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use bevy::prelude::*;
use std::mem;
use std::mem::MaybeUninit;
const MAX_INTERVAL: usize = 64;
type BoxedSystem = Box<dyn FnOnce(&mut World) + Send + Sync>;
struct TimingWheel {
current_tick: usize,
ring: [Vec<(usize, BoxedSystem)>; MAX_INTERVAL],
}
impl Default for TimingWheel {
fn default() -> Self {
let mut empty = MaybeUninit::<[Vec<_>; MAX_INTERVAL]>::uninit();
let p: *mut Vec<BoxedSystem> = unsafe { mem::transmute(&mut empty) };
for i in 0..MAX_INTERVAL {
unsafe {
p.add(i).write(vec![]);
}
}
TimingWheel {
current_tick: 0,
ring: unsafe { empty.assume_init() },
}
}
}
impl TimingWheel {
fn schedule(&mut self, offset: usize, ticks: usize, timer: BoxedSystem) {
self.ring[offset].push((ticks, timer));
}
fn tick(&mut self) -> Vec<(usize, BoxedSystem)> {
let timers = mem::take(&mut self.ring[self.current_tick]);
self.current_tick = (self.current_tick + 1) % MAX_INTERVAL;
timers
}
}
#[derive(Default)]
pub struct Timers {
level: [TimingWheel; 4],
}
impl Timers {
pub fn after<S>(&mut self, after: usize, timer: S)
where
S: FnOnce(&mut World) + Send + Sync + 'static,
{
let ticks = after
+ self.level[0].current_tick
+ (self.level[1].current_tick << 6)
+ (self.level[2].current_tick << 12)
+ (self.level[3].current_tick << 18);
let level = if ticks == 0 {
0
} else {
(63 - ticks.leading_zeros()) / 6
};
match level {
0 => self.level[0].schedule(ticks, 0, Box::new(timer)),
1 => self.level[1].schedule((ticks >> 6) - 1, ticks & 0b111111, Box::new(timer)),
2 => self.level[2].schedule((ticks >> 12) - 1, ticks & 0b111111111111, Box::new(timer)),
3 => self.level[3].schedule(
(ticks >> 18) - 1,
ticks & 0b111111111111111111,
Box::new(timer),
),
_ => panic!("timer interval too long"),
}
}
pub fn now<S>(&mut self, timer: S)
where
S: FnOnce(&mut World) + Send + Sync + 'static,
{
self.after(0, timer);
}
fn tick(&mut self) -> Vec<BoxedSystem> {
let v = self.level[0].tick().into_iter().map(|(_, x)| x).collect();
if self.level[0].current_tick == 63 {
for (tick, timer) in self.level[1].tick() {
self.level[0].schedule(tick, 0, timer);
}
if self.level[1].current_tick == 63 {
for (tick, timer) in self.level[2].tick() {
self.level[1].schedule((tick >> 6) - 1, tick & 0b111111, timer);
}
if self.level[2].current_tick == 63 {
for (tick, timer) in self.level[3].tick() {
self.level[2].schedule((tick >> 6) - 1, tick & 0b111111111111, timer);
}
}
}
}
v
}
}
#[derive(Default)]
struct RunTimers;
impl Stage for RunTimers {
fn run(&mut self, world: &mut World) {
let timers = world.get_resource_mut::<Timers>().expect("Failed").tick();
for timer in timers {
timer(world);
}
}
}
pub struct TimerPlugin;
impl Plugin for TimerPlugin {
fn build(&self, app: &mut App) {
app.world.insert_resource(Timers::default());
app.add_stage("run_timers", RunTimers);
}
}