Struct avian3d::schedule::Physics

pub struct Physics { /* private fields */ }

The clock representing physics time, following Time<Real>. Can be configured to use a fixed or variable timestep.

The clock is automatically set as the generic Time resource for the PhysicsSchedule.

By default, a fixed timestep of 60 Hz is used.

Usage

The timestep used for advancing the simulation can be configured by overwriting the Time<Physics> resource:

use avian3d::prelude::*;
use bevy::{prelude::*, utils::Duration};

fn main() {
    App::new()
        .add_plugins((DefaultPlugins, PhysicsPlugins::default()))
        .insert_resource(Time::new_with(Physics::fixed_hz(144.0)))
        .run();
}

In the PhysicsSchedule, the generic Time resource is automatically replaced by Time<Physics>, so time works in a unified way across schedules:

// In `Update`, `Time` is `Time<Virtual>`, but in `PhysicsSchedule` it's `Time<Physics>`
fn print_delta_time(time: Res<Time>) {
    println!("{}", time.delta_seconds());
}

Physics speed

The relative speed of physics can be configured at startup using with_relative_speed or when the app is running using set_relative_speed:

use avian3d::prelude::*;
use bevy::{prelude::*, utils::Duration};

fn main() {
    App::new()
        .add_plugins((DefaultPlugins, PhysicsPlugins::default()))
        // Run physics at 0.5 speed
        .insert_resource(Time::<Physics>::default().with_relative_speed(0.5))
        .run();
}

Pausing, resuming and stepping physics

Time<Physics> can be used to pause and resume the simulation:

use avian3d::prelude::*;
use bevy::prelude::*;

fn pause(mut time: ResMut<Time<Physics>>) {
    time.pause();
}

fn unpause(mut time: ResMut<Time<Physics>>) {
    time.unpause();
}

To advance the simulation by a certain amount of time instantly, you can advance the Time<Physics> clock and manually run the PhysicsSchedule in an exclusive system:

use avian3d::prelude::*;
use bevy::{prelude::*, utils::Duration};

fn run_physics(world: &mut World) {
    // Advance the simulation by 10 steps at 120 Hz
    for _ in 0..10 {
        world
            .resource_mut::<Time<Physics>>()
            .advance_by(Duration::from_secs_f64(1.0 / 120.0));
        world.run_schedule(PhysicsSchedule);
    }
}

When to multiply by delta time?

Schedules like Update use a variable timestep, which can often cause frame rate dependent behavior when moving bodies. One way to help address the issue is by multiplying by delta time.

In general, if you’re doing a continuous operation, you should always multiply by delta time, but for instantaneous operations it’s not necessary.

Continuous operations move or accelerate bodies over time:

// Move continuously over time
position += velocity * delta_time;
// Accelerate continuously
velocity += acceleration * delta_time;

Instantaneous operations apply a singular sudden burst of velocity or set it to a specific value:

// Apply a burst of speed once (jumps, explosions and so on)
velocity += impulse;
// Set velocity to a specific value
velocity = target_velocity;

For systems using a fixed timestep, using delta time is not necessary for frame rate independence, but it’s still recommended so that the physical units are more logical.

Implementations

impl Physics

pub const fn from_timestep(timestep_mode: TimestepMode) -> Self

Creates a new Physics clock with the given type of timestep.

pub fn fixed_hz(hz: f64) -> Self

Returns a new Time<Physics> clock with a TimestepMode::Fixed using the given frequency in Hertz (1/second).

Panics

Panics if hz is zero, negative or not finite.

pub fn fixed_once_hz(hz: f64) -> Self

Returns a new Time<Physics> clock with a TimestepMode::FixedOnce using the given frequency in Hertz (1/second).

Unlike with TimestepMode::Fixed, the PhysicsSchedule will only be run once per frame instead of accumulating time and running physics until the accumulator has been consumed. This can be useful for server usage where the server and client must be kept in sync.

Panics

Panics if hz is zero, negative or not finite.

pub fn variable(max_delta_seconds: f64) -> Self

Returns a new Time<Physics> clock with a TimestepMode::Variable using the given maximum duration that the simulation can be advanced by during a single frame in seconds.

Panics

Panics if max_delta_seconds is zero or negative.

Trait Implementations

impl Clone for Physics

fn clone(&self) -> Physics

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Physics

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for Physics

fn default() -> Self

Returns the “default value” for a type.

impl FromReflect for Physics

where Self: Any + Send + Sync, TimestepMode: FromReflect + TypePath + RegisterForReflection, bool: FromReflect + TypePath + RegisterForReflection, f64: FromReflect + TypePath + RegisterForReflection,

fn from_reflect(reflect: &dyn Reflect) -> Option<Self>

Constructs a concrete instance of Self from a reflected value.

fn take_from_reflect( reflect: Box<dyn Reflect> ) -> Result<Self, Box<dyn Reflect>>

Attempts to downcast the given value to Self using, constructing the value using from_reflect if that fails.

