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use _gravity rather than _acceleration

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also tweaks and comments about supporting low gravity
This commit is contained in:
Andrew Meadows 2016-04-04 11:10:50 -07:00
parent 74058ac049
commit a53cb2e532
1 changed files with 53 additions and 21 deletions
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74
libraries/entities/src/EntityItem.cpp
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@ -895,9 +895,9 @@ void EntityItem::simulateKinematicMotion(float timeElapsed, bool setFlags) {
angularVelocity *= powf(1.0f - _angularDamping, timeElapsed); angularVelocity *= powf(1.0f - _angularDamping, timeElapsed);
} }
const float EPSILON_ANGULAR_VELOCITY_LENGTH_SQUARED = 0.0017453f * 0.0017453f; // 0.0017453 rad/sec = 0.1f degrees/sec const float MIN_KINEMATIC_ANGULAR_SPEED_SQUARED = 0.0017453f * 0.0017453f; // 0.0017453 rad/sec = 0.1f degrees/sec
if (glm::length2(angularVelocity) < EPSILON_ANGULAR_VELOCITY_LENGTH_SQUARED) { if (glm::length2(angularVelocity) < MIN_KINEMATIC_ANGULAR_SPEED_SQUARED) {
angularVelocity = ENTITY_ITEM_ZERO_VEC3; angularVelocity = Vectors::ZERO;
} else { } else {
// for improved agreement with the way Bullet integrates rotations we use an approximation // for improved agreement with the way Bullet integrates rotations we use an approximation
// and break the integration into bullet-sized substeps // and break the integration into bullet-sized substeps
@ -912,43 +912,75 @@ void EntityItem::simulateKinematicMotion(float timeElapsed, bool setFlags) {
isMoving = true; isMoving = true;
} }
} }
if (glm::length2(linearVelocity) > 0.0f) { glm::vec3 position = transform.getTranslation();
const float MIN_KINEMATIC_LINEAR_SPEED_SQUARED = 1.0e-6f; // 1mm/sec ^2
bool hasLinearVelocity = (glm::length2(linearVelocity) > MIN_KINEMATIC_LINEAR_SPEED_SQUARED );
if (hasLinearVelocity) {
// linear damping // linear damping
if (_damping > 0.0f) { if (_damping > 0.0f) {
linearVelocity *= powf(1.0f - _damping, timeElapsed); linearVelocity *= powf(1.0f - _damping, timeElapsed);
} }
glm::vec3 linearAcceleration = _acceleration; // integrate position forward sans acceleration
bool nonZeroAcceleration = (glm::length2(_acceleration) > 0.0f); position += linearVelocity * timeElapsed;
if (nonZeroAcceleration) { }
// acceleration is in world-frame but we need it in local-frame
bool success; const float MIN_KINEMATIC_GRAVITY_MOTION_SQUARED = 1.0e-6f; // 0.001 mm/sec^2
Transform parentTransform = getParentTransform(success); bool hasGravity = (glm::length2(_gravity) > MIN_KINEMATIC_GRAVITY_MOTION_SQUARED);
if (success) { if (hasGravity) {
linearAcceleration = glm::inverse(parentTransform.getRotation()) * linearAcceleration; // acceleration is in world-frame but we need it in local-frame
} glm::vec3 linearAcceleration = _gravity;
bool success;
Transform parentTransform = getParentTransform(success);
if (success) {
linearAcceleration = glm::inverse(parentTransform.getRotation()) * linearAcceleration;
} }
// integrate position forward // integrate position's acceleration term
glm::vec3 position = transform.getTranslation() + (linearVelocity * timeElapsed) + 0.5f * linearAcceleration * timeElapsed * timeElapsed; position += 0.5f * linearAcceleration * timeElapsed * timeElapsed;
transform.setTranslation(position);
// integrate linearVelocity // integrate linearVelocity
linearVelocity += linearAcceleration * timeElapsed; linearVelocity += linearAcceleration * timeElapsed;
}
const float EPSILON_LINEAR_VELOCITY_LENGTH_SQUARED = 1.0e-6f; // 1mm/sec ^2 if (hasLinearVelocity || hasGravity) {
if (glm::length2(linearVelocity) < EPSILON_LINEAR_VELOCITY_LENGTH_SQUARED) { // We MUST eventually stop kinematic motion for slow entities otherwise they will take
setVelocity(ENTITY_ITEM_ZERO_VEC3); // a looooong time to settle down, so we remeasure linear speed and zero the velocity
if (nonZeroAcceleration) { // if it is too small.
if (glm::length2(linearVelocity) < MIN_KINEMATIC_LINEAR_SPEED_SQUARED) {
linearVelocity = Vectors::ZERO;
if (!hasLinearVelocity) {
// Despite some gravity the final linear velocity is still too small to defeat the
// "effective resistance of free-space" which means we must reset position back to
// where it started since otherwise the entity may creep vveerrryy sslloowwllyy at
// a constant speed.
position = transform.getTranslation();
// Ultimately what this means is that there is some minimum gravity we can
// fully support for kinematic motion. It's exact value is a function of this
// entity's linearDamping and the hardcoded MIN_KINEMATIC_FOO parameters above,
// but the theoretical minimum gravity for zero damping at 90Hz is:
//
// minGravity = minSpeed / dt = 0.001 m/sec * 90 /sec = 0.09 m/sec^2
//
// In practice the true minimum is half that value, since if the frame rate is ever
// less than the expected then sometimes dt will be twice as long.
//
// Since we don't set isMoving true here this entity is destined to transition to
// STATIC unless it has some angular motion keeping it alive.
} else {
isMoving = true; isMoving = true;
} }
} else { } else {
isMoving = true; isMoving = true;
} }
} }
transform.setTranslation(position);
setLocalTransformAndVelocities(transform, linearVelocity, angularVelocity); setLocalTransformAndVelocities(transform, linearVelocity, angularVelocity);
if (!isMoving) { if (!isMoving) {
// flag this entity to be removed from kinematic motion // flag this entity to transition from KINEMATIC to STATIC
_dirtyFlags |= Simulation::DIRTY_MOTION_TYPE; _dirtyFlags |= Simulation::DIRTY_MOTION_TYPE;
} }
} }