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reformulate friction

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This commit is contained in:
Xuchen Han
2019-07-18 09:16:01 -07:00
parent 7846dd38dd
commit 3430192db7
4 changed files with 36 additions and 31 deletions
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2
src/BulletSoftBody/btBackwardEulerObjective.cpp
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@@ -8,7 +8,7 @@
#include "btBackwardEulerObjective.h" #include "btBackwardEulerObjective.h"
btBackwardEulerObjective::btBackwardEulerObjective(btAlignedObjectArray<btSoftBody *>& softBodies, const TVStack& backup_v) btBackwardEulerObjective::btBackwardEulerObjective(btAlignedObjectArray<btSoftBody *>& softBodies, const TVStack& backup_v)
: cg(20) : cg(10)
, m_softBodies(softBodies) , m_softBodies(softBodies)
, projection(m_softBodies, m_dt) , projection(m_softBodies, m_dt)
, m_backupVelocity(backup_v) , m_backupVelocity(backup_v)

10
src/BulletSoftBody/btCGProjection.h
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@@ -43,22 +43,23 @@ struct Friction
btAlignedObjectArray<btScalar> m_impulse; btAlignedObjectArray<btScalar> m_impulse;
btAlignedObjectArray<btScalar> m_dv; btAlignedObjectArray<btScalar> m_dv;
btAlignedObjectArray<btVector3> m_direction; btAlignedObjectArray<btVector3> m_direction;
btAlignedObjectArray<btVector3> m_direction_prev;
btAlignedObjectArray<bool> m_static_prev; btAlignedObjectArray<bool> m_static_prev;
btAlignedObjectArray<btScalar> m_impulse_prev; btAlignedObjectArray<btScalar> m_impulse_prev;
btAlignedObjectArray<btScalar> m_dv_prev; btAlignedObjectArray<btScalar> m_dv_prev;
btAlignedObjectArray<btVector3> m_direction_prev;
btAlignedObjectArray<bool> m_released; btAlignedObjectArray<bool> m_released;
btAlignedObjectArray<btVector3> m_accumulated_impulse; btAlignedObjectArray<btScalar> m_accumulated_normal_impulse;
btAlignedObjectArray<btVector3> m_accumulated_tangent_impulse;
Friction() Friction()
{ {
m_static.push_back(false); m_static.push_back(false);
m_static_prev.push_back(false); m_static_prev.push_back(false);
m_direction.push_back(btVector3(0,0,0));
m_direction_prev.push_back(btVector3(0,0,0)); m_direction_prev.push_back(btVector3(0,0,0));
m_direction.push_back(btVector3(0,0,0));
m_impulse.push_back(0); m_impulse.push_back(0);
m_impulse_prev.push_back(0); m_impulse_prev.push_back(0);
@@ -66,7 +67,8 @@ struct Friction
m_dv.push_back(0); m_dv.push_back(0);
m_dv_prev.push_back(0); m_dv_prev.push_back(0);
m_accumulated_impulse.push_back(btVector3(0,0,0)); m_accumulated_normal_impulse.push_back(0);
m_accumulated_tangent_impulse.push_back(btVector3(0,0,0));
m_released.push_back(false); m_released.push_back(false);
} }
}; };

51
src/BulletSoftBody/btContactProjection.cpp
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@@ -11,7 +11,7 @@
void btContactProjection::update(const TVStack& dv, const TVStack& backupVelocity) void btContactProjection::update(const TVStack& dv, const TVStack& backupVelocity)
{ {
///solve rigid body constraints ///solve rigid body constraints
m_world->getSolverInfo().m_numIterations = 5; m_world->getSolverInfo().m_numIterations = 10;
m_world->btMultiBodyDynamicsWorld::solveConstraints(m_world->getSolverInfo()); m_world->btMultiBodyDynamicsWorld::solveConstraints(m_world->getSolverInfo());
// loop through constraints to set constrained values // loop through constraints to set constrained values
@@ -73,43 +73,44 @@ void btContactProjection::update(const TVStack& dv, const TVStack& backupVelocit
