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Change the function used for the linear and angular damping of the rigid bodies

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This commit is contained in:
Daniel Chappuis 2021-09-09 00:05:45 +02:00
parent ce0bb3b9a6
commit 1273f3a83c
3 changed files with 18 additions and 17 deletions
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1
CHANGELOG.md
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@ -134,6 +134,7 @@ do not hesitate to take a look at the user manual.
- The RigidBody::recomputeMassInformation() method has been renamed to RigidBody::updateMassPropertiesFromColliders.
- Now, you need to manually call the RigidBody::updateMassPropertiesFromColliders() method after adding colliders to a rigid body to recompute its inertia tensor, center of mass and mass. There are other methods that you can use form that (see the user manual)
- The RigidBody::applyForce() method has been renamed to RigidBody::applyForceAtWorldPosition()
- The linear and angular damping function of the rigid bodies has been changed
- The rendering in the testbed application has been improved
- Many of the data inside the library have been refactored for better caching and easier parallelization in the future
- The old Logger class has been renamed to DefaultLogger

14
src/body/RigidBody.cpp
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@ -302,7 +302,7 @@ void RigidBody::applyWorldForceAtCenterOfMass(const Vector3& force) {
// Return the linear velocity damping factor
/**
* @return The linear damping factor of this body
* @return The linear damping factor of this body (in range [0; +inf]). Zero means no damping.
*/
decimal RigidBody::getLinearDamping() const {
return mWorld.mRigidBodyComponents.getLinearDamping(mEntity);
@ -310,7 +310,7 @@ decimal RigidBody::getLinearDamping() const {
// Return the angular velocity damping factor
/**
* @return The angular damping factor of this body
* @return The angular damping factor of this body (in range [0; +inf]). Zero means no damping.
*/
decimal RigidBody::getAngularDamping() const {
return mWorld.mRigidBodyComponents.getAngularDamping(mEntity);
@ -730,10 +730,9 @@ void RigidBody::enableGravity(bool isEnabled) {
(isEnabled ? "true" : "false"), __FILE__, __LINE__);
}
// Set the linear damping factor. This is the ratio of the linear velocity
// that the body will lose every at seconds of simulation.
// Set the linear damping factor.
/**
* @param linearDamping The linear damping factor of this body
* @param linearDamping The linear damping factor of this body (in range [0; +inf]). Zero means no damping.
*/
void RigidBody::setLinearDamping(decimal linearDamping) {
assert(linearDamping >= decimal(0.0));
@ -752,10 +751,9 @@ void RigidBody::setLinearDamping(decimal linearDamping) {
}
}
// Set the angular damping factor. This is the ratio of the angular velocity
// that the body will lose at every seconds of simulation.
// Set the angular damping factor.
/**
* @param angularDamping The angular damping factor of this body
* @param angularDamping The angular damping factor of this body (in range [0; +inf]). Zero means no damping.
*/
void RigidBody::setAngularDamping(decimal angularDamping) {
assert(angularDamping >= decimal(0.0));

20
src/systems/DynamicsSystem.cpp
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@ -157,24 +157,26 @@ void DynamicsSystem::integrateRigidBodiesVelocities(decimal timeStep) {
// Apply the velocity damping
// Damping force : F_c = -c' * v (c=damping factor)
// Equation : m * dv/dt = -c' * v
// => dv/dt = -c * v (with c=c'/m)
// => dv/dt + c * v = 0
// Differential Equation : m * dv/dt = -c' * v
// => dv/dt = -c * v (with c=c'/m)
// => dv/dt + c * v = 0
// Solution : v(t) = v0 * e^(-c * t)
// => v(t + dt) = v0 * e^(-c(t + dt))
// = v0 * e^(-ct) * e^(-c * dt)
// = v0 * e^(-c * t) * e^(-c * dt)
// = v(t) * e^(-c * dt)
// => v2 = v1 * e^(-c * dt)
// Using Taylor Serie for e^(-x) : e^x ~ 1 + x + x^2/2! + ...
// => e^(-x) ~ 1 - x
// => v2 = v1 * (1 - c * dt)
// Using Padé's approximation of the exponential function:
// Reference: https://mathworld.wolfram.com/PadeApproximant.html
// e^x ~ 1 / (1 - x)
// => e^(-c * dt) ~ 1 / (1 + c * dt)
// => v2 = v1 * 1 / (1 + c * dt)
const uint32 nbRigidBodyComponents = mRigidBodyComponents.getNbEnabledComponents();
for (uint32 i=0; i < nbRigidBodyComponents; i++) {
const decimal linDampingFactor = mRigidBodyComponents.mLinearDampings[i];
const decimal angDampingFactor = mRigidBodyComponents.mAngularDampings[i];
const decimal linearDamping = std::pow(decimal(1.0) - linDampingFactor, timeStep);
const decimal angularDamping = std::pow(decimal(1.0) - angDampingFactor, timeStep);
const decimal linearDamping = decimal(1.0) / (decimal(1.0) + linDampingFactor * timeStep);
const decimal angularDamping = decimal(1.0) / (decimal(1.0) + angDampingFactor * timeStep);
mRigidBodyComponents.mConstrainedLinearVelocities[i] = mRigidBodyComponents.mConstrainedLinearVelocities[i] * linearDamping;
mRigidBodyComponents.mConstrainedAngularVelocities[i] = mRigidBodyComponents.mConstrainedAngularVelocities[i] * angularDamping;
}