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//! Manages and solves contacts, joints, and other constraints.
//!
//! See [`SolverPlugin`].
pub mod contact;
pub mod joints;
pub mod softness_parameters;
pub mod xpbd;
use crate::prelude::*;
use bevy::prelude::*;
use self::{
contact::ContactConstraint,
dynamics::integrator::IntegrationSet,
softness_parameters::{SoftnessCoefficients, SoftnessParameters},
};
/// Manages and solves contacts, joints, and other constraints.
///
/// Note that the [`ContactConstraints`] are currently generated by tbe [`NarrowPhasePlugin`].
///
/// ## Implementation
///
/// The solver primarily uses TGS Soft, an impulse-based solver with substepping and [soft constraints](softness_parameters).
/// Warm starting is used to improve convergence, along with a relaxation pass to reduce overshooting.
///
/// [Speculative collision](dynamics::ccd#speculative-collision) is used by default to prevent tunneling.
/// Optional [sweep-based Continuous Collision Detection (CCD)](dynamics::ccd#swept-ccd) is handled by the [`CcdPlugin`].
///
/// [Joints](joints) and user constraints are currently solved using [Extended Position-Based Dynamics (XPBD)](xpbd).
/// In the future, they may transition to an impulse-based approach as well.
///
/// ## Steps
///
/// Below are the main steps of the `SolverPlugin`.
///
/// 1. [Generate and prepare constraints](collision::narrow_phase::NarrowPhaseSet::GenerateConstraints)
/// 2. Substepping loop (runs the [`SubstepSchedule`] [`SubstepCount`] times)
/// 1. [Integrate velocities](IntegrationSet::Velocity)
/// 2. [Warm start](SubstepSolverSet::WarmStart)
/// 3. [Solve constraints with bias](SubstepSolverSet::SolveConstraints)
/// 4. [Integrate positions](IntegrationSet::Position)
/// 5. [Solve constraints without bias to relax velocities](SubstepSolverSet::Relax)
/// 6. [Solve XPBD constraints (joints)](SubstepSolverSet::SolveXpbdConstraints)
/// 7. [Solve user-defined constraints](SubstepSolverSet::SolveUserConstraints)
/// 8. [Update velocities after XPBD constraint solving.](SubstepSolverSet::XpbdVelocityProjection)
/// 3. [Apply restitution](SolverSet::Restitution)
/// 4. [Finalize positions by applying](SolverSet::ApplyTranslation) [`AccumulatedTranslation`]
/// 5. [Store contact impulses for next frame's warm starting](SolverSet::StoreContactImpulses)
pub struct SolverPlugin {
length_unit: Scalar,
}
impl Default for SolverPlugin {
fn default() -> Self {
Self::new_with_length_unit(1.0)
}
}
impl SolverPlugin {
/// Creates a [`SolverPlugin`] with the given approximate dimensions of most objects.
///
/// The length unit will be used for initializing the [`PhysicsLengthUnit`]
/// resource unless it already exists.
pub fn new_with_length_unit(unit: Scalar) -> Self {
Self { length_unit: unit }
}
}
impl Plugin for SolverPlugin {
fn build(&self, app: &mut App) {
app.init_resource::<SolverConfig>()
.init_resource::<ContactSoftnessCoefficients>()
.init_resource::<ContactConstraints>();
if !app.world().contains_resource::<PhysicsLengthUnit>() {
app.insert_resource(PhysicsLengthUnit(self.length_unit));
}
// Get the `PhysicsSchedule`, and panic if it doesn't exist.
let physics = app
.get_schedule_mut(PhysicsSchedule)
.expect("add PhysicsSchedule first");
physics.add_systems(update_contact_softness.before(PhysicsStepSet::NarrowPhase));
// See `SolverSet` for what each system set is responsible for.
physics.configure_sets(
(
SolverSet::PreSubstep,
SolverSet::Substep,
SolverSet::PostSubstep,
SolverSet::Restitution,
SolverSet::ApplyTranslation,
SolverSet::StoreContactImpulses,
)
.chain()
.in_set(PhysicsStepSet::Solver),
);
// Update previous rotations before the substepping loop.
physics.add_systems(
(|mut query: Query<(&Rotation, &mut PreviousRotation)>| {
for (rot, mut prev_rot) in &mut query {
prev_rot.0 = *rot;
}
})
.in_set(SolverSet::PreSubstep),
);
// Finalize the positions of bodies by applying the `AccumulatedTranslation`.
