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use amethyst_core::{
AccessorCow, BatchAccessor, BatchController, BatchUncheckedWorld, Dispatcher, ReadExpect,
RunningTime, System, World,
use crate::{PhysicsTime, PtReal};
/// This `Batch` is a used to dispatch the physics `System`s.
/// Depending on the `PhysicsTime::_time_bank` value, could be necessary run the stepping, multiple
/// times on the same frame.
/// Each frame, to the `_time_bank` is added the frame _delta time_ (which is variable).
/// Sometimes, could happens that the `Timer::delta_time` is so big that too much sub steps have to
/// be processed in order to consume the `_time_bank`.
/// This process, will increase the delta time of the next frame, entering so
/// in a spiral that will drop the performances.
/// To break this behavior a fall back algorithm, will clamp the maximum size of the `_time_bank`.
/// You can control the maximum `_time_bank` by changing the `max_sub_steps`.
pub struct PhysicsBatchSystem<'a, 'b, N: crate::PtReal> {
accessor: BatchAccessor,
dispatcher: Dispatcher<'a, 'b>,
phantom_data: std::marker::PhantomData<N>,
impl<'a, 'b, N: PtReal> BatchController<'a, 'b> for PhysicsBatchSystem<'a, 'b, N> {
type BatchSystemData = (ReadExpect<'a, PhysicsTime>, ReadExpect<'a, Time>);
unsafe fn create(accessor: BatchAccessor, dispatcher: Dispatcher<'a, 'b>) -> Self {
PhysicsBatchSystem {
phantom_data: std::marker::PhantomData,
impl<'a, N: PtReal> System<'a> for PhysicsBatchSystem<'_, '_, N> {
type SystemData = BatchUncheckedWorld<'a>;
fn run(&mut self, data: Self::SystemData) {
let iterations = {
let time = data.0.fetch::<Time>();
let mut physics_time = data.0.fetch_mut::<PhysicsTime>();
physics_time.in_sub_step = true;
physics_time._time_bank += time.delta_seconds();
// Avoid spiral performance degradation
physics_time._time_bank = physics_time._time_bank.min(physics_time._max_bank_size);
let iterations = (physics_time._time_bank / physics_time.delta_seconds).trunc();
physics_time._time_bank -= iterations * physics_time.delta_seconds;
iterations as i32
for _i in 0..iterations {
let mut physics_time = data.0.fetch_mut::<PhysicsTime>();
physics_time.in_sub_step = false;
fn running_time(&self) -> RunningTime {
fn accessor<'c>(&'c self) -> AccessorCow<'a, 'c, Self> {
fn setup(&mut self, world: &mut World) {
unsafe impl<N: PtReal> Send for PhysicsBatchSystem<'_, '_, N> {}
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