const btVector3 vr = vb - va; const btVector3 vr = vb - va;
const btScalar dn = btDot(vr, cti.m_normal); const btScalar dn = btDot(vr, cti.m_normal);
btVector3 impulse = c->m_c0 * vr; btVector3 impulse = c->m_c0 * vr;
const btVector3 impulse_normal = c->m_c0 *(cti.m_normal * dn); const btVector3 impulse_normal = c->m_c0 * (cti.m_normal * dn);
btVector3 impulse_tangent = impulse - impulse_normal; const btVector3 impulse_tangent = impulse - impulse_normal;
btScalar local_tangent_norm = impulse_tangent.norm();
btVector3 local_tangent_dir = btVector3(0,0,0);
if (local_tangent_norm > SIMD_EPSILON)
local_tangent_dir = impulse_tangent.normalized();
// accumulated impulse on the rb in this and all prev cg iterations // accumulated impulse on the rb in this and all prev cg iterations
friction.m_accumulated_impulse[j] += impulse; friction.m_accumulated_normal_impulse[j] += impulse_normal.dot(cti.m_normal);
btScalar accumulated_normal = friction.m_accumulated_impulse[j].dot(cti.m_normal); btScalar accumulated_normal = friction.m_accumulated_normal_impulse[j];
btVector3 accumulated_tangent = friction.m_accumulated_impulse[j] - accumulated_normal * cti.m_normal; btVector3 tangent = friction.m_accumulated_tangent_impulse[j] + impulse_tangent;
btScalar tangent_norm = tangent.norm();
// start friction handling // start friction handling
// copy old data // copy old data
friction.m_direction_prev[j] = friction.m_direction[j];
friction.m_impulse_prev[j] = friction.m_impulse[j]; friction.m_impulse_prev[j] = friction.m_impulse[j];
friction.m_dv_prev[j] = friction.m_dv[j]; friction.m_dv_prev[j] = friction.m_dv[j];
friction.m_static_prev[j] = friction.m_static[j]; friction.m_static_prev[j] = friction.m_static[j];
if (accumulated_normal < 0 && accumulated_tangent.norm() > SIMD_EPSILON) if (accumulated_normal < 0 && tangent_norm > SIMD_EPSILON)
{ {
friction.m_direction[j] = -local_tangent_dir;
btScalar compare1 = -accumulated_normal*c->m_c3; btScalar compare1 = -accumulated_normal*c->m_c3;
btScalar compare2 = accumulated_tangent.norm(); btScalar compare2 = tangent_norm;
// do not allow switching from static friction to dynamic friction // do not allow switching from static friction to dynamic friction
// it causes cg to explode // it causes cg to explode
if (-accumulated_normal*c->m_c3 < accumulated_tangent.norm() && friction.m_static_prev[j] == false && friction.m_released[j] == false) if (-accumulated_normal*c->m_c3 < tangent_norm && friction.m_static_prev[j] == false && friction.m_released[j] == false)
{ {
friction.m_static[j] = false; friction.m_static[j] = false;
friction.m_impulse[j] = -accumulated_normal*c->m_c3; friction.m_impulse[j] = -accumulated_normal*c->m_c3;
friction.m_dv[j] = -accumulated_normal*c->m_c3 *c->m_c2/m_dt ; friction.m_dv[j] = 0;
impulse = impulse_normal + (friction.m_impulse_prev[j] * friction.m_direction_prev[j])-(friction.m_impulse[j] * friction.m_direction[j]);
} }
else else
{ {
friction.m_static[j] = true; friction.m_static[j] = true;
friction.m_impulse[j] = accumulated_tangent.norm(); friction.m_impulse[j] = 0;
friction.m_dv[j] = accumulated_tangent.norm() * c->m_c2/m_dt; friction.m_dv[j] = local_tangent_norm * c->m_c2/m_dt;
impulse = impulse_normal + impulse_tangent;
} }
const btVector3 tangent_dir = accumulated_tangent.normalized();
friction.m_direction[j] = -tangent_dir;
} }
else else
{ {
@@ -117,9 +118,10 @@ void btContactProjection::update(const TVStack& dv, const TVStack& backupVelocit
friction.m_static[j] = false; friction.m_static[j] = false;
