Struct Physics

pub struct Physics { /* private fields */ }

The clock representing physics time, following the Time clock used by the schedule that physics runs in.

In FixedPostUpdate and other fixed schedules, this uses Time<Fixed>, while in schedules such as Update, a variable timestep following Time<Virtual> is used.

Time<Physics> is automatically set as the generic Time resource for the PhysicsSchedule.

Usage

Physics Speed

The relative speed of Time<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.

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 Physics: Any + Send + Sync, bool: FromReflect + TypePath + MaybeTyped + RegisterForReflection, f64: FromReflect + TypePath + MaybeTyped + RegisterForReflection,

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

Constructs a concrete instance of Self from a reflected value.

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

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

impl GetTypeRegistration for Physics

where Physics: Any + Send + Sync, bool: FromReflect + TypePath + MaybeTyped + RegisterForReflection, f64: FromReflect + TypePath + MaybeTyped + 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

Tests for self and other values to be equal, and is used by ==.

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

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

impl PartialReflect for Physics

where Physics: Any + Send + Sync, bool: FromReflect + TypePath + MaybeTyped + RegisterForReflection, f64: FromReflect + TypePath + MaybeTyped + RegisterForReflection,

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

Returns the TypeInfo of the type represented by this value.

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

Clones the value as a Reflect trait object.

fn try_apply(&mut self, value: &dyn PartialReflect) -> 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 try_into_reflect( self: Box<Self>, ) -> Result<Box<dyn Reflect>, Box<dyn PartialReflect>>

Attempts to cast this type to a boxed, fully-reflected value.

fn try_as_reflect(&self) -> Option<&dyn Reflect>

Attempts to cast this type to a fully-reflected value.

fn try_as_reflect_mut(&mut self) -> Option<&mut dyn Reflect>

Attempts to cast this type to a mutable, fully-reflected value.

fn into_partial_reflect(self: Box<Self>) -> Box<dyn PartialReflect>

Casts this type to a boxed, reflected value.

fn as_partial_reflect(&self) -> &dyn PartialReflect

Casts this type to a reflected value.

fn as_partial_reflect_mut(&mut self) -> &mut dyn PartialReflect

Casts this type to a mutable, reflected value.

fn reflect_partial_eq(&self, value: &dyn PartialReflect) -> 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 PartialReflect + '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 Reflect for Physics

where Physics: Any + Send + Sync, bool: FromReflect + TypePath + MaybeTyped + RegisterForReflection, f64: FromReflect + TypePath + MaybeTyped + RegisterForReflection,

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, fully-reflected value.

fn as_reflect(&self) -> &dyn Reflect

Casts this type to a fully-reflected value.

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

Casts this type to a mutable, fully-reflected value.

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

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

impl Struct for Physics

where Physics: Any + Send + Sync, bool: FromReflect + TypePath + MaybeTyped + RegisterForReflection, f64: FromReflect + TypePath + MaybeTyped + RegisterForReflection,

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

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

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

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

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

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

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

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

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.

fn get_represented_struct_info(&self) -> Option<&'static StructInfo>

Will return None if TypeInfo is not available.

impl TypePath for Physics

where Physics: 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 Physics: Any + Send + Sync, bool: FromReflect + TypePath + MaybeTyped + RegisterForReflection, f64: FromReflect + TypePath + MaybeTyped + RegisterForReflection,

fn type_info() -> &'static TypeInfo

Returns the compile-time info for the underlying type.

impl Copy for Physics

impl StructuralPartialEq for Physics