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Diffstat (limited to 'extern/bullet2/src/BulletSoftBody/btDeformableMassSpringForce.h')
| -rw-r--r-- | extern/bullet2/src/BulletSoftBody/btDeformableMassSpringForce.h | 301 |
1 files changed, 301 insertions, 0 deletions
diff --git a/extern/bullet2/src/BulletSoftBody/btDeformableMassSpringForce.h b/extern/bullet2/src/BulletSoftBody/btDeformableMassSpringForce.h new file mode 100644 index 00000000000..8c97bd1ba8b --- /dev/null +++ b/extern/bullet2/src/BulletSoftBody/btDeformableMassSpringForce.h @@ -0,0 +1,301 @@ +/* + 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_MASS_SPRING_H +#define BT_MASS_SPRING_H + +#include "btDeformableLagrangianForce.h" + +class btDeformableMassSpringForce : public btDeformableLagrangianForce +{ + // If true, the damping force will be in the direction of the spring + // If false, the damping force will be in the direction of the velocity + bool m_momentum_conserving; + btScalar m_elasticStiffness, m_dampingStiffness, m_bendingStiffness; + +public: + typedef btAlignedObjectArray<btVector3> TVStack; + btDeformableMassSpringForce() : m_momentum_conserving(false), m_elasticStiffness(1), m_dampingStiffness(0.05) + { + } + 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) + { + if (m_bendingStiffness < btScalar(0)) + { + m_bendingStiffness = m_elasticStiffness; + } + } + + virtual void addScaledForces(btScalar scale, TVStack& force) + { + addScaledDampingForce(scale, force); + addScaledElasticForce(scale, force); + } + + virtual void addScaledExplicitForce(btScalar scale, TVStack& force) + { + addScaledElasticForce(scale, force); + } + + virtual void addScaledDampingForce(btScalar scale, TVStack& force) + { + int numNodes = getNumNodes(); + btAssert(numNodes <= force.size()); + for (int i = 0; i < m_softBodies.size(); ++i) + { + const btSoftBody* psb = m_softBodies[i]; + if (!psb->isActive()) + { + continue; + } + for (int j = 0; j < psb->m_links.size(); ++j) + { + const btSoftBody::Link& link = psb->m_links[j]; + btSoftBody::Node* node1 = link.m_n[0]; + btSoftBody::Node* node2 = link.m_n[1]; + size_t id1 = node1->index; + size_t id2 = node2->index; + + // damping force + btVector3 v_diff = (node2->m_v - node1->m_v); + btVector3 scaled_force = scale * m_dampingStiffness * v_diff; + if (m_momentum_conserving) + { + if ((node2->m_x - node1->m_x).norm() > SIMD_EPSILON) + { + btVector3 dir = (node2->m_x - node1->m_x).normalized(); + scaled_force = scale * m_dampingStiffness * v_diff.dot(dir) * dir; + } + } + force[id1] += scaled_force; + force[id2] -= scaled_force; + } + } + } + + virtual void addScaledElasticForce(btScalar scale, TVStack& force) + { + int numNodes = getNumNodes(); + btAssert(numNodes <= force.size()); + for (int i = 0; i < m_softBodies.size(); ++i) + { + const btSoftBody* psb = m_softBodies[i]; + if (!psb->isActive()) + { + continue; + } + for (int j = 0; j < psb->m_links.size(); ++j) + { + const btSoftBody::Link& link = psb->m_links[j]; + btSoftBody::Node* node1 = link.m_n[0]; + btSoftBody::Node* node2 = link.m_n[1]; + btScalar r = link.m_rl; + size_t id1 = node1->index; + size_t id2 = node2->index; + + // elastic force + btVector3 dir = (node2->m_q - node1->m_q); + btVector3 dir_normalized = (dir.norm() > SIMD_EPSILON) ? dir.normalized() : btVector3(0, 0, 0); + btScalar scaled_stiffness = scale * (link.m_bbending ? m_bendingStiffness : m_elasticStiffness); + btVector3 scaled_force = scaled_stiffness * (dir - dir_normalized * r); + force[id1] += scaled_force; + force[id2] -= scaled_force; + } + } + } + + virtual void addScaledDampingForceDifferential(btScalar scale, const TVStack& dv, TVStack& df) + { + // implicit damping force differential + for (int i = 0; i < m_softBodies.size(); ++i) + { + btSoftBody* psb = m_softBodies[i]; + if (!psb->isActive()) + { + continue; + } + btScalar scaled_k_damp = m_dampingStiffness * scale; + for (int j = 0; j < psb->m_links.size(); ++j) + { + const btSoftBody::Link& link = psb->m_links[j]; + btSoftBody::Node* node1 = link.m_n[0]; + btSoftBody::Node* node2 = link.m_n[1]; + size_t id1 = node1->index; + size_t id2 = node2->index; + + btVector3 local_scaled_df = scaled_k_damp * (dv[id2] - dv[id1]); + if (m_momentum_conserving) + { + if ((node2->m_x - node1->m_x).norm() > SIMD_EPSILON) + { + btVector3 dir = (node2->m_x - node1->m_x).normalized(); + local_scaled_df = scaled_k_damp * (dv[id2] - dv[id1]).dot(dir) * dir; + } + } + df[id1] += local_scaled_df; + df[id2] -= local_scaled_df; + } + } + } + + virtual void buildDampingForceDifferentialDiagonal(btScalar scale, TVStack& diagA) + { + // implicit damping force differential + for (int i = 0; i < m_softBodies.size(); ++i) + { + btSoftBody* psb = m_softBodies[i]; + if (!psb->isActive()) + { + continue; + } + btScalar scaled_k_damp = m_dampingStiffness * scale; + for (int j = 0; j < psb->m_links.size(); ++j) + { + const btSoftBody::Link& link = psb->m_links[j]; + btSoftBody::Node* node1 = link.m_n[0]; + btSoftBody::Node* node2 = link.m_n[1]; + size_t id1 = node1->index; + size_t id2 = node2->index; + if (m_momentum_conserving) + { + if ((node2->m_x - node1->m_x).norm() > SIMD_EPSILON) + { + btVector3 dir = (node2->m_x - node1->m_x).normalized(); + for (int d = 0; d < 3; ++d) + { + if (node1->m_im > 0) + diagA[id1][d] -= scaled_k_damp * dir[d] * dir[d]; + if (node2->m_im > 0) + diagA[id2][d] -= scaled_k_damp * dir[d] * dir[d]; + } + } + } + else + { + for (int d = 0; d < 3; ++d) + { + if (node1->m_im > 0) + diagA[id1][d] -= scaled_k_damp; + if (node2->m_im > 0) + diagA[id2][d] -= scaled_k_damp; + } + } + } + } + } + + virtual double totalElasticEnergy(btScalar dt) + { + double energy = 0; + for (int i = 0; i < m_softBodies.size(); ++i) + { + const btSoftBody* psb = m_softBodies[i]; + if (!psb->isActive()) + { + continue; + } + for (int j = 0; j < psb->m_links.size(); ++j) + { + const btSoftBody::Link& link = psb->m_links[j]; + btSoftBody::Node* node1 = link.m_n[0]; + btSoftBody::Node* node2 = link.m_n[1]; + btScalar r = link.m_rl; + + // elastic force + btVector3 dir = (node2->m_q - node1->m_q); + energy += 0.5 * m_elasticStiffness * (dir.norm() - r) * (dir.norm() - r); + } + } + return energy; + } + + virtual double totalDampingEnergy(btScalar dt) + { + double energy = 0; + int sz = 0; + for (int i = 0; i < m_softBodies.size(); ++i) + { + btSoftBody* psb = m_softBodies[i]; + if (!psb->isActive()) + { + continue; + } + for (int j = 0; j < psb->m_nodes.size(); ++j) + { + sz = btMax(sz, psb->m_nodes[j].index); + } + } + TVStack dampingForce; + dampingForce.resize(sz + 1); + for (int i = 0; i < dampingForce.size(); ++i) + dampingForce[i].setZero(); + addScaledDampingForce(0.5, dampingForce); + for (int i = 0; i < m_softBodies.size(); ++i) + { + btSoftBody* psb = m_softBodies[i]; + for (int j = 0; j < psb->m_nodes.size(); ++j) + { + const btSoftBody::Node& node = psb->m_nodes[j]; + energy -= dampingForce[node.index].dot(node.m_v) / dt; + } + } + return energy; + } + + virtual void addScaledElasticForceDifferential(btScalar scale, const TVStack& dx, TVStack& df) + { + // implicit damping force differential + for (int i = 0; i < m_softBodies.size(); ++i) + { + const btSoftBody* psb = m_softBodies[i]; + if (!psb->isActive()) + { + continue; + } + for (int j = 0; j < psb->m_links.size(); ++j) + { + const btSoftBody::Link& link = psb->m_links[j]; + btSoftBody::Node* node1 = link.m_n[0]; + btSoftBody::Node* node2 = link.m_n[1]; + size_t id1 = node1->index; + size_t id2 = node2->index; + btScalar r = link.m_rl; + + btVector3 dir = (node1->m_q - node2->m_q); + btScalar dir_norm = dir.norm(); + btVector3 dir_normalized = (dir_norm > SIMD_EPSILON) ? dir.normalized() : btVector3(0, 0, 0); + btVector3 dx_diff = dx[id1] - dx[id2]; + btVector3 scaled_df = btVector3(0, 0, 0); + btScalar scaled_k = scale * (link.m_bbending ? m_bendingStiffness : m_elasticStiffness); + if (dir_norm > SIMD_EPSILON) + { + scaled_df -= scaled_k * dir_normalized.dot(dx_diff) * dir_normalized; + scaled_df += scaled_k * dir_normalized.dot(dx_diff) * ((dir_norm - r) / dir_norm) * dir_normalized; + scaled_df -= scaled_k * ((dir_norm - r) / dir_norm) * dx_diff; + } + + df[id1] += scaled_df; + df[id2] -= scaled_df; + } + } + } + + virtual btDeformableLagrangianForceType getForceType() + { + return BT_MASSSPRING_FORCE; + } +}; + +#endif /* btMassSpring_h */ |