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use std::time::{Duration, Instant};
/// Number of fps samples to store
const MAX_SAMPLES: usize = 100;
/// Keeps track of frame intervals and FPS
pub struct Timer {
start: Instant,
since_start: Duration,
previous: Instant,
tick_index: usize,
tick_sum: Duration,
tick_list: Box<[Duration; MAX_SAMPLES]>,
frame: u32,
}
impl Timer {
pub fn new() -> Self {
let start = Instant::now();
let since_start = Duration::ZERO;
let previous = start;
let tick_index = 0usize;
let tick_sum = Duration::ZERO;
let tick_list = Box::new([tick_sum; MAX_SAMPLES]);
let frame = 0u32;
Self {
start,
since_start,
previous,
tick_index,
tick_sum,
tick_list,
frame,
}
}
pub fn update(&mut self) {
let time = self.previous.elapsed();
self.previous = Instant::now();
// caculate average tick
self.tick_index += 1;
self.tick_index %= MAX_SAMPLES;
self.tick_sum -= self.tick_list[self.tick_index];
self.tick_sum += time;
self.tick_list[self.tick_index] = time;
// update frame count
self.frame += 1;
// update since
self.since_start = self.previous.duration_since(self.start);
}
pub const fn frame(&self) -> u32 {
self.frame
}
#[expect(clippy::cast_possible_truncation)]
pub const fn fps(&self) -> u32 {
match self.frame_time().as_nanos() {
0 => u32::MAX,
// fps can never be bigger than u32::MAX since we're
// computing in nanoseconds
nanos => 1_000_000_000u128.div_ceil(nanos) as u32,
}
}
#[expect(clippy::cast_possible_truncation)]
pub const fn frame_time(&self) -> Duration {
match self.tick_sum.checked_div(MAX_SAMPLES as u32) {
Some(duration) => duration,
None => Duration::ZERO,
}
}
pub const fn delta_time(&self) -> Duration {
self.tick_list[self.tick_index]
}
pub const fn since_start(&self) -> Duration {
self.since_start
}
}
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