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MotionState reports zero velocity for slow objects

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This reduces the number of updates for an Entity that is effectively
at rest due to a balance between some spring action and gravity, but
nevertheless has a slight non-zero velocity at the end of each
simulation step.
This commit is contained in:
Andrew Meadows 2015-07-09 11:29:53 -07:00
parent 542a5f100a
commit 46bca30698
2 changed files with 14 additions and 4 deletions
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6
libraries/physics/src/EntityMotionState.cpp
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@ -248,7 +248,7 @@ bool EntityMotionState::remoteSimulationOutOfSync(uint32_t simulationStep) {
btTransform xform = _body->getWorldTransform();
_serverPosition = bulletToGLM(xform.getOrigin());
_serverRotation = bulletToGLM(xform.getRotation());
_serverVelocity = bulletToGLM(_body->getLinearVelocity());
_serverVelocity = getBodyLinearVelocity();
_serverAngularVelocity = bulletToGLM(_body->getAngularVelocity());
_lastStep = simulationStep;
_serverActionData = _entity->getActionData();
@ -536,7 +536,7 @@ void EntityMotionState::bump(quint8 priority) {
void EntityMotionState::resetMeasuredBodyAcceleration() {
_lastMeasureStep = ObjectMotionState::getWorldSimulationStep();
if (_body) {
_lastVelocity = bulletToGLM(_body->getLinearVelocity());
_lastVelocity = getBodyLinearVelocity();
} else {
_lastVelocity = glm::vec3(0.0f);
}
@ -555,7 +555,7 @@ void EntityMotionState::measureBodyAcceleration() {
// Note: the integration equation for velocity uses damping: v1 = (v0 + a * dt) * (1 - D)^dt
// hence the equation for acceleration is: a = (v1 / (1 - D)^dt - v0) / dt
glm::vec3 velocity = bulletToGLM(_body->getLinearVelocity());
glm::vec3 velocity = getBodyLinearVelocity();
_measuredAcceleration = (velocity / powf(1.0f - _body->getLinearDamping(), dt) - _lastVelocity) * invDt;
_lastVelocity = velocity;
if (numSubsteps > PHYSICS_ENGINE_MAX_NUM_SUBSTEPS) {

12
libraries/physics/src/ObjectMotionState.cpp
View file

@ -80,7 +80,17 @@ void ObjectMotionState::setBodyGravity(const glm::vec3& gravity) const {
}
glm::vec3 ObjectMotionState::getBodyLinearVelocity() const {
return bulletToGLM(_body->getLinearVelocity());
// returns the body's velocity unless it is moving too slow in which case returns zero
btVector3 velocity = _body->getLinearVelocity();
// NOTE: the threshold to use here relates to the linear displacement threshold (dX) for sending updates
// to objects that are tracked server-side (e.g. entities which use dX = 2mm). Hence an object moving
// just under this velocity threshold would trigger an update about V/dX times per second.
const float MIN_LINEAR_SPEED_SQUARED = 0.0036f; // 6 mm/sec
if (velocity.length2() < MIN_LINEAR_SPEED_SQUARED) {
velocity *= 0.0f;
}
return bulletToGLM(velocity);
}
glm::vec3 ObjectMotionState::getObjectLinearVelocityChange() const {
return glm::vec3(0.0f); // Subclasses override where meaningful.