impl GetTypeRegistration for Physics

where Self: Any + Send + Sync, TimestepMode: FromReflect + TypePath + RegisterForReflection, bool: FromReflect + TypePath + RegisterForReflection, f64: FromReflect + TypePath + RegisterForReflection,

fn get_type_registration() -> TypeRegistration

Returns the default TypeRegistration for this type.

fn register_type_dependencies(registry: &mut TypeRegistry)

Registers other types needed by this type.

impl PartialEq for Physics

fn eq(&self, other: &Physics) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Reflect for Physics

where Self: Any + Send + Sync, TimestepMode: FromReflect + TypePath + RegisterForReflection, bool: FromReflect + TypePath + RegisterForReflection, f64: FromReflect + TypePath + RegisterForReflection,

fn get_represented_type_info(&self) -> Option<&'static TypeInfo>

Returns the TypeInfo of the type represented by this value.

fn into_any(self: Box<Self>) -> Box<dyn Any>

Returns the value as a Box<dyn Any>.

fn as_any(&self) -> &dyn Any

Returns the value as a &dyn Any.

fn as_any_mut(&mut self) -> &mut dyn Any

Returns the value as a &mut dyn Any.

fn into_reflect(self: Box<Self>) -> Box<dyn Reflect>

Casts this type to a boxed reflected value.

fn as_reflect(&self) -> &dyn Reflect

Casts this type to a reflected value.

fn as_reflect_mut(&mut self) -> &mut dyn Reflect

Casts this type to a mutable reflected value.

fn clone_value(&self) -> Box<dyn Reflect>

Clones the value as a Reflect trait object.

fn set(&mut self, value: Box<dyn Reflect>) -> Result<(), Box<dyn Reflect>>

Performs a type-checked assignment of a reflected value to this value.

fn try_apply(&mut self, value: &dyn Reflect) -> Result<(), ApplyError>

Tries to apply a reflected value to this value.

fn reflect_kind(&self) -> ReflectKind

Returns a zero-sized enumeration of “kinds” of type.

fn reflect_ref(&self) -> ReflectRef<'_>

Returns an immutable enumeration of “kinds” of type.

fn reflect_mut(&mut self) -> ReflectMut<'_>

Returns a mutable enumeration of “kinds” of type.

fn reflect_owned(self: Box<Self>) -> ReflectOwned

Returns an owned enumeration of “kinds” of type.

fn reflect_partial_eq(&self, value: &dyn Reflect) -> Option<bool>

Returns a “partial equality” comparison result.

fn debug(&self, f: &mut Formatter<'_>) -> Result

Debug formatter for the value.

fn apply(&mut self, value: &(dyn Reflect + 'static))

Applies a reflected value to this value.

fn reflect_hash(&self) -> Option<u64>

Returns a hash of the value (which includes the type).

fn serializable(&self) -> Option<Serializable<'_>>

Returns a serializable version of the value.

fn is_dynamic(&self) -> bool

Indicates whether or not this type is a dynamic type.

impl Struct for Physics

where Self: Any + Send + Sync, TimestepMode: FromReflect + TypePath + RegisterForReflection, bool: FromReflect + TypePath + RegisterForReflection, f64: FromReflect + TypePath + RegisterForReflection,

fn field(&self, name: &str) -> Option<&dyn Reflect>

Returns a reference to the value of the field named name as a &dyn Reflect.

fn field_mut(&mut self, name: &str) -> Option<&mut dyn Reflect>

Returns a mutable reference to the value of the field named name as a &mut dyn Reflect.

fn field_at(&self, index: usize) -> Option<&dyn Reflect>

Returns a reference to the value of the field with index index as a &dyn Reflect.

fn field_at_mut(&mut self, index: usize) -> Option<&mut dyn Reflect>

Returns a mutable reference to the value of the field with index index as a &mut dyn Reflect.

fn name_at(&self, index: usize) -> Option<&str>

Returns the name of the field with index index.

fn field_len(&self) -> usize

Returns the number of fields in the struct.

fn iter_fields(&self) -> FieldIter<'_>

Returns an iterator over the values of the reflectable fields for this struct.

fn clone_dynamic(&self) -> DynamicStruct

Clones the struct into a DynamicStruct.

impl TypePath for Physics

where Self: Any + Send + Sync,

fn type_path() -> &'static str

Returns the fully qualified path of the underlying type.

fn short_type_path() -> &'static str

Returns a short, pretty-print enabled path to the type.

fn type_ident() -> Option<&'static str>

Returns the name of the type, or None if it is anonymous.

fn crate_name() -> Option<&'static str>

Returns the name of the crate the type is in, or None if it is anonymous.

fn module_path() -> Option<&'static str>

Returns the path to the module the type is in, or None if it is anonymous.

impl Typed for Physics

where Self: Any + Send + Sync, TimestepMode: FromReflect + TypePath + RegisterForReflection, bool: FromReflect + TypePath + RegisterForReflection, f64: FromReflect + TypePath + RegisterForReflection,

fn type_info() -> &'static TypeInfo

Returns the compile-time info for the underlying type.

impl Copy for Physics

impl StructuralPartialEq for Physics