128 lines
4.6 KiB
C++
128 lines
4.6 KiB
C++
/*
|
|
Written by Xuchen Han <xuchenhan2015@u.northwestern.edu>
|
|
|
|
Bullet Continuous Collision Detection and Physics Library
|
|
Copyright (c) 2019 Google Inc. http://bulletphysics.org
|
|
This software is provided 'as-is', without any express or implied warranty.
|
|
In no event will the authors be held liable for any damages arising from the use of this software.
|
|
Permission is granted to anyone to use this software for any purpose,
|
|
including commercial applications, and to alter it and redistribute it freely,
|
|
subject to the following restrictions:
|
|
1. The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required.
|
|
2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
|
|
3. This notice may not be removed or altered from any source distribution.
|
|
*/
|
|
|
|
#ifndef BT_COROTATED_H
|
|
#define BT_COROTATED_H
|
|
|
|
#include "btDeformableLagrangianForce.h"
|
|
#include "LinearMath/btPolarDecomposition.h"
|
|
|
|
static inline int PolarDecomposition(const btMatrix3x3& m, btMatrix3x3& q, btMatrix3x3& s)
|
|
{
|
|
static const btPolarDecomposition polar;
|
|
return polar.decompose(m, q, s);
|
|
}
|
|
|
|
class btDeformableCorotatedForce : public btDeformableLagrangianForce
|
|
{
|
|
public:
|
|
typedef btAlignedObjectArray<btVector3> TVStack;
|
|
btScalar m_mu, m_lambda;
|
|
btDeformableCorotatedForce(): m_mu(1), m_lambda(1)
|
|
{
|
|
|
|
}
|
|
|
|
btDeformableCorotatedForce(btScalar mu, btScalar lambda): m_mu(mu), m_lambda(lambda)
|
|
{
|
|
}
|
|
|
|
virtual void addScaledForces(btScalar scale, TVStack& force)
|
|
{
|
|
addScaledElasticForce(scale, force);
|
|
}
|
|
|
|
virtual void addScaledExplicitForce(btScalar scale, TVStack& force)
|
|
{
|
|
addScaledElasticForce(scale, force);
|
|
}
|
|
|
|
virtual void addScaledDampingForce(btScalar scale, TVStack& force)
|
|
{
|
|
}
|
|
|
|
virtual void addScaledElasticForce(btScalar scale, TVStack& force)
|
|
{
|
|
int numNodes = getNumNodes();
|
|
btAssert(numNodes <= force.size());
|
|
btVector3 grad_N_hat_1st_col = btVector3(-1,-1,-1);
|
|
for (int i = 0; i < m_softBodies.size(); ++i)
|
|
{
|
|
btSoftBody* psb = m_softBodies[i];
|
|
for (int j = 0; j < psb->m_tetras.size(); ++j)
|
|
{
|
|
btSoftBody::Tetra& tetra = psb->m_tetras[j];
|
|
btMatrix3x3 P;
|
|
firstPiola(tetra.m_F,P);
|
|
btVector3 force_on_node0 = P * (tetra.m_Dm_inverse.transpose()*grad_N_hat_1st_col);
|
|
btMatrix3x3 force_on_node123 = P * tetra.m_Dm_inverse.transpose();
|
|
|
|
btSoftBody::Node* node0 = tetra.m_n[0];
|
|
btSoftBody::Node* node1 = tetra.m_n[1];
|
|
btSoftBody::Node* node2 = tetra.m_n[2];
|
|
btSoftBody::Node* node3 = tetra.m_n[3];
|
|
size_t id0 = node0->index;
|
|
size_t id1 = node1->index;
|
|
size_t id2 = node2->index;
|
|
size_t id3 = node3->index;
|
|
|
|
// elastic force
|
|
// explicit elastic force
|
|
btScalar scale1 = scale * tetra.m_element_measure;
|
|
force[id0] -= scale1 * force_on_node0;
|
|
force[id1] -= scale1 * force_on_node123.getColumn(0);
|
|
force[id2] -= scale1 * force_on_node123.getColumn(1);
|
|
force[id3] -= scale1 * force_on_node123.getColumn(2);
|
|
}
|
|
}
|
|
}
|
|
|
|
void firstPiola(const btMatrix3x3& F, btMatrix3x3& P)
|
|
{
|
|
// btMatrix3x3 JFinvT = F.adjoint();
|
|
btScalar J = F.determinant();
|
|
P = F.adjoint().transpose() * (m_lambda * (J-1));
|
|
if (m_mu > SIMD_EPSILON)
|
|
{
|
|
btMatrix3x3 R,S;
|
|
if (J < 1024 * SIMD_EPSILON)
|
|
R.setIdentity();
|
|
else
|
|
PolarDecomposition(F, R, S); // this QR is not robust, consider using implicit shift svd
|
|
/*https://fuchuyuan.github.io/research/svd/paper.pdf*/
|
|
P += (F-R) * 2 * m_mu;
|
|
}
|
|
}
|
|
|
|
virtual void addScaledElasticForceDifferential(btScalar scale, const TVStack& dx, TVStack& df)
|
|
{
|
|
}
|
|
|
|
virtual void addScaledDampingForceDifferential(btScalar scale, const TVStack& dv, TVStack& df)
|
|
{
|
|
}
|
|
|
|
virtual void buildDampingForceDifferentialDiagonal(btScalar scale, TVStack& diagA){}
|
|
|
|
virtual btDeformableLagrangianForceType getForceType()
|
|
{
|
|
return BT_COROTATED_FORCE;
|
|
}
|
|
|
|
};
|
|
|
|
|
|
#endif /* btCorotated_h */
|