diff options
Diffstat (limited to 'extern/bullet2/src/BulletSoftBody/btDeformableCorotatedForce.h')
| -rw-r--r-- | extern/bullet2/src/BulletSoftBody/btDeformableCorotatedForce.h | 124 |
1 files changed, 124 insertions, 0 deletions
diff --git a/extern/bullet2/src/BulletSoftBody/btDeformableCorotatedForce.h b/extern/bullet2/src/BulletSoftBody/btDeformableCorotatedForce.h new file mode 100644 index 00000000000..dfd85523bc2 --- /dev/null +++ b/extern/bullet2/src/BulletSoftBody/btDeformableCorotatedForce.h @@ -0,0 +1,124 @@ +/* + 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_COROTATED_H +#define BT_COROTATED_H + +#include "btDeformableLagrangianForce.h" +#include "LinearMath/btPolarDecomposition.h" + +static inline int PolarDecomposition(const btMatrix3x3& m, btMatrix3x3& q, btMatrix3x3& s) +{ + static const btPolarDecomposition polar; + return polar.decompose(m, q, s); +} + +class btDeformableCorotatedForce : public btDeformableLagrangianForce +{ +public: + typedef btAlignedObjectArray<btVector3> TVStack; + btScalar m_mu, m_lambda; + btDeformableCorotatedForce() : m_mu(1), m_lambda(1) + { + } + + btDeformableCorotatedForce(btScalar mu, btScalar lambda) : m_mu(mu), m_lambda(lambda) + { + } + + virtual void addScaledForces(btScalar scale, TVStack& force) + { + addScaledElasticForce(scale, force); + } + + virtual void addScaledExplicitForce(btScalar scale, TVStack& force) + { + addScaledElasticForce(scale, force); + } + + virtual void addScaledDampingForce(btScalar scale, TVStack& force) + { + } + + virtual void addScaledElasticForce(btScalar scale, TVStack& force) + { + int numNodes = getNumNodes(); + btAssert(numNodes <= force.size()); + btVector3 grad_N_hat_1st_col = btVector3(-1, -1, -1); + for (int i = 0; i < m_softBodies.size(); ++i) + { + btSoftBody* psb = m_softBodies[i]; + for (int j = 0; j < psb->m_tetras.size(); ++j) + { + btSoftBody::Tetra& tetra = psb->m_tetras[j]; + btMatrix3x3 P; + firstPiola(tetra.m_F, P); + btVector3 force_on_node0 = P * (tetra.m_Dm_inverse.transpose() * grad_N_hat_1st_col); + btMatrix3x3 force_on_node123 = P * tetra.m_Dm_inverse.transpose(); + + btSoftBody::Node* node0 = tetra.m_n[0]; + btSoftBody::Node* node1 = tetra.m_n[1]; + btSoftBody::Node* node2 = tetra.m_n[2]; + btSoftBody::Node* node3 = tetra.m_n[3]; + size_t id0 = node0->index; + size_t id1 = node1->index; + size_t id2 = node2->index; + size_t id3 = node3->index; + + // elastic force + // explicit elastic force + btScalar scale1 = scale * tetra.m_element_measure; + force[id0] -= scale1 * force_on_node0; + force[id1] -= scale1 * force_on_node123.getColumn(0); + force[id2] -= scale1 * force_on_node123.getColumn(1); + force[id3] -= scale1 * force_on_node123.getColumn(2); + } + } + } + + void firstPiola(const btMatrix3x3& F, btMatrix3x3& P) + { + // btMatrix3x3 JFinvT = F.adjoint(); + btScalar J = F.determinant(); + P = F.adjoint().transpose() * (m_lambda * (J - 1)); + if (m_mu > SIMD_EPSILON) + { + btMatrix3x3 R, S; + if (J < 1024 * SIMD_EPSILON) + R.setIdentity(); + else + PolarDecomposition(F, R, S); // this QR is not robust, consider using implicit shift svd + /*https://fuchuyuan.github.io/research/svd/paper.pdf*/ + P += (F - R) * 2 * m_mu; + } + } + + virtual void addScaledElasticForceDifferential(btScalar scale, const TVStack& dx, TVStack& df) + { + } + + virtual void addScaledDampingForceDifferential(btScalar scale, const TVStack& dv, TVStack& df) + { + } + + virtual void buildDampingForceDifferentialDiagonal(btScalar scale, TVStack& diagA) {} + + virtual btDeformableLagrangianForceType getForceType() + { + return BT_COROTATED_FORCE; + } +}; + +#endif /* btCorotated_h */ |