// This runs after the substepping loop.
physics.add_systems(
apply_translation
.chain()
.in_set(SolverSet::ApplyTranslation),
);
// Apply restitution.
physics.add_systems(solve_restitution.in_set(SolverSet::Restitution));
// Store the current contact impulses for the next frame's warm starting.
physics.add_systems(store_contact_impulses.in_set(SolverSet::StoreContactImpulses));
// Get the `SubstepSchedule`, and panic if it doesn't exist.
let substeps = app
.get_schedule_mut(SubstepSchedule)
.expect("add SubstepSchedule first");
// See `SolverSet` for what each system set is responsible for.
substeps.configure_sets(
(
IntegrationSet::Velocity,
SubstepSolverSet::WarmStart,
SubstepSolverSet::SolveConstraints,
IntegrationSet::Position,
SubstepSolverSet::Relax,
SubstepSolverSet::SolveXpbdConstraints,
SubstepSolverSet::SolveUserConstraints,
SubstepSolverSet::XpbdVelocityProjection,
)
.chain(),
);
// Warm start the impulses.
// This applies the impulses stored from the previous substep,
// which improves convergence.
substeps.add_systems(warm_start.in_set(SubstepSolverSet::WarmStart));
// Solve velocities using a position bias.
substeps.add_systems(
(
|mut bodies: Query<RigidBodyQuery>,
mut constraints: ResMut<ContactConstraints>,
solver_config: Res<SolverConfig>,
length_unit: Res<PhysicsLengthUnit>,
time: Res<Time>| {
solve_contacts(
&mut bodies,
&mut constraints.0,
time.delta_seconds_adjusted(),
1,
true,
solver_config.max_overlap_solve_speed * length_unit.0,
);
},
)
.in_set(SubstepSolverSet::SolveConstraints),
);
// Relax biased velocities and impulses.
// This reduces overshooting caused by warm starting.
substeps.add_systems(
(
|mut bodies: Query<RigidBodyQuery>,
mut constraints: ResMut<ContactConstraints>,
solver_config: Res<SolverConfig>,
length_unit: Res<PhysicsLengthUnit>,
time: Res<Time>| {
solve_contacts(
&mut bodies,
&mut constraints.0,
time.delta_seconds_adjusted(),
1,
false,
solver_config.max_overlap_solve_speed * length_unit.0,
);
},
)
.in_set(SubstepSolverSet::Relax),
);
// Solve joints with XPBD.
substeps.add_systems(
(
|mut query: Query<(
&AccumulatedTranslation,
&mut PreSolveAccumulatedTranslation,
&Rotation,
&mut PreSolveRotation,
)>| {
for (translation, mut pre_solve_translation, rotation, mut previous_rotation) in
&mut query
{
pre_solve_translation.0 = translation.0;
previous_rotation.0 = *rotation;
}
},
xpbd::solve_constraint::<FixedJoint, 2>,
xpbd::solve_constraint::<RevoluteJoint, 2>,
#[cfg(feature = "3d")]
xpbd::solve_constraint::<SphericalJoint, 2>,
xpbd::solve_constraint::<PrismaticJoint, 2>,
xpbd::solve_constraint::<DistanceJoint, 2>,
)
.chain()
.in_set(SubstepSolverSet::SolveXpbdConstraints),
);
// Perform XPBD velocity updates after constraint solving.
substeps.add_systems(
(
xpbd::project_linear_velocity,
xpbd::project_angular_velocity,
joint_damping::<FixedJoint>,
joint_damping::<RevoluteJoint>,
#[cfg(feature = "3d")]
joint_damping::<SphericalJoint>,
joint_damping::<PrismaticJoint>,
joint_damping::<DistanceJoint>,
)
.chain()
.in_set(SubstepSolverSet::XpbdVelocityProjection),
);
}
}
// TODO: Where should this type be and which plugin should initialize it?
/// A units-per-meter scaling factor that adjusts the engine's internal properties
/// to the scale of the world.
///
/// For example, a 2D game might use pixels as units and have an average object size
/// of around 100 pixels. By setting the length unit to `100.0`, the physics engine
/// will interpret 100 pixels as 1 meter for internal thresholds, improving stability.
///
/// Note that this is *not* used to scale forces or any other user-facing inputs or outputs.
