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_MOUSE_PICKING_FORCE_H 17 #define BT_MOUSE_PICKING_FORCE_H 18 19 #include "btDeformableLagrangianForce.h" 20 21 class btDeformableMousePickingForce : 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 btScalar m_elasticStiffness, m_dampingStiffness; 26 const btSoftBody::Face& m_face; 27 btVector3 m_mouse_pos; 28 btScalar m_maxForce; 29 30 public: 31 typedef btAlignedObjectArray<btVector3> TVStack; m_elasticStiffness(k)32 btDeformableMousePickingForce(btScalar k, btScalar d, const btSoftBody::Face& face, const btVector3& mouse_pos, btScalar maxForce = 0.3) : m_elasticStiffness(k), m_dampingStiffness(d), m_face(face), m_mouse_pos(mouse_pos), m_maxForce(maxForce) 33 { 34 } 35 addScaledForces(btScalar scale,TVStack & force)36 virtual void addScaledForces(btScalar scale, TVStack& force) 37 { 38 addScaledDampingForce(scale, force); 39 addScaledElasticForce(scale, force); 40 } 41 addScaledExplicitForce(btScalar scale,TVStack & force)42 virtual void addScaledExplicitForce(btScalar scale, TVStack& force) 43 { 44 addScaledElasticForce(scale, force); 45 } 46 addScaledDampingForce(btScalar scale,TVStack & force)47 virtual void addScaledDampingForce(btScalar scale, TVStack& force) 48 { 49 for (int i = 0; i < 3; ++i) 50 { 51 btVector3 v_diff = m_face.m_n[i]->m_v; 52 btVector3 scaled_force = scale * m_dampingStiffness * v_diff; 53 if ((m_face.m_n[i]->m_x - m_mouse_pos).norm() > SIMD_EPSILON) 54 { 55 btVector3 dir = (m_face.m_n[i]->m_x - m_mouse_pos).normalized(); 56 scaled_force = scale * m_dampingStiffness * v_diff.dot(dir) * dir; 57 } 58 force[m_face.m_n[i]->index] -= scaled_force; 59 } 60 } 61 addScaledElasticForce(btScalar scale,TVStack & force)62 virtual void addScaledElasticForce(btScalar scale, TVStack& force) 63 { 64 btScalar scaled_stiffness = scale * m_elasticStiffness; 65 for (int i = 0; i < 3; ++i) 66 { 67 btVector3 dir = (m_face.m_n[i]->m_q - m_mouse_pos); 68 btVector3 scaled_force = scaled_stiffness * dir; 69 if (scaled_force.safeNorm() > m_maxForce) 70 { 71 scaled_force.safeNormalize(); 72 scaled_force *= m_maxForce; 73 } 74 force[m_face.m_n[i]->index] -= scaled_force; 75 } 76 } 77 addScaledDampingForceDifferential(btScalar scale,const TVStack & dv,TVStack & df)78 virtual void addScaledDampingForceDifferential(btScalar scale, const TVStack& dv, TVStack& df) 79 { 80 btScalar scaled_k_damp = m_dampingStiffness * scale; 81 for (int i = 0; i < 3; ++i) 82 { 83 btVector3 local_scaled_df = scaled_k_damp * dv[m_face.m_n[i]->index]; 84 if ((m_face.m_n[i]->m_x - m_mouse_pos).norm() > SIMD_EPSILON) 85 { 86 btVector3 dir = (m_face.m_n[i]->m_x - m_mouse_pos).normalized(); 87 local_scaled_df = scaled_k_damp * dv[m_face.m_n[i]->index].dot(dir) * dir; 88 } 89 df[m_face.m_n[i]->index] -= local_scaled_df; 90 } 91 } 92 buildDampingForceDifferentialDiagonal(btScalar scale,TVStack & diagA)93 virtual void buildDampingForceDifferentialDiagonal(btScalar scale, TVStack& diagA) {} 94 totalElasticEnergy(btScalar dt)95 virtual double totalElasticEnergy(btScalar dt) 96 { 97 double energy = 0; 98 for (int i = 0; i < 3; ++i) 99 { 100 btVector3 dir = (m_face.m_n[i]->m_q - m_mouse_pos); 101 btVector3 scaled_force = m_elasticStiffness * dir; 102 if (scaled_force.safeNorm() > m_maxForce) 103 { 104 scaled_force.safeNormalize(); 105 scaled_force *= m_maxForce; 106 } 107 energy += 0.5 * scaled_force.dot(dir); 108 } 109 return energy; 110 } 111 totalDampingEnergy(btScalar dt)112 virtual double totalDampingEnergy(btScalar dt) 113 { 114 double energy = 0; 115 for (int i = 0; i < 3; ++i) 116 { 117 btVector3 v_diff = m_face.m_n[i]->m_v; 118 btVector3 scaled_force = m_dampingStiffness * v_diff; 119 if ((m_face.m_n[i]->m_x - m_mouse_pos).norm() > SIMD_EPSILON) 120 { 121 btVector3 dir = (m_face.m_n[i]->m_x - m_mouse_pos).normalized(); 122 scaled_force = m_dampingStiffness * v_diff.dot(dir) * dir; 123 } 124 energy -= scaled_force.dot(m_face.m_n[i]->m_v) / dt; 125 } 126 return energy; 127 } 128 addScaledElasticForceDifferential(btScalar scale,const TVStack & dx,TVStack & df)129 virtual void addScaledElasticForceDifferential(btScalar scale, const TVStack& dx, TVStack& df) 130 { 131 btScalar scaled_stiffness = scale * m_elasticStiffness; 132 for (int i = 0; i < 3; ++i) 133 { 134 btVector3 dir = (m_face.m_n[i]->m_q - m_mouse_pos); 135 btScalar dir_norm = dir.norm(); 136 btVector3 dir_normalized = (dir_norm > SIMD_EPSILON) ? dir.normalized() : btVector3(0, 0, 0); 137 int id = m_face.m_n[i]->index; 138 btVector3 dx_diff = dx[id]; 139 btScalar r = 0; // rest length is 0 for picking spring 140 btVector3 scaled_df = btVector3(0, 0, 0); 141 if (dir_norm > SIMD_EPSILON) 142 { 143 scaled_df -= scaled_stiffness * dir_normalized.dot(dx_diff) * dir_normalized; 144 scaled_df += scaled_stiffness * dir_normalized.dot(dx_diff) * ((dir_norm - r) / dir_norm) * dir_normalized; 145 scaled_df -= scaled_stiffness * ((dir_norm - r) / dir_norm) * dx_diff; 146 } 147 df[id] += scaled_df; 148 } 149 } 150 setMousePos(const btVector3 & p)151 void setMousePos(const btVector3& p) 152 { 153 m_mouse_pos = p; 154 } 155 getForceType()156 virtual btDeformableLagrangianForceType getForceType() 157 { 158 return BT_MOUSE_PICKING_FORCE; 159 } 160 }; 161 162 #endif /* btMassSpring_h */ 163