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

Bullet Collision Detection & Physics Library

btDeformableMassSpringForce.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_MASS_SPRING_H
17 #define BT_MASS_SPRING_H
18
19 #include "btDeformableLagrangianForce.h"
20
21 class btDeformableMassSpringForce : public btDeformableLagrangianForce
22 {
23 // If true, the damping force will be in the direction of the spring
24 // If false, the damping force will be in the direction of the velocity
25 bool m_momentum_conserving;
26 btScalar m_elasticStiffness, m_dampingStiffness, m_bendingStiffness;
27 public:
28 typedef btAlignedObjectArray<btVector3> TVStack;
29 btDeformableMassSpringForce() : m_momentum_conserving(false), m_elasticStiffness(1), m_dampingStiffness(0.05)
30 {
31 }
32 btDeformableMassSpringForce(btScalar k, btScalar d, bool conserve_angular = true, double bending_k = -1) : m_momentum_conserving(conserve_angular), m_elasticStiffness(k), m_dampingStiffness(d), m_bendingStiffness(bending_k)
33 {
34 if (m_bendingStiffness < btScalar(0))
35 {
36 m_bendingStiffness = m_elasticStiffness;
37 }
38 }
39
40 virtual void addScaledForces(btScalar scale, TVStack& force)
41 {
42 addScaledDampingForce(scale, force);
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 int numNodes = getNumNodes();
54 btAssert(numNodes <= force.size());
55 for (int i = 0; i < m_softBodies.size(); ++i)
56 {
57 const btSoftBody* psb = m_softBodies[i];
58 if (!psb->isActive())
59 {
60 continue;
61 }
62 for (int j = 0; j < psb->m_links.size(); ++j)
63 {
64 const btSoftBody::Link& link = psb->m_links[j];
65 btSoftBody::Node* node1 = link.m_n[0];
66 btSoftBody::Node* node2 = link.m_n[1];
67 size_t id1 = node1->index;
68 size_t id2 = node2->index;
69
70 // damping force
71 btVector3 v_diff = (node2->m_v - node1->m_v);
72 btVector3 scaled_force = scale * m_dampingStiffness * v_diff;
73 if (m_momentum_conserving)
74 {
75 if ((node2->m_x - node1->m_x).norm() > SIMD_EPSILON)
76 {
77 btVector3 dir = (node2->m_x - node1->m_x).normalized();
78 scaled_force = scale * m_dampingStiffness * v_diff.dot(dir) * dir;
79 }
80 }
81 force[id1] += scaled_force;
82 force[id2] -= scaled_force;
83 }
84 }
85 }
86
87 virtual void addScaledElasticForce(btScalar scale, TVStack& force)
88 {
89 int numNodes = getNumNodes();
90 btAssert(numNodes <= force.size());
91 for (int i = 0; i < m_softBodies.size(); ++i)
92 {
93 const btSoftBody* psb = m_softBodies[i];
94 if (!psb->isActive())
95 {
96 continue;
97 }
98 for (int j = 0; j < psb->m_links.size(); ++j)
99 {
100 const btSoftBody::Link& link = psb->m_links[j];
101 btSoftBody::Node* node1 = link.m_n[0];
102 btSoftBody::Node* node2 = link.m_n[1];
103 btScalar r = link.m_rl;
104 size_t id1 = node1->index;
105 size_t id2 = node2->index;
106
107 // elastic force
108 btVector3 dir = (node2->m_q - node1->m_q);
109 btVector3 dir_normalized = (dir.norm() > SIMD_EPSILON) ? dir.normalized() : btVector3(0,0,0);
110 btScalar scaled_stiffness = scale * (link.m_bbending ? m_bendingStiffness : m_elasticStiffness);
111 btVector3 scaled_force = scaled_stiffness * (dir - dir_normalized * r);
112 force[id1] += scaled_force;
113 force[id2] -= scaled_force;
114 }
115 }
116 }
117
118 virtual void addScaledDampingForceDifferential(btScalar scale, const TVStack& dv, TVStack& df)
119 {
120 // implicit damping force differential
121 for (int i = 0; i < m_softBodies.size(); ++i)
122 {
123 btSoftBody* psb = m_softBodies[i];
124 if (!psb->isActive())
125 {
126 continue;
127 }
128 btScalar scaled_k_damp = m_dampingStiffness * scale;
129 for (int j = 0; j < psb->m_links.size(); ++j)
130 {
131 const btSoftBody::Link& link = psb->m_links[j];
132 btSoftBody::Node* node1 = link.m_n[0];
133 btSoftBody::Node* node2 = link.m_n[1];
134 size_t id1 = node1->index;
135 size_t id2 = node2->index;
136
137 btVector3 local_scaled_df = scaled_k_damp * (dv[id2] - dv[id1]);
138 if (m_momentum_conserving)
