Commit: 4db3b4da463538e1be2a36331653524d7f988188
Author: Sergej Reich
Date: Sat Apr 7 17:37:23 2018 +0200
Branches: master
https://developer.blender.org/rB4db3b4da463538e1be2a36331653524d7f988188
Bullet: Fix velocity calculation of new spring constraint
This is a backport of bullet commit: 86ca7dc
===================================================================
M
extern/bullet2/src/BulletDynamics/ConstraintSolver/btGeneric6DofSpring2Constraint.cpp
===================================================================
diff --git
a/extern/bullet2/src/BulletDynamics/ConstraintSolver/btGeneric6DofSpring2Constraint.cpp
b/extern/bullet2/src/BulletDynamics/ConstraintSolver/btGeneric6DofSpring2Constraint.cpp
index 49ff78c2621..31371944864 100644
---
a/extern/bullet2/src/BulletDynamics/ConstraintSolver/btGeneric6DofSpring2Constraint.cpp
+++
b/extern/bullet2/src/BulletDynamics/ConstraintSolver/btGeneric6DofSpring2Constraint.cpp
@@ -782,6 +782,12 @@ int btGeneric6DofSpring2Constraint::get_limit_motor_info2(
btScalar cfm = BT_ZERO;
btScalar mA = BT_ONE / m_rbA.getInvMass();
btScalar mB = BT_ONE / m_rbB.getInvMass();
+ if (rotational) {
+ btScalar rrA = (m_calculatedTransformA.getOrigin() -
transA.getOrigin()).length2();
+ btScalar rrB = (m_calculatedTransformB.getOrigin() -
transB.getOrigin()).length2();
+ if (m_rbA.getInvMass()) mA = mA * rrA + 1 /
(m_rbA.getInvInertiaTensorWorld() * ax1).length();
+ if (m_rbB.getInvMass()) mB = mB * rrB + 1 /
(m_rbB.getInvInertiaTensorWorld() * ax1).length();
+ }
btScalar m = mA > mB ? mB : mA;
btScalar angularfreq = sqrt(ks / m);
@@ -800,7 +806,18 @@ int btGeneric6DofSpring2Constraint::get_limit_motor_info2(
btScalar fd = -kd * (vel) * (rotational ? -1 : 1) * dt;
btScalar f = (fs+fd);
- info->m_constraintError[srow] = (vel + f * (rotational ? -1 :
1)) ;
+ // after the spring force affecting the body(es) the new velocity will
be
+ // vel + f / m * (rotational ? -1 : 1)
+ // so in theory this should be set here for m_constraintError
+ // (with m_constraintError we set a desired velocity for the affected
body(es))
+ // however in practice any value is fine as long as it is greater then
the "proper" velocity,
+ // because the m_lowerLimit and the m_upperLimit will determinate the
strength of the final pulling force
+ // so it is much simpler (and more robust) just to simply use inf (with
the proper sign)
+ // you may also wonder what if the current velocity (vel) so high that
the pulling force will not change its direction (in this iteration)
+ // will we not request a velocity with the wrong direction ?
+ // and the answare is not, because in practice during the solving the
current velocity is subtracted from the m_constraintError
+ // so the sign of the force that is really matters
+ info->m_constraintError[srow] = (rotational ? -1 : 1) * (f < 0 ?
-SIMD_INFINITY : SIMD_INFINITY);
btScalar minf = f < fd ? f : fd;
btScalar maxf = f < fd ? fd : f;
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