody::sCti& cti = c.m_cti;
if (cti.m_colObj->hasContactResponse())
{
btVector3 va(0, 0, 0);
btRigidBody* rigidCol = 0;
btMultiBodyLinkCollider* multibodyLinkCol = 0;
btScalar* deltaV;
// grab the velocity of the rigid body
if (cti.m_colObj->getInternalType() == btCollisionObject::CO_RIGID_BODY)
{
rigidCol = (btRigidBody*)btRigidBody::upcast(cti.m_colObj);
va = rigidCol ? (rigidCol->getVelocityInLocalPoint(c.m_c1)) * m_dt : btVector3(0, 0, 0);
}
else if (cti.m_colObj->getInternalType() == btCollisionObject::CO_FEATHERSTONE_LINK)
{
multibodyLinkCol = (btMultiBodyLinkCollider*)btMultiBodyLinkCollider::upcast(cti.m_colObj);
if (multibodyLinkCol)
{
const int ndof = multibodyLinkCol->m_multiBody->getNumDofs() + 6;
jacobianData.m_jacobians.resize(ndof);
jacobianData.m_deltaVelocitiesUnitImpulse.resize(ndof);
btScalar* jac = &jacobianData.m_jacobians[0];
multibodyLinkCol->m_multiBody->fillContactJacobianMultiDof(multibodyLinkCol->m_link, c.m_node->m_x, cti.m_normal, jac, jacobianData.scratch_r, jacobianData.scratch_v, jacobianData.scratch_m);
deltaV = &jacobianData.m_deltaVelocitiesUnitImpulse[0];
multibodyLinkCol->m_multiBody->calcAccelerationDeltasMultiDof(&jacobianData.m_jacobians[0], deltaV, jacobianData.scratch_r, jacobianData.scratch_v);
btScalar vel = 0.0;
for (int j = 0; j < ndof; ++j)
{
vel += multibodyLinkCol->m_multiBody->getVelocityVector()[j] * jac[j];
}
va = cti.m_normal * vel * m_dt;
}
}
const btVector3 vb = c.m_node->m_v * m_dt;
const btVector3 vr = vb - va;
const btScalar dn = btDot(vr, cti.m_normal);
const btScalar dp = btMin((btDot(c.m_node->m_x, cti.m_normal) + cti.m_offset), mrg);
// c0 is the impulse matrix, c3 is 1 - the friction coefficient or 0, c4 is the contact hardness coefficient
btScalar dvn = dn * c.m_c4;
const btVector3 impulse = c.m_c0 * ((cti.m_normal * (dn * c.m_c4)));
// TODO: only contact is considered here, add friction later
if (dp < 0)
{
c.m_node->m_x -= dp * cti.m_normal * c.m_c4;
////
// 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 = 0.5;
// multibodyLinkCol->m_multiBody->applyDeltaVeeMultiDof(deltaV, -impulse.length() * multiplier);
// }
// }
}
}
}
}
void btDeformableBodySolver::solveConstraints(float solverdt)
{
m_dt = solverdt;
bool nodeUpdated = updateNodes();
reinitialize(nodeUpdated);
backupVelocity();
postStabilize();
for (int i = 0; i < m_solveIterations; ++i)
{
m_objective->computeResidual(solverdt, m_residual);
m_objective->computeStep(m_dv, m_residual, solverdt);
updateVelocity();
}
advect(solverdt);
}
void btDeformableBodySolver::reinitialize(bool nodeUpdated)
{
if (nodeUpdated)
{
m_dv.resize(m_numNodes);
m_residual.resize(m_numNodes);
}
for (int i = 0; i < m_dv.size(); ++i)
{
m_dv[i].setZero();
m_residual[i].setZero();
}
m_objective->reinitialize(nodeUpdated);
// remove contact constraints with separating velocity
setConstraintDirections();
}
void btDeformableBodySolver::setConstraintDirections()
{
m_objective->setConstraintDirections();
}
void btDeformableBodySolver::setWorld(btDeformableRigidDynamicsWorld* world)
{
m_world = world;
m_objective->setWorld(world);
}
void btDeformableBodySolver::updateVelocity()
{
// serial implementation
int counter = 0;
for (int i = 0; i < m_softBodySet.size(); ++i)
{
btSoftBody* psb = m_softBodySet[i];
for (int j = 0; j < psb->m_nodes.size(); ++j)
{
// psb->m_nodes[j].m_v += m_dv[counter];
psb->m_nodes[j].m_v = m_backupVelocity[counter]+m_dv[counter];
++counter;
}
}
}
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