139 {
140 if ((node2->m_x - node1->m_x).norm() > SIMD_EPSILON)
141 {
142 btVector3 dir = (node2->m_x - node1->m_x).normalized();
143 local_scaled_df= scaled_k_damp * (dv[id2] - dv[id1]).dot(dir) * dir;
144 }
145 }
146 df[id1] += local_scaled_df;
147 df[id2] -= local_scaled_df;
148 }
149 }
150 }
151
152 virtual double totalElasticEnergy(btScalar dt)
153 {
154 double energy = 0;
155 for (int i = 0; i < m_softBodies.size(); ++i)
156 {
157 const btSoftBody* psb = m_softBodies[i];
158 if (!psb->isActive())
159 {
160 continue;
161 }
162 for (int j = 0; j < psb->m_links.size(); ++j)
163 {
164 const btSoftBody::Link& link = psb->m_links[j];
165 btSoftBody::Node* node1 = link.m_n[0];
166 btSoftBody::Node* node2 = link.m_n[1];
167 btScalar r = link.m_rl;
168
169 // elastic force
170 btVector3 dir = (node2->m_q - node1->m_q);
171 energy += 0.5 * m_elasticStiffness * (dir.norm() - r) * (dir.norm() -r);
172 }
173 }
174 return energy;
175 }
176
177 virtual double totalDampingEnergy(btScalar dt)
178 {
179 double energy = 0;
180 int sz = 0;
181 for (int i = 0; i < m_softBodies.size(); ++i)
182 {
183 btSoftBody* psb = m_softBodies[i];
184 if (!psb->isActive())
185 {
186 continue;
187 }
188 for (int j = 0; j < psb->m_nodes.size(); ++j)
189 {
190 sz = btMax(sz, psb->m_nodes[j].index);
191 }
192 }
193 TVStack dampingForce;
194 dampingForce.resize(sz+1);
195 for (int i = 0; i < dampingForce.size(); ++i)
196 dampingForce[i].setZero();
197 addScaledDampingForce(0.5, dampingForce);
198 for (int i = 0; i < m_softBodies.size(); ++i)
199 {
200 btSoftBody* psb = m_softBodies[i];
201 for (int j = 0; j < psb->m_nodes.size(); ++j)
202 {
203 const btSoftBody::Node& node = psb->m_nodes[j];
204 energy -= dampingForce[node.index].dot(node.m_v) / dt;
205 }
206 }
207 return energy;
208 }
209
210 virtual void addScaledElasticForceDifferential(btScalar scale, const TVStack& dx, TVStack& df)
211 {
212 // implicit damping force differential
213 for (int i = 0; i < m_softBodies.size(); ++i)
214 {
215 const btSoftBody* psb = m_softBodies[i];
216 if (!psb->isActive())
217 {
218 continue;
219 }
220 for (int j = 0; j < psb->m_links.size(); ++j)
221 {
222 const btSoftBody::Link& link = psb->m_links[j];
223 btSoftBody::Node* node1 = link.m_n[0];
224 btSoftBody::Node* node2 = link.m_n[1];
225 size_t id1 = node1->index;
226 size_t id2 = node2->index;
227 btScalar r = link.m_rl;
228
229 btVector3 dir = (node1->m_q - node2->m_q);
230 btScalar dir_norm = dir.norm();
231 btVector3 dir_normalized = (dir_norm > SIMD_EPSILON) ? dir.normalized() : btVector3(0,0,0);
232 btVector3 dx_diff = dx[id1] - dx[id2];
233 btVector3 scaled_df = btVector3(0,0,0);
234 btScalar scaled_k = scale * (link.m_bbending ? m_bendingStiffness : m_elasticStiffness);
235 if (dir_norm > SIMD_EPSILON)
236 {
237 scaled_df -= scaled_k * dir_normalized.dot(dx_diff) * dir_normalized;
238 scaled_df += scaled_k * dir_normalized.dot(dx_diff) * ((dir_norm-r)/dir_norm) * dir_normalized;
239 scaled_df -= scaled_k * ((dir_norm-r)/dir_norm) * dx_diff;
240 }
241
242 df[id1] += scaled_df;
243 df[id2] -= scaled_df;
244 }
245 }
246 }
247
248 virtual btDeformableLagrangianForceType getForceType()
249 {
250 return BT_MASSSPRING_FORCE;
251 }
252
253 };
254
255 #endif /* btMassSpring_h */
SIMD_EPSILON
#define SIMD_EPSILON
Definition: btScalar.h:543
btDeformableMassSpringForce::addScaledForces
virtual void addScaledForces(btScalar scale, TVStack &force)
Definition: btDeformableMassSpringForce.h:40
btSoftBody::m_links
tLinkArray m_links
Definition: btSoftBody.h:779
dot
btScalar dot(const btQuaternion &q1, const btQuaternion &q2)
Calculate the dot product between two quaternions.
Definition: btQuaternion.h:888
btScalar
float btScalar
The btScalar type abstracts floating point numbers, to easily switch between double and single floati...
Definition: btScalar.h:314
btVector3::dot
btScalar dot(const btVector3 &v) const
Return the dot product.
