Trim cosmic-text's shape run cache

crates/bevy_text/src/lib.rs

@@ -121,7 +121,8 @@ impl Plugin for TextPlugin {
  .ambiguous_with(CameraUpdateSystem),
  remove_dropped_font_atlas_sets,
  ),
- );
+ )
+ .add_systems(Last, trim_cosmic_cache);
 
  if let Some(render_app) = app.get_sub_app_mut(RenderApp) {
  render_app.add_systems(

crates/bevy_text/src/pipeline.rs

@@ -1,7 +1,12 @@
 use std::sync::Arc;
 
 use bevy_asset::{AssetId, Assets};
-use bevy_ecs::{component::Component, entity::Entity, reflect::ReflectComponent, system::Resource};
+use bevy_ecs::{
+ component::Component,
+ entity::Entity,
+ reflect::ReflectComponent,
+ system::{ResMut, Resource},
+};
 use bevy_math::{UVec2, Vec2};
 use bevy_reflect::{std_traits::ReflectDefault, Reflect};
 use bevy_render::texture::Image;
@@ -407,3 +412,11 @@ fn buffer_dimensions(buffer: &Buffer) -> Vec2 {
 
  Vec2::new(width.ceil(), height).ceil()
 }
+
+/// Discards cached shaped older than one tick.
+///
+/// We assume only text updated every tick benefits from the shape cache (e.g. animated text, or
+/// text that is dynamically measured for UI).
+pub(crate) fn trim_cosmic_cache(mut pipeline: ResMut<TextPipeline>) {
+ pipeline.font_system_mut().shape_run_cache.trim(2);
+}

examples/ui/text_debug.rs

@@ -1,5 +1,7 @@
 //! Shows various text layout options.
 
+use std::{collections::VecDeque, time::Duration};
+
 use bevy::{
  color::palettes::css::*,
  diagnostic::{DiagnosticsStore, FrameTimeDiagnosticsPlugin},
@@ -154,7 +156,15 @@ fn infotext_system(mut commands: Commands, asset_server: Res<AssetServer>) {
  builder.spawn((
  TextBundle::from_sections([
  TextSection::new(
- "This text changes in the bottom right",
+ "",
+ TextStyle {
+ font: font.clone(),
+ font_size: 25.0,
+ ..default()
+ },
+ ),
+ TextSection::new(
+ "\nThis text changes in the bottom right",
  TextStyle {
  font: font.clone(),
  font_size: 25.0,
@@ -223,10 +233,23 @@ fn infotext_system(mut commands: Commands, asset_server: Res<AssetServer>) {
 }
 
 fn change_text_system(
+ mut fps_history: Local<VecDeque<f64>>,
+ mut time_history: Local<VecDeque<Duration>>,
  time: Res<Time>,
  diagnostics: Res<DiagnosticsStore>,
  mut query: Query<&mut Text, With<TextChanges>>,
 ) {
+ time_history.push_front(time.elapsed());
+ time_history.truncate(120);
+ let avg_fps = (time_history.len() as f64)
+ / (time_history.front().copied().unwrap_or_default()
+ - time_history.back().copied().unwrap_or_default())
+ .as_secs_f64()
+ .max(0.0001);
+ fps_history.push_front(avg_fps);
+ fps_history.truncate(120);
+ let fps_variance = std_deviation(fps_history.make_contiguous()).unwrap_or_default();
+
  for mut text in &mut query {
  let mut fps = 0.0;
  if let Some(fps_diagnostic) = diagnostics.get(&FrameTimeDiagnosticsPlugin::FPS) {
@@ -244,12 +267,44 @@ fn change_text_system(
  }
  }
 
- text.sections[0].value = format!(
- "This text changes in the bottom right - {fps:.1} fps, {frame_time:.3} ms/frame",
+ text.sections[0].value =
+ format!("{avg_fps:.1} avg fps, {fps_variance:.1} frametime variance",);
+
+ text.sections[1].value = format!(
+ "\nThis text changes in the bottom right - {fps:.1} fps, {frame_time:.3} ms/frame",
  );
 
- text.sections[3].value = format!("{fps:.1}");
+ text.sections[4].value = format!("{fps:.1}");
 
- text.sections[5].value = format!("{frame_time:.3}");
+ text.sections[6].value = format!("{frame_time:.3}");
+ }
+}
+
+fn mean(data: &[f64]) -> Option<f64> {
+ let sum = data.iter().sum::<f64>();
+ let count = data.len();
+
+ match count {
+ positive if positive > 0 => Some(sum / count as f64),
+ _ => None,
+ }
+}
+
+fn std_deviation(data: &[f64]) -> Option<f64> {
+ match (mean(data), data.len()) {
+ (Some(data_mean), count) if count > 0 => {
+ let variance = data
+ .iter()
+ .map(|value| {
+ let diff = data_mean - *value;
+
+ diff * diff
+ })
+ .sum::<f64>()
+ / count as f64;
+
+ Some(variance.sqrt())
+ }
+ _ => None,
  }
 }