friction.m_impulse[j] = 0; friction.m_impulse[j] = 0;
friction.m_dv[j] = 0; friction.m_dv[j] = 0;
friction.m_direction[j] = btVector3(0,0,0);
impulse = impulse_normal;
} }
friction.m_accumulated_tangent_impulse[j] = -friction.m_impulse[j] * friction.m_direction[j];
friction.m_accumulated_impulse[j] = accumulated_normal * cti.m_normal - friction.m_impulse[j] * friction.m_direction[j];
if (1) // in the same CG solve, the set of constraits doesn't change if (1) // in the same CG solve, the set of constraits doesn't change
// if (dn <= SIMD_EPSILON) // if (dn <= SIMD_EPSILON)
{ {
@@ -134,7 +136,7 @@ void btContactProjection::update(const TVStack& dv, const TVStack& backupVelocit
// the incremental impulse: // the incremental impulse:
// in the normal direction it's the normal component of "impulse" // in the normal direction it's the normal component of "impulse"
// in the tangent direction it's the difference between the frictional impulse in the iteration and the previous iteration // in the tangent direction it's the difference between the frictional impulse in the iteration and the previous iteration
impulse = impulse_normal + (friction.m_impulse_prev[j] * friction.m_direction_prev[j]) - (friction.m_impulse[j] * friction.m_direction[j]); impulse = impulse_normal + (friction.m_impulse_prev[j] * friction.m_direction_prev[j])-(friction.m_impulse[j] * friction.m_direction[j]);
// impulse = impulse_normal; // impulse = impulse_normal;
if (cti.m_colObj->getInternalType() == btCollisionObject::CO_RIGID_BODY) if (cti.m_colObj->getInternalType() == btCollisionObject::CO_RIGID_BODY)
{ {
@@ -145,7 +147,7 @@ void btContactProjection::update(const TVStack& dv, const TVStack& backupVelocit
{ {
if (multibodyLinkCol) if (multibodyLinkCol)
{ {
double multiplier = 0.5; double multiplier = 1;
multibodyLinkCol->m_multiBody->applyDeltaVeeMultiDof(deltaV, -impulse.length() * multiplier); multibodyLinkCol->m_multiBody->applyDeltaVeeMultiDof(deltaV, -impulse.length() * multiplier);
} }
} }
@@ -273,7 +275,8 @@ void btContactProjection::setConstraintDirections()
frictions[j].m_dv_prev.push_back(0); frictions[j].m_dv_prev.push_back(0);
frictions[j].m_static.push_back(false); frictions[j].m_static.push_back(false);
frictions[j].m_static_prev.push_back(false); frictions[j].m_static_prev.push_back(false);
frictions[j].m_accumulated_impulse.push_back(btVector3(0,0,0)); frictions[j].m_accumulated_normal_impulse.push_back(0);
frictions[j].m_accumulated_tangent_impulse.push_back(btVector3(0,0,0));
frictions[j].m_released.push_back(false); frictions[j].m_released.push_back(false);
merged = true; merged = true;
break; break;

4
src/BulletSoftBody/btContactProjection.h
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@@ -124,7 +124,7 @@ public:
// clear the old constraint // clear the old constraint
if (friction.m_static_prev[j] == true) if (friction.m_static_prev[j] == true)
{ {
x[i] -= friction.m_direction_prev[j] * friction.m_dv_prev[j]; // x[i] -= friction.m_direction_prev[j] * friction.m_dv_prev[j];
} }
// add the new constraint // add the new constraint
if (friction.m_static[j] == true) if (friction.m_static[j] == true)
@@ -156,7 +156,7 @@ public:
// clear the old constraint // clear the old constraint
if (friction.m_static_prev[j] == true) if (friction.m_static_prev[j] == true)
{ {
x[i] -= friction.m_direction_prev[j] * friction.m_dv_prev[j]; // x[i] -= friction.m_direction_prev[j] * friction.m_dv_prev[j];
} }
// add the new constraint // add the new constraint
if (friction.m_static[j] == true) if (friction.m_static[j] == true)