Definition: btVector3.h:229
btDeformableMassSpringForce::addScaledElasticForceDifferential
virtual void addScaledElasticForceDifferential(btScalar scale, const TVStack &dx, TVStack &df)
Definition: btDeformableMassSpringForce.h:210
btSoftBody::Link::m_n
Node * m_n[2]
Definition: btSoftBody.h:275
BT_MASSSPRING_FORCE
@ BT_MASSSPRING_FORCE
Definition: btDeformableLagrangianForce.h:26
btDeformableMassSpringForce::addScaledDampingForceDifferential
virtual void addScaledDampingForceDifferential(btScalar scale, const TVStack &dv, TVStack &df)
Definition: btDeformableMassSpringForce.h:118
btSoftBody::Node
Definition: btSoftBody.h:256
btMax
const T & btMax(const T &a, const T &b)
Definition: btMinMax.h:27
btDeformableMassSpringForce::TVStack
btAlignedObjectArray< btVector3 > TVStack
Definition: btDeformableMassSpringForce.h:28
btSoftBody::Node::m_q
btVector3 m_q
Definition: btSoftBody.h:258
btDeformableMassSpringForce
Definition: btDeformableMassSpringForce.h:22
btAssert
#define btAssert(x)
Definition: btScalar.h:153
btSoftBody::Node::m_x
btVector3 m_x
Definition: btSoftBody.h:257
btDeformableLagrangianForce::m_softBodies
btAlignedObjectArray< btSoftBody * > m_softBodies
Definition: btDeformableLagrangianForce.h:41
btSoftBody::Link
Definition: btSoftBody.h:273
btAlignedObjectArray::resize
void resize(int newsize, const T &fillData=T())
Definition: btAlignedObjectArray.h:203
btDeformableMassSpringForce::m_momentum_conserving
bool m_momentum_conserving
Definition: btDeformableMassSpringForce.h:25
btDeformableLagrangianForce
Definition: btDeformableLagrangianForce.h:38
btDeformableMassSpringForce::btDeformableMassSpringForce
btDeformableMassSpringForce(btScalar k, btScalar d, bool conserve_angular=true, double bending_k=-1)
Definition: btDeformableMassSpringForce.h:32
btDeformableMassSpringForce::totalDampingEnergy
virtual double totalDampingEnergy(btScalar dt)
Definition: btDeformableMassSpringForce.h:177
btVector3
btVector3 can be used to represent 3D points and vectors.
Definition: btVector3.h:82
btDeformableMassSpringForce::addScaledElasticForce
virtual void addScaledElasticForce(btScalar scale, TVStack &force)
Definition: btDeformableMassSpringForce.h:87
btSoftBody::Node::index
int index
Definition: btSoftBody.h:268
btDeformableMassSpringForce::m_dampingStiffness
btScalar m_dampingStiffness
Definition: btDeformableMassSpringForce.h:26
btSoftBody::Link::m_rl
btScalar m_rl
Definition: btSoftBody.h:276
btAlignedObjectArray< btVector3 >
btDeformableMassSpringForce::m_bendingStiffness
btScalar m_bendingStiffness
Definition: btDeformableMassSpringForce.h:26
btDeformableMassSpringForce::addScaledDampingForce
virtual void addScaledDampingForce(btScalar scale, TVStack &force)
Definition: btDeformableMassSpringForce.h:51
btDeformableMassSpringForce::btDeformableMassSpringForce
btDeformableMassSpringForce()
Definition: btDeformableMassSpringForce.h:29
btSoftBody
The btSoftBody is an class to simulate cloth and volumetric soft bodies.
Definition: btSoftBody.h:73
btCollisionObject::isActive
bool isActive() const
Definition: btCollisionObject.h:294
btDeformableLagrangianForce::getNumNodes
virtual int getNumNodes()
Definition: btDeformableLagrangianForce.h:72
btSoftBody::Link::m_bbending
int m_bbending
Definition: btSoftBody.h:277
btDeformableLagrangianForceType
btDeformableLagrangianForceType
Definition: btDeformableLagrangianForce.h:24
btVector3::norm
btScalar norm() const
Return the norm (length) of the vector.
Definition: btVector3.h:263
btDeformableMassSpringForce::getForceType
virtual btDeformableLagrangianForceType getForceType()
Definition: btDeformableMassSpringForce.h:248
btDeformableMassSpringForce::totalElasticEnergy
virtual double totalElasticEnergy(btScalar dt)
Definition: btDeformableMassSpringForce.h:152
btDeformableLagrangianForce.h
btSoftBody::Node::m_v
btVector3 m_v
Definition: btSoftBody.h:259
btDeformableMassSpringForce::m_elasticStiffness
btScalar m_elasticStiffness
Definition: btDeformableMassSpringForce.h:26
btVector3::normalized
btVector3 normalized() const
Return a normalized version of this vector.
Definition: btVector3.h:949
btDeformableMassSpringForce::addScaledExplicitForce
virtual void addScaledExplicitForce(btScalar scale, TVStack &force)
Definition: btDeformableMassSpringForce.h:46
btAlignedObjectArray::size
int size() const
return the number of elements in the array
Definition: btAlignedObjectArray.h:142
btSoftBody::m_nodes
tNodeArray m_nodes
Definition: btSoftBody.h:777