/// Instead, the value is only used to scale some internal length-based tolerances, such as
/// [`SleepingThreshold::linear`] and [`NarrowPhaseConfig::default_speculative_margin`],
/// as well as the scale used for [debug rendering](PhysicsDebugPlugin).
///
/// Choosing the appropriate length unit can help improve stability and robustness.
///
/// Default: `1.0`
///
/// # Example
///
/// The [`PhysicsLengthUnit`] can be inserted as a resource like normal,
/// but it can also be specified through the [`PhysicsPlugins`] plugin group.
///
/// ```no_run
/// # #[cfg(feature = "2d")]
/// use avian2d::prelude::*;
/// use bevy::prelude::*;
///
/// # #[cfg(feature = "2d")]
/// fn main() {
/// App::new()
/// .add_plugins((
/// DefaultPlugins,
/// // A 2D game with 100 pixels per meter
/// PhysicsPlugins::default().with_length_unit(100.0),
/// ))
/// .run();
/// }
/// # #[cfg(not(feature = "2d"))]
/// # fn main() {} // Doc test needs main
/// ```
#[derive(Resource, Clone, Debug, Deref, DerefMut, PartialEq, Reflect)]
#[reflect(Resource)]
pub struct PhysicsLengthUnit(pub Scalar);
impl Default for PhysicsLengthUnit {
fn default() -> Self {
Self(1.0)
}
}
/// System sets for the constraint solver.
///
/// ## Steps
///
/// Below is the core solver loop.
///
/// 1. Generate and prepare constraints ([`NarrowPhaseSet::GenerateConstraints`](collision::narrow_phase::NarrowPhaseSet::GenerateConstraints))
/// 2. Substepping loop (runs the [`SubstepSchedule`] [`SubstepCount`] times; see [`SolverSet::Substep`])
/// 3. Apply restitution ([`SolverSet::Restitution`])
/// 4. Finalize positions by applying [`AccumulatedTranslation`] ([`SolverSet::ApplyTranslation`])
/// 5. Store contact impulses for next frame's warm starting ([`SolverSet::StoreContactImpulses`])
#[derive(SystemSet, Clone, Copy, Debug, PartialEq, Eq, Hash)]
pub enum SolverSet {
/// A system set for systems running just before the substepping loop.
PreSubstep,
/// A system set for the substepping loop.
Substep,
/// A system set for systems running just after the substepping loop.
PostSubstep,
/// Applies [restitution](Restitution) for bodies after solving overlap.
Restitution,
/// Finalizes the positions of bodies by applying the [`AccumulatedTranslation`].
///
/// Constraints don't modify the positions of bodies directly and instead adds
/// to this translation to improve numerical stability when bodies are far from the world origin.
ApplyTranslation,
/// Copies contact impulses from [`ContactConstraints`] to the contacts in [`Collisions`].
/// They will be used for [warm starting](SubstepSolverSet::WarmStart) the next frame or substep.
StoreContactImpulses,
}
/// System sets for the substepped part of the constraint solver.
///
/// ## Steps
///
/// 1. Integrate velocity ([`IntegrationSet::Velocity`])
/// 2. Warm start ([`SubstepSolverSet::WarmStart`])
/// 3. Solve constraints with bias ([`SubstepSolverSet::SolveConstraints`])
/// 4. Integrate positions ([`IntegrationSet::Position`])
/// 5. Solve constraints without bias to relax velocities ([`SubstepSolverSet::Relax`])
/// 6. Solve joints using Extended Position-Based Dynamics (XPBD). ([`SubstepSolverSet::SolveXpbdConstraints`])
/// 7. Solve user-defined constraints. ([`SubstepSolverSet::SolveUserConstraints`])
/// 8. Update velocities after XPBD constraint solving. ([`SubstepSolverSet::XpbdVelocityProjection`])
#[derive(SystemSet, Clone, Copy, Debug, PartialEq, Eq, Hash)]
pub enum SubstepSolverSet {
/// Warm starts the solver by applying the impulses from the previous frame or substep.
///
/// This significantly improves convergence, but by itself can lead to overshooting.
/// Overshooting is reduced by [relaxing](SubstepSolverSet::Relax) the biased velocities
/// by running the solver a second time *without* bias.
WarmStart,
/// Solves velocity constraints using a position bias that boosts the response
/// to account for the constraint error.
