bevy/crates/bevy_diagnostic/src/frame_time_diagnostics_plugin.rs
Christopher Durham c19aa5939d Add Exponential Moving Average into diagnostics (#4992)
# Objective

- Add Time-Adjusted Rolling EMA-based smoothing to diagnostics.
- Closes #4983; see that issue for more more information.

## Terms

- EMA - [Exponential Moving Average](https://en.wikipedia.org/wiki/Moving_average#Exponential_moving_average)
- SMA - [Simple Moving Average](https://en.wikipedia.org/wiki/Moving_average#Simple_moving_average)

## Solution

- We use a fairly standard approximation of a true EMA where $EMA_{\text{frame}} = EMA_{\text{previous}} + \alpha \left( x_{\text{frame}} - EMA_{\text{previous}} \right)$ where $\alpha = \Delta t / \tau$ and $\tau$ is an arbitrary smoothness factor. (See #4983 for more discussion of the math.)
- The smoothness factor is here defaulted to $2 / 21$; this was chosen fairly arbitrarily as supposedly related to the existing 20-bucket SMA.
- The smoothness factor can be set on a per-diagnostic basis via `Diagnostic::with_smoothing_factor`.

---

## Changelog

### Added

- `Diagnostic::smoothed` - provides an exponentially smoothed view of a recorded diagnostic, to e.g. reduce jitter in frametime readings.

### Changed
- `LogDiagnosticsPlugin` now records the smoothed value rather than the raw value.
  - For diagnostics recorded less often than every 0.1 seconds, this change to defaults will have no visible effect.
  - For discrete diagnostics where this smoothing is not desirable, set a smoothing factor of 0 to disable smoothing.
  - The average of the recent history is still shown when available.
2022-10-24 13:46:37 +00:00

48 lines
1.7 KiB
Rust

use crate::{Diagnostic, DiagnosticId, Diagnostics};
use bevy_app::prelude::*;
use bevy_core::FrameCount;
use bevy_ecs::system::{Res, ResMut};
use bevy_time::Time;
/// Adds "frame time" diagnostic to an App, specifically "frame time", "fps" and "frame count"
#[derive(Default)]
pub struct FrameTimeDiagnosticsPlugin;
impl Plugin for FrameTimeDiagnosticsPlugin {
fn build(&self, app: &mut bevy_app::App) {
app.add_startup_system(Self::setup_system)
.add_system(Self::diagnostic_system);
}
}
impl FrameTimeDiagnosticsPlugin {
pub const FPS: DiagnosticId = DiagnosticId::from_u128(288146834822086093791974408528866909483);
pub const FRAME_COUNT: DiagnosticId =
DiagnosticId::from_u128(54021991829115352065418785002088010277);
pub const FRAME_TIME: DiagnosticId =
DiagnosticId::from_u128(73441630925388532774622109383099159699);
pub fn setup_system(mut diagnostics: ResMut<Diagnostics>) {
diagnostics.add(Diagnostic::new(Self::FRAME_TIME, "frame_time", 20).with_suffix("ms"));
diagnostics.add(Diagnostic::new(Self::FPS, "fps", 20));
diagnostics
.add(Diagnostic::new(Self::FRAME_COUNT, "frame_count", 1).with_smoothing_factor(0.0));
}
pub fn diagnostic_system(
mut diagnostics: ResMut<Diagnostics>,
time: Res<Time>,
frame_count: Res<FrameCount>,
) {
diagnostics.add_measurement(Self::FRAME_COUNT, || frame_count.0 as f64);
let delta_seconds = time.raw_delta_seconds_f64();
if delta_seconds == 0.0 {
return;
}
diagnostics.add_measurement(Self::FRAME_TIME, || delta_seconds * 1000.0);
diagnostics.add_measurement(Self::FPS, || 1.0 / delta_seconds);
}
}