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//
// btDeformableBackwardEulerObjective.h
// BulletSoftBody
//
// Created by Xuchen Han on 7/1/19.
//
#ifndef BT_BACKWARD_EULER_OBJECTIVE_H
#define BT_BACKWARD_EULER_OBJECTIVE_H
#include <functional>
#include "btConjugateGradient.h"
#include "btLagrangianForce.h"
#include "btMassSpring.h"
#include "btDeformableContactProjection.h"
#include "btPreconditioner.h"
#include "btDeformableRigidDynamicsWorld.h"
class btDeformableRigidDynamicsWorld;
class btDeformableBackwardEulerObjective
{
public:
using TVStack = btAlignedObjectArray<btVector3>;
btScalar m_dt;
btDeformableRigidDynamicsWorld* m_world;
btAlignedObjectArray<btLagrangianForce*> m_lf;
btAlignedObjectArray<btSoftBody *>& m_softBodies;
Preconditioner* m_preconditioner;
btDeformableContactProjection projection;
const TVStack& m_backupVelocity;
btDeformableBackwardEulerObjective(btAlignedObjectArray<btSoftBody *>& softBodies, const TVStack& backup_v);
virtual ~btDeformableBackwardEulerObjective() {}
void initialize(){}
// compute the rhs for CG solve, i.e, add the dt scaled implicit force to residual
void computeResidual(btScalar dt, TVStack& residual) const;
// add explicit force to the velocity
void applyExplicitForce(TVStack& force);
// apply force to velocity and optionally reset the force to zero
void applyForce(TVStack& force, bool setZero);
// compute the norm of the residual
btScalar computeNorm(const TVStack& residual) const;
// compute one step of the solve (there is only one solve if the system is linear)
void computeStep(TVStack& dv, const TVStack& residual, const btScalar& dt);
// perform A*x = b
void multiply(const TVStack& x, TVStack& b) const;
// set initial guess for CG solve
void initialGuess(TVStack& dv, const TVStack& residual);
// reset data structure
void reinitialize(bool nodeUpdated);
void setDt(btScalar dt);
// enforce constraints in CG solve
void enforceConstraint(TVStack& x)
{
projection.enforceConstraint(x);
updateVelocity(x);
}
// add dv to velocity
void updateVelocity(const TVStack& dv);
//set constraints as projections
void setConstraints()
{
projection.setConstraints();
}
// update the projections and project the residual
void project(TVStack& r)
{
projection.update();
// TODO rename
projection.project(r);
}
// perform precondition M^(-1) x = b
void precondition(const TVStack& x, TVStack& b)
{
m_preconditioner->operator()(x,b);
}
virtual void setWorld(btDeformableRigidDynamicsWorld* world)
{
m_world = world;
projection.setWorld(world);
}
};
#endif /* btBackwardEulerObjective_h */
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