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