Bullet Collision Detection & Physics Library: btDeformableCorotatedForce.h Source File

Bullet Collision Detection & Physics Library

btDeformableCorotatedForce.h
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1/*
2 Written by Xuchen Han <xuchenhan2015@u.northwestern.edu>
3
4 Bullet Continuous Collision Detection and Physics Library
5 Copyright (c) 2019 Google Inc. http://bulletphysics.org
6 This software is provided 'as-is', without any express or implied warranty.
7 In no event will the authors be held liable for any damages arising from the use of this software.
8 Permission is granted to anyone to use this software for any purpose,
9 including commercial applications, and to alter it and redistribute it freely,
10 subject to the following restrictions:
11 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.
12 2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
13 3. This notice may not be removed or altered from any source distribution.
14 */
15
16#ifndef BT_COROTATED_H
17#define BT_COROTATED_H
18
19#include "btDeformableLagrangianForce.h"
20#include "LinearMath/btPolarDecomposition.h"
21
22 static inline int PolarDecomposition(const btMatrix3x3& m, btMatrix3x3& q, btMatrix3x3& s)
23{
24 static const btPolarDecomposition polar;
25 return polar.decompose(m, q, s);
26}
27
28 class btDeformableCorotatedForce : public btDeformableLagrangianForce
29{
30public:
31 typedef btAlignedObjectArray<btVector3> TVStack;
32 btScalar m_mu, m_lambda;
33 btDeformableCorotatedForce() : m_mu(1), m_lambda(1)
34 {
35 }
36
37 btDeformableCorotatedForce(btScalar mu, btScalar lambda) : m_mu(mu), m_lambda(lambda)
38 {
39 }
40
41 virtual void addScaledForces(btScalar scale, TVStack& force)
42 {
43 addScaledElasticForce(scale, force);
44 }
45
46 virtual void addScaledExplicitForce(btScalar scale, TVStack& force)
47 {
48 addScaledElasticForce(scale, force);
49 }
50
51 virtual void addScaledDampingForce(btScalar scale, TVStack& force)
52 {
53 }
54
55 virtual void addScaledElasticForce(btScalar scale, TVStack& force)
56 {
57 int numNodes = getNumNodes();
58 btAssert(numNodes <= force.size());
59 btVector3 grad_N_hat_1st_col = btVector3(-1, -1, -1);
60 for (int i = 0; i < m_softBodies.size(); ++i)
61 {
62 btSoftBody* psb = m_softBodies[i];
63 for (int j = 0; j < psb->m_tetras.size(); ++j)
64 {
65 btSoftBody::Tetra& tetra = psb->m_tetras[j];
66 btMatrix3x3 P;
67 firstPiola(tetra.m_F, P);
68 btVector3 force_on_node0 = P * (tetra.m_Dm_inverse.transpose() * grad_N_hat_1st_col);
69 btMatrix3x3 force_on_node123 = P * tetra.m_Dm_inverse.transpose();
70
71 btSoftBody::Node* node0 = tetra.m_n[0];
72 btSoftBody::Node* node1 = tetra.m_n[1];
73 btSoftBody::Node* node2 = tetra.m_n[2];
74 btSoftBody::Node* node3 = tetra.m_n[3];
75 size_t id0 = node0->index;
76 size_t id1 = node1->index;
77 size_t id2 = node2->index;
78 size_t id3 = node3->index;
79
80 // elastic force
81 // explicit elastic force
82 btScalar scale1 = scale * tetra.m_element_measure;
83 force[id0] -= scale1 * force_on_node0;
84 force[id1] -= scale1 * force_on_node123.getColumn(0);
85 force[id2] -= scale1 * force_on_node123.getColumn(1);
86 force[id3] -= scale1 * force_on_node123.getColumn(2);
87 }
88 }
89 }
90
91 void firstPiola(const btMatrix3x3& F, btMatrix3x3& P)
92 {
93 // btMatrix3x3 JFinvT = F.adjoint();
94 btScalar J = F.determinant();
95 P = F.adjoint().transpose() * (m_lambda * (J - 1));
96 if (m_mu > SIMD_EPSILON)
97 {
98 btMatrix3x3 R, S;
99 if (J < 1024 * SIMD_EPSILON)
100 R.setIdentity();
101 else
102 PolarDecomposition(F, R, S); // this QR is not robust, consider using implicit shift svd
103 /*https://fuchuyuan.github.io/research/svd/paper.pdf*/
104 P += (F - R) * 2 * m_mu;
105 }
106 }
107
108 virtual void addScaledElasticForceDifferential(btScalar scale, const TVStack& dx, TVStack& df)
109 {
110 }
111
112 virtual void addScaledDampingForceDifferential(btScalar scale, const TVStack& dv, TVStack& df)
113 {
114 }
115
116 virtual void buildDampingForceDifferentialDiagonal(btScalar scale, TVStack& diagA) {}
117
118 virtual btDeformableLagrangianForceType getForceType()
119 {
120 return BT_COROTATED_FORCE;
121 }
122};
123
124#endif /* btCorotated_h */
PolarDecomposition
static int PolarDecomposition(const btMatrix3x3 &m, btMatrix3x3 &q, btMatrix3x3 &s)
Definition btDeformableCorotatedForce.h:22
btDeformableLagrangianForce.h
btDeformableLagrangianForceType
btDeformableLagrangianForceType
Definition btDeformableLagrangianForce.h:24
BT_COROTATED_FORCE
@ BT_COROTATED_FORCE
Definition btDeformableLagrangianForce.h:27
btPolarDecomposition.h
btScalar
float btScalar
The btScalar type abstracts floating point numbers, to easily switch between double and single floati...