SolveConstraints,
/// Solves velocity constraints without a position bias to relax the biased velocities
/// and impulses. This reduces overshooting caused by [warm starting](SubstepSolverSet::WarmStart).
Relax,
/// Solves joints using Extended Position-Based Dynamics (XPBD).
SolveXpbdConstraints,
/// A system set for user constraints.
SolveUserConstraints,
/// Performs velocity updates after XPBD constraint solving.
XpbdVelocityProjection,
}
/// Configuration parameters for the constraint solver that handles
/// things like contacts and joints.
///
/// These are tuned to give good results for most applications, but can
/// be configured if more control over the simulation behavior is needed.
#[derive(Resource, Clone, Debug, PartialEq, Reflect)]
#[reflect(Resource)]
pub struct SolverConfig {
/// The damping ratio used for contact stabilization.
///
/// Lower values make contacts more compliant or "springy",
/// allowing more visible penetration before overlap has been
/// resolved and the contact has been stabilized.
///
/// Consider using a higher damping ratio if contacts seem too soft.
/// Note that making the value too large can cause instability.
///
/// Default: `10.0`.
pub contact_damping_ratio: Scalar,
/// Scales the frequency used for contacts. A higher frequency
/// makes contact responses faster and reduces visible springiness,
/// but can hurt stability.
///
/// The solver computes the frequency using the time step and substep count,
/// and limits the maximum frequency to be at most half of the time step due to
/// [Nyquist's theorem](https://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem).
/// This factor scales the resulting frequency, which can lead to unstable behavior
/// if the factor is too large.
///
/// Default: `1.5`
pub contact_frequency_factor: Scalar,
/// The maximum speed at which overlapping bodies are pushed apart by the solver.
///
/// With a small value, overlap is resolved gently and gradually, while large values
/// can result in more snappy behavior.
///
/// This is implicitly scaled by the [`PhysicsLengthUnit`].
///
/// Default: `4.0`
pub max_overlap_solve_speed: Scalar,
/// The coefficient in the `[0, 1]` range applied to
/// [warm start](SubstepSolverSet::WarmStart) impulses.
///
/// Warm starting uses the impulses from the previous frame as the initial
/// solution for the current frame. This helps the solver reach the desired
/// state much faster, meaning that *convergence* is improved.
///
/// The coefficient should typically be set to `1.0`.
///
/// Default: `1.0`
pub warm_start_coefficient: Scalar,
/// The minimum speed along the contact normal in units per second
/// for [restitution](Restitution) to be applied.
///
/// An appropriate threshold should typically be small enough that objects
/// keep bouncing until the bounces are effectively unnoticeable,
/// but large enough that restitution is not applied unnecessarily,
/// improving performance and stability.
///
/// This is implicitly scaled by the [`PhysicsLengthUnit`].
///
/// Default: `1.0`
pub restitution_threshold: Scalar,
/// The number of iterations used for applying [restitution](Restitution).
///
/// A higher number of iterations can result in more accurate bounces,
/// but it only makes a difference when there are more than one contact point.
///
/// For example, with just one iteration, a cube falling flat on the ground
/// might bounce and rotate to one side, because the impulses are applied
/// to the corners sequentially, and some of the impulses are likely to be larger
/// than the others. With multiple iterations, the impulses are applied more evenly.
///
/// Default: `1`
pub restitution_iterations: usize,
}
impl Default for SolverConfig {
fn default() -> Self {
Self {
contact_damping_ratio: 10.0,
contact_frequency_factor: 1.5,
max_overlap_solve_speed: 4.0,
warm_start_coefficient: 1.0,
restitution_threshold: 1.0,
restitution_iterations: 1,
}
}
}
/// The [`SoftnessCoefficients`] used for contacts.
///
/// **Note**: This resource is updated automatically and not intended to be modified manually.
/// Use the [`SolverConfig`] resource instead for tuning contact behavior.
