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use bevy::{
prelude::*,
render::{RenderApp, RenderStage, RenderWorld},
winit::WinitWindows,
};
use std::time::{Duration, Instant};
#[derive(Debug, Clone, Component)]
pub struct FramepacePlugin {
pub enabled: bool,
pub framerate_limit: FramerateLimit,
pub safety_margin: Duration,
}
impl Plugin for FramepacePlugin {
fn build(&self, app: &mut App) {
app.insert_resource(self.clone())
.insert_resource(MeasuredFramerateLimit(0))
.add_system_to_stage(CoreStage::Update, measure_refresh_rate);
app.sub_app_mut(RenderApp)
.insert_resource(FrameTimer::default())
.add_system_to_stage(RenderStage::Extract, extract_refresh_rate)
.add_system_to_stage(RenderStage::Render, framerate_exact_limiter)
.add_system_to_stage(RenderStage::Cleanup, framerate_limit_forward_estimator);
}
}
impl Default for FramepacePlugin {
fn default() -> Self {
Self {
enabled: true,
framerate_limit: FramerateLimit::Auto,
safety_margin: Duration::from_micros(500),
}
}
}
impl FramepacePlugin {
pub fn framerate(fps: u64) -> Self {
Self {
framerate_limit: FramerateLimit::Manual(fps),
..Default::default()
}
}
}
#[derive(Debug, Clone)]
pub enum FramerateLimit {
Auto,
Manual(u64),
}
#[derive(Debug, Clone, Component)]
pub struct MeasuredFramerateLimit(u64);
#[derive(Debug)]
struct FrameTimer {
post_render_start: Instant,
render_start: Instant,
exact_sleep: Duration,
}
impl Default for FrameTimer {
fn default() -> Self {
FrameTimer {
post_render_start: Instant::now(),
render_start: Instant::now(),
exact_sleep: Duration::from_millis(0),
}
}
}
fn measure_refresh_rate(
settings: Res<FramepacePlugin>,
winit: Res<WinitWindows>,
windows: Res<Windows>,
mut meas_limit: ResMut<MeasuredFramerateLimit>,
) {
if !windows.is_changed() && !settings.is_changed() && !winit.is_changed() {
return;
}
let update = match settings.framerate_limit {
FramerateLimit::Auto => {
let modes = winit
.get_window(windows.get_primary().unwrap().id())
.unwrap()
.current_monitor()
.unwrap()
.video_modes();
let best = modes.map(|f| f.refresh_rate() as u64).max();
if let Some(framerate) = best {
if framerate != meas_limit.0 {
Some(framerate)
} else {
None
}
} else {
None
}
}
FramerateLimit::Manual(framerate) => {
if framerate != meas_limit.0 {
Some(framerate)
} else {
None
}
}
};
if let Some(fps) = update {
*meas_limit = MeasuredFramerateLimit(fps);
info!("Detected refresh rate is: {} fps", fps);
}
}
fn extract_refresh_rate(
settings: Res<FramepacePlugin>,
framerate_limit: Res<MeasuredFramerateLimit>,
mut r_world: ResMut<RenderWorld>,
) {
r_world.insert_resource(framerate_limit.clone());
r_world.insert_resource(settings.clone());
}
fn framerate_limit_forward_estimator(
mut timer: ResMut<FrameTimer>,
settings: Res<FramepacePlugin>,
refresh_rate: Res<MeasuredFramerateLimit>,
) {
let framerate_limit = refresh_rate.0;
let render_end = Instant::now();
let target_frametime = Duration::from_micros(1_000_000 / framerate_limit);
let last_frametime = render_end.duration_since(timer.post_render_start);
let last_render_time = last_frametime - timer.exact_sleep;
let estimated_cpu_time_needed = last_render_time + settings.safety_margin;
let estimated_sleep_time = target_frametime - target_frametime.min(estimated_cpu_time_needed);
if settings.enabled {
spin_sleep::sleep(estimated_sleep_time);
}
timer.post_render_start = Instant::now();
}
fn framerate_exact_limiter(
mut timer: ResMut<FrameTimer>,
settings: Res<FramepacePlugin>,
refresh_rate: Res<MeasuredFramerateLimit>,
) {
let framerate_limit = refresh_rate.0;
let system_start = Instant::now();
let target_frametime = Duration::from_micros(1_000_000 / framerate_limit);
let this_frametime = system_start.duration_since(timer.render_start);
let sleep_needed = target_frametime - target_frametime.min(this_frametime);
let sleep_needed_safe =
sleep_needed.max(Duration::from_micros(500)) - Duration::from_micros(500);
if settings.enabled {
spin_sleep::sleep(sleep_needed_safe);
}
if sleep_needed.is_zero() {
warn!(
"Frame dropped. Frametime: {:.2?} (+{})",
this_frametime,
format!(
"{:.2}ms",
(this_frametime - target_frametime).as_micros() as f32 / 1000.0
),
);
}
timer.render_start = Instant::now();
timer.exact_sleep = timer.render_start.duration_since(system_start);
}