Definition btScalar.h:314
SIMD_EPSILON
#define SIMD_EPSILON
Definition btScalar.h:543
btAssert
#define btAssert(x)
Definition btScalar.h:153
btAlignedObjectArray
The btAlignedObjectArray template class uses a subset of the stl::vector interface for its methods It...
Definition btAlignedObjectArray.h:46
btAlignedObjectArray::size
int size() const
return the number of elements in the array
Definition btAlignedObjectArray.h:142
btDeformableCorotatedForce::addScaledElasticForce
virtual void addScaledElasticForce(btScalar scale, TVStack &force)
Definition btDeformableCorotatedForce.h:55
btDeformableCorotatedForce::buildDampingForceDifferentialDiagonal
virtual void buildDampingForceDifferentialDiagonal(btScalar scale, TVStack &diagA)
Definition btDeformableCorotatedForce.h:116
btDeformableCorotatedForce::addScaledDampingForceDifferential
virtual void addScaledDampingForceDifferential(btScalar scale, const TVStack &dv, TVStack &df)
Definition btDeformableCorotatedForce.h:112
btDeformableCorotatedForce::getForceType
virtual btDeformableLagrangianForceType getForceType()
Definition btDeformableCorotatedForce.h:118
btDeformableCorotatedForce::addScaledDampingForce
virtual void addScaledDampingForce(btScalar scale, TVStack &force)
Definition btDeformableCorotatedForce.h:51
btDeformableCorotatedForce::m_lambda
btScalar m_lambda
Definition btDeformableCorotatedForce.h:32
btDeformableCorotatedForce::btDeformableCorotatedForce
btDeformableCorotatedForce()
Definition btDeformableCorotatedForce.h:33
btDeformableCorotatedForce::TVStack
btAlignedObjectArray< btVector3 > TVStack
Definition btDeformableCorotatedForce.h:31
btDeformableCorotatedForce::addScaledForces
virtual void addScaledForces(btScalar scale, TVStack &force)
Definition btDeformableCorotatedForce.h:41
btDeformableCorotatedForce::m_mu
btScalar m_mu
Definition btDeformableCorotatedForce.h:32
btDeformableCorotatedForce::firstPiola
void firstPiola(const btMatrix3x3 &F, btMatrix3x3 &P)
Definition btDeformableCorotatedForce.h:91
btDeformableCorotatedForce::addScaledElasticForceDifferential
virtual void addScaledElasticForceDifferential(btScalar scale, const TVStack &dx, TVStack &df)
Definition btDeformableCorotatedForce.h:108
btDeformableCorotatedForce::addScaledExplicitForce
virtual void addScaledExplicitForce(btScalar scale, TVStack &force)
Definition btDeformableCorotatedForce.h:46
btDeformableCorotatedForce::btDeformableCorotatedForce
btDeformableCorotatedForce(btScalar mu, btScalar lambda)
Definition btDeformableCorotatedForce.h:37
btDeformableLagrangianForce::getNumNodes
virtual int getNumNodes()
Definition btDeformableLagrangianForce.h:78
btDeformableLagrangianForce::btDeformableLagrangianForce
btDeformableLagrangianForce()
Definition btDeformableLagrangianForce.h:45
btDeformableLagrangianForce::m_softBodies
btAlignedObjectArray< btSoftBody * > m_softBodies
Definition btDeformableLagrangianForce.h:42
btMatrix3x3
The btMatrix3x3 class implements a 3x3 rotation matrix, to perform linear algebra in combination with...
Definition btMatrix3x3.h:50
btMatrix3x3::adjoint
btMatrix3x3 adjoint() const
Return the adjoint of the matrix.
Definition btMatrix3x3.h:1085
btMatrix3x3::transpose
btMatrix3x3 transpose() const
Return the transpose of the matrix.
Definition btMatrix3x3.h:1049
btMatrix3x3::setIdentity
void setIdentity()
Set the matrix to the identity.
Definition btMatrix3x3.h:323
btMatrix3x3::determinant
btScalar determinant() const
Return the determinant of the matrix.
Definition btMatrix3x3.h:1022
btMatrix3x3::getColumn
btVector3 getColumn(int i) const
Get a column of the matrix as a vector.
Definition btMatrix3x3.h:142
btPolarDecomposition
This class is used to compute the polar decomposition of a matrix.
Definition btPolarDecomposition.h:15
btPolarDecomposition::decompose
unsigned int decompose(const btMatrix3x3 &a, btMatrix3x3 &u, btMatrix3x3 &h) const
Decomposes a matrix into orthogonal and symmetric, positive-definite parts.
Definition btPolarDecomposition.cpp:38
btSoftBody
The btSoftBody is an class to simulate cloth and volumetric soft bodies.
Definition btSoftBody.h:75
btSoftBody::m_tetras
tTetraArray m_tetras
Definition btSoftBody.h:819
btVector3
btVector3 can be used to represent 3D points and vectors.
Definition btVector3.h:82
btSoftBody::Node
Definition btSoftBody.h:268
btSoftBody::Node::index
int index
Definition btSoftBody.h:280
btSoftBody::Tetra
Definition btSoftBody.h:317
btSoftBody::Tetra::m_element_measure
btScalar m_element_measure
Definition btSoftBody.h:326
btSoftBody::Tetra::m_Dm_inverse
btMatrix3x3 m_Dm_inverse
Definition btSoftBody.h:324
btSoftBody::Tetra::m_F
btMatrix3x3 m_F
Definition btSoftBody.h:325
btSoftBody::Tetra::m_n
Node * m_n[4]
Definition btSoftBody.h:318