#[derive(Resource, Clone, Copy, PartialEq, Reflect)]
#[reflect(Resource)]
pub struct ContactSoftnessCoefficients {
/// The [`SoftnessCoefficients`] used for contacts against dynamic bodies.
pub dynamic: SoftnessCoefficients,
/// The [`SoftnessCoefficients`] used for contacts against static or kinematic bodies.
pub non_dynamic: SoftnessCoefficients,
}
impl Default for ContactSoftnessCoefficients {
fn default() -> Self {
Self {
dynamic: SoftnessParameters::new(10.0, 30.0).compute_coefficients(1.0 / 60.0),
non_dynamic: SoftnessParameters::new(10.0, 60.0).compute_coefficients(1.0 / 60.0),
}
}
}
fn update_contact_softness(
mut coefficients: ResMut<ContactSoftnessCoefficients>,
solver_config: Res<SolverConfig>,
physics_time: Res<Time<Physics>>,
substep_time: Res<Time<Substeps>>,
) {
if solver_config.is_changed() || physics_time.is_changed() || substep_time.is_changed() {
let dt = physics_time.delta_seconds_f64() as Scalar;
let h = substep_time.delta_seconds_f64() as Scalar;
// The contact frequency should at most be half of the time step due to Nyquist's theorem.
// https://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem
let max_hz = 1.0 / (dt * 2.0);
let hz = solver_config.contact_frequency_factor * max_hz.min(0.25 / h);
coefficients.dynamic = SoftnessParameters::new(solver_config.contact_damping_ratio, hz)
.compute_coefficients(h);
// TODO: Perhaps the non-dynamic softness should be configurable separately.
// Make contacts against static and kinematic bodies stiffer to avoid clipping through the environment.
coefficients.non_dynamic =
SoftnessParameters::new(solver_config.contact_damping_ratio, 2.0 * hz)
.compute_coefficients(h);
}
}
/// A resource that stores >the contact constraints.
#[derive(Resource, Default, Deref, DerefMut)]
pub struct ContactConstraints(pub Vec<ContactConstraint>);
/// Warm starts the solver by applying the impulses from the previous frame or substep.
///
/// See [`SubstepSolverSet::WarmStart`] for more information.
fn warm_start(
mut bodies: Query<RigidBodyQuery>,
mut constraints: ResMut<ContactConstraints>,
solver_config: Res<SolverConfig>,
) {
for constraint in constraints.iter_mut() {
debug_assert!(!constraint.points.is_empty());
let Ok([mut body1, mut body2]) =
bodies.get_many_mut([constraint.entity1, constraint.entity2])
else {
continue;
};
let normal = constraint.normal;
let tangent_directions =
constraint.tangent_directions(body1.linear_velocity.0, body2.linear_velocity.0);
constraint.warm_start(
&mut body1,
&mut body2,
normal,
tangent_directions,
solver_config.warm_start_coefficient,
);
}
}
/// Solves contacts by iterating through the given contact constraints
/// and applying impulses to colliding rigid bodies.
///
/// This solve is done `iterations` times. With a substepped solver,
/// `iterations` should typically be `1`, as substeps will handle the iteration.
///
/// If `use_bias` is `true`, the impulses will be boosted to account for overlap.
/// The solver should often be run twice per frame or substep: first with the bias,
/// and then without it to *relax* the velocities and reduce overshooting caused by
/// [warm starting](SubstepSolverSet::WarmStart).
///
/// See [`SubstepSolverSet::SolveConstraints`] and [`SubstepSolverSet::Relax`] for more information.
#[allow(clippy::too_many_arguments)]
#[allow(clippy::type_complexity)]
fn solve_contacts(
bodies: &mut Query<RigidBodyQuery>,
constraints: &mut [ContactConstraint],
delta_secs: Scalar,
iterations: usize,
use_bias: bool,
max_overlap_solve_speed: Scalar,
) {
for _ in 0..iterations {
for constraint in &mut *constraints {
let Ok([mut body1, mut body2]) =
bodies.get_many_mut([constraint.entity1, constraint.entity2])
else {
continue;
};
constraint.solve(
&mut body1,
&mut body2,
delta_secs,
use_bias,
max_overlap_solve_speed,
);
}
}
}
/// Iterates through contact constraints and applies impulses to account for [`Restitution`].
///
/// Note that restitution with TGS Soft and speculative contacts may not be perfectly accurate.
/// This is a tradeoff, but cheap CCD is often more important than perfect restitution.
///
/// The number of iterations can be increased with [`SolverConfig::restitution_iterations`]
/// to apply restitution for multiple contact points more evenly.
#[allow(clippy::too_many_arguments)]
#[allow(clippy::type_complexity)]
fn solve_restitution(
mut bodies: Query<RigidBodyQuery>,
mut constraints: ResMut<ContactConstraints>,
solver_config: Res<SolverConfig>,
length_unit: Res<PhysicsLengthUnit>,
) {
// TODO: This could be configurable.
