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
21
23{
24 static const btPolarDecomposition polar;
25 return polar.decompose(m, q, s);
26}
27
29{
30public:
34 {
35 }
36
38 {
39 }
40
41 virtual void addScaledForces(btScalar scale, TVStack& force)
42 {
44 }
45
47 {
49 }
50
52 {
53 }
54
56 {
57 int numNodes = getNumNodes();
58 btAssert(numNodes <= force.size());
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 {
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
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;
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
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 {
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
109 {
110 }
111
113 {
114 }
115
117
119 {
120 return BT_COROTATED_FORCE;
121 }
122};
123
124#endif /* btCorotated_h */
static int PolarDecomposition(const btMatrix3x3 &m, btMatrix3x3 &q, btMatrix3x3 &s)
btDeformableLagrangianForceType
const T & btMax(const T &a, const T &b)
Definition btMinMax.h:27
float btScalar
The btScalar type abstracts floating point numbers, to easily switch between double and single floati...
Definition btScalar.h:314
#define SIMD_EPSILON
Definition btScalar.h:543
#define btAssert(x)
Definition btScalar.h:153
The btAlignedObjectArray template class uses a subset of the stl::vector interface for its methods It...
int size() const
return the number of elements in the array
virtual void addScaledElasticForce(btScalar scale, TVStack &force)
virtual void buildDampingForceDifferentialDiagonal(btScalar scale, TVStack &diagA)
virtual void addScaledDampingForceDifferential(btScalar scale, const TVStack &dv, TVStack &df)
virtual btDeformableLagrangianForceType getForceType()
virtual void addScaledDampingForce(btScalar scale, TVStack &force)
btAlignedObjectArray< btVector3 > TVStack
virtual void addScaledForces(btScalar scale, TVStack &force)
void firstPiola(const btMatrix3x3 &F, btMatrix3x3 &P)
virtual void addScaledElasticForceDifferential(btScalar scale, const TVStack &dx, TVStack &df)
virtual void addScaledExplicitForce(btScalar scale, TVStack &force)
btDeformableCorotatedForce(btScalar mu, btScalar lambda)
btAlignedObjectArray< btSoftBody * > m_softBodies
The btMatrix3x3 class implements a 3x3 rotation matrix, to perform linear algebra in combination with...
Definition btMatrix3x3.h:50
btMatrix3x3 transpose() const
Return the transpose of the matrix.
void setIdentity()
Set the matrix to the identity.
This class is used to compute the polar decomposition of a matrix.
unsigned int decompose(const btMatrix3x3 &a, btMatrix3x3 &u, btMatrix3x3 &h) const
Decomposes a matrix into orthogonal and symmetric, positive-definite parts.
The btSoftBody is an class to simulate cloth and volumetric soft bodies.
Definition btSoftBody.h:75
tTetraArray m_tetras
Definition btSoftBody.h:819
btVector3 can be used to represent 3D points and vectors.
Definition btVector3.h:82