Add LinearDamping and AngularDamping

src/components/mod.rs

@@ -500,6 +500,26 @@ impl From<Scalar> for Friction {
  }
 }
 
+/// Automatically slows down a dynamic [rigid body](RigidBody), decreasing it's [linear velocity](LinearVelocity)
+/// each frame. This can be used to simulate air resistance.
+///
+/// The default linear damping coefficient is `0.0`, which corresponds to no damping.
+#[derive(
+ Component, Reflect, Debug, Clone, Copy, PartialEq, PartialOrd, Default, Deref, DerefMut,
+)]
+#[reflect(Component)]
+pub struct LinearDamping(pub Scalar);
+
+/// Automatically slows down a dynamic [rigid body](RigidBody), decreasing it's [angular velocity](AngularVelocity)
+/// each frame. This can be used to simulate air resistance.
+///
+/// The default angular damping coefficient is `0.0`, which corresponds to no damping.
+#[derive(
+ Component, Reflect, Debug, Clone, Copy, PartialEq, PartialOrd, Default, Deref, DerefMut,
+)]
+#[reflect(Component)]
+pub struct AngularDamping(pub Scalar);
+
 #[cfg(test)]
 mod tests {
  use crate::prelude::*;

src/lib.rs

@@ -26,6 +26,7 @@
 //! - [Sensor colliders](Sensor)
 //! - [Collision layers](CollisionLayers)
 //! - Material properties like [restitution](Restitution) and [friction](Friction)
+//! - [Linear damping](LinearDamping) and [angular damping](AngularDamping) for simulating drag
 //! - External [forces](ExternalForce) and [torque](ExternalTorque)
 //! - [Gravity](Gravity)
 //! - [Joints](joints)

src/plugins/integrator.rs

@@ -28,6 +28,7 @@ type PosIntegrationComponents = (
  &'static mut Position,
  &'static mut PreviousPosition,
  &'static mut LinearVelocity,
+ Option<&'static LinearDamping>,
  &'static ExternalForce,
  &'static Mass,
 );
@@ -38,15 +39,20 @@ fn integrate_pos(
  gravity: Res<Gravity>,
  sub_dt: Res<SubDeltaTime>,
 ) {
- for (rb, mut pos, mut prev_pos, mut lin_vel, external_force, mass) in &mut bodies {
+ for (rb, mut pos, mut prev_pos, mut lin_vel, lin_damping, external_force, mass) in &mut bodies {
  prev_pos.0 = pos.0;
 
  if rb.is_static() {
  continue;
  }
 
- // Apply gravity and other external forces
+ // Apply damping, gravity and other external forces
  if rb.is_dynamic() {
+ // Apply damping
+ if let Some(damping) = lin_damping {
+ lin_vel.0 *= 1.0 / (1.0 + sub_dt.0 * damping.0);
+ }
+
  let gravitation_force = mass.0 * gravity.0;
  let external_forces = gravitation_force + external_force.0;
  lin_vel.0 += sub_dt.0 * external_forces / mass.0;
@@ -61,6 +67,7 @@ type RotIntegrationComponents = (
  &'static mut Rotation,
  &'static mut PreviousRotation,
  &'static mut AngularVelocity,
+ Option<&'static AngularDamping>,
  &'static ExternalTorque,
  &'static Inertia,
  &'static InverseInertia,
@@ -72,17 +79,30 @@ fn integrate_rot(
  mut bodies: Query<RotIntegrationComponents, Without<Sleeping>>,
  sub_dt: Res<SubDeltaTime>,
 ) {
- for (rb, mut rot, mut prev_rot, mut ang_vel, external_torque, _inertia, inverse_inertia) in
- &mut bodies
+ for (
+ rb,
+ mut rot,
+ mut prev_rot,
+ mut ang_vel,
+ ang_damping,
+ external_torque,
+ _inertia,
+ inverse_inertia,
+ ) in &mut bodies
  {
  prev_rot.0 = *rot;
 
  if rb.is_static() {
  continue;
  }
 
- // Apply external torque
+ // Apply damping and external torque
  if rb.is_dynamic() {
+ // Apply damping
+ if let Some(damping) = ang_damping {
+ ang_vel.0 *= 1.0 / (1.0 + sub_dt.0 * damping.0);
+ }
+
  ang_vel.0 += sub_dt.0 * inverse_inertia.0 * external_torque.0;
  }
 
@@ -96,17 +116,30 @@ fn integrate_rot(
  mut bodies: Query<RotIntegrationComponents, Without<Sleeping>>,
  sub_dt: Res<SubDeltaTime>,
 ) {
- for (rb, mut rot, mut prev_rot, mut ang_vel, external_torque, inertia, inverse_inertia) in
- &mut bodies
+ for (
+ rb,
+ mut rot,
+ mut prev_rot,
+ mut ang_vel,
+ ang_damping,
+ external_torque,
+ inertia,
+ inverse_inertia,
+ ) in &mut bodies
  {
  prev_rot.0 = *rot;
 
  if rb.is_static() {
  continue;
  }
 
- // Apply external torque
+ // Apply damping and external torque
  if rb.is_dynamic() {
+ // Apply damping
+ if let Some(damping) = ang_damping {
+ ang_vel.0 *= 1.0 / (1.0 + sub_dt.0 * damping.0);
+ }
+
  let delta_ang_vel = sub_dt.0
  * inverse_inertia.rotated(&rot).0
  * (external_torque.0 - ang_vel.0.cross(inertia.rotated(&rot).0 * ang_vel.0));

src/plugins/setup.rs

@@ -64,6 +64,8 @@ impl Plugin for PhysicsSetupPlugin {
  .register_type::<PreSolveAngularVelocity>()
  .register_type::<Restitution>()
  .register_type::<Friction>()
+ .register_type::<LinearDamping>()
+ .register_type::<AngularDamping>()
  .register_type::<ExternalForce>()
  .register_type::<ExternalTorque>()
  .register_type::<Mass>()