// The restitution threshold determining the speed required for restitution to be applied.
let threshold = solver_config.restitution_threshold * length_unit.0;
for constraint in constraints.iter_mut() {
let restitution = constraint.restitution.coefficient;
if restitution == 0.0 {
continue;
}
let Ok([mut body1, mut body2]) =
bodies.get_many_mut([constraint.entity1, constraint.entity2])
else {
continue;
};
// Performing multiple iterations can result in more accurate restitution,
// but only if there are more than one contact point.
let restitution_iterations = if constraint.points.len() > 1 {
solver_config.restitution_iterations
} else {
1
};
for _ in 0..restitution_iterations {
constraint.apply_restitution(&mut body1, &mut body2, threshold);
}
}
}
/// Copies contact impulses from [`ContactConstraints`] to the contacts in [`Collisions`].
/// They will be used for [warm starting](SubstepSolverSet::WarmStart).
fn store_contact_impulses(
constraints: Res<ContactConstraints>,
mut collisions: ResMut<Collisions>,
) {
for constraint in constraints.iter() {
let Some(contacts) =
collisions.get_mut(constraint.collider_entity1, constraint.collider_entity2)
else {
continue;
};
let manifold = &mut contacts.manifolds[constraint.manifold_index];
for (contact, constraint_point) in
manifold.contacts.iter_mut().zip(constraint.points.iter())
{
contact.normal_impulse = constraint_point.normal_part.impulse;
contact.tangent_impulse = constraint_point
.tangent_part
.as_ref()
.map_or(default(), |part| part.impulse);
}
}
}
/// Finalizes the positions of bodies by applying the [`AccumulatedTranslation`].
#[allow(clippy::type_complexity)]
fn apply_translation(
mut bodies: Query<
(
&RigidBody,
&mut Position,
&Rotation,
&PreviousRotation,
&mut AccumulatedTranslation,
&CenterOfMass,
),
Changed<AccumulatedTranslation>,
>,
) {
for (rb, mut pos, rot, prev_rot, mut translation, center_of_mass) in &mut bodies {
if rb.is_static() {
continue;
}
// We must also account for the translation caused by rotations around the center of mass,
// as it may be offset from `Position`.
pos.0 += crate::utils::get_pos_translation(&translation, prev_rot, rot, center_of_mass);
translation.0 = Vector::ZERO;
}
}
/// Applies velocity corrections caused by joint damping.
#[allow(clippy::type_complexity)]
pub fn joint_damping<T: Joint>(
mut bodies: Query<
(
&RigidBody,
&mut LinearVelocity,
&mut AngularVelocity,
&InverseMass,
Option<&Dominance>,
),
Without<Sleeping>,
>,
joints: Query<&T, Without<RigidBody>>,
time: Res<Time>,
) {
let delta_secs = time.delta_seconds_adjusted();
for joint in &joints {
if let Ok(
[(rb1, mut lin_vel1, mut ang_vel1, inv_mass1, dominance1), (rb2, mut lin_vel2, mut ang_vel2, inv_mass2, dominance2)],
) = bodies.get_many_mut(joint.entities())
{
let delta_omega =
(ang_vel2.0 - ang_vel1.0) * (joint.damping_angular() * delta_secs).min(1.0);
if rb1.is_dynamic() {
ang_vel1.0 += delta_omega;
}
if rb2.is_dynamic() {
ang_vel2.0 -= delta_omega;
}
let delta_v =
(lin_vel2.0 - lin_vel1.0) * (joint.damping_linear() * delta_secs).min(1.0);
let w1 = if rb1.is_dynamic() { inv_mass1.0 } else { 0.0 };
let w2 = if rb2.is_dynamic() { inv_mass2.0 } else { 0.0 };
if w1 + w2 <= Scalar::EPSILON {
continue;
}
let p = delta_v / (w1 + w2);
let dominance1 = dominance1.map_or(0, |dominance| dominance.0);
let dominance2 = dominance2.map_or(0, |dominance| dominance.0);
if rb1.is_dynamic() && (!rb2.is_dynamic() || dominance1 <= dominance2) {
lin_vel1.0 += p * inv_mass1.0;
}
if rb2.is_dynamic() && (!rb1.is_dynamic() || dominance2 <= dominance1) {
lin_vel2.0 -= p * inv_mass2.0;
}
}
}
}