From 37fefd855e90ef6c08928c98b3a1980d53b6162c Mon Sep 17 00:00:00 2001
From: Oliver Nordbjerg <hi@notbjerg.me>
Date: Fri, 11 Jul 2025 16:14:12 +0200
Subject: [PATCH] Add `max_history_length` to `EntityCountDiagnosticsPlugin`

---
 .../src/entity_count_diagnostics_plugin.rs    | 23 ++++++++++++++++---
 examples/diagnostics/log_diagnostics.rs       |  2 +-
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/crates/bevy_diagnostic/src/entity_count_diagnostics_plugin.rs b/crates/bevy_diagnostic/src/entity_count_diagnostics_plugin.rs
index b20a82bf6c..8a1754a43d 100644
--- a/crates/bevy_diagnostic/src/entity_count_diagnostics_plugin.rs
+++ b/crates/bevy_diagnostic/src/entity_count_diagnostics_plugin.rs
@@ -1,15 +1,32 @@
 use bevy_app::prelude::*;
 use bevy_ecs::entity::Entities;
 
-use crate::{Diagnostic, DiagnosticPath, Diagnostics, RegisterDiagnostic};
+use crate::{
+    Diagnostic, DiagnosticPath, Diagnostics, RegisterDiagnostic, DEFAULT_MAX_HISTORY_LENGTH,
+};
 
 /// Adds "entity count" diagnostic to an App.
 ///
 /// # See also
 ///
 /// [`LogDiagnosticsPlugin`](crate::LogDiagnosticsPlugin) to output diagnostics to the console.
-#[derive(Default)]
-pub struct EntityCountDiagnosticsPlugin;
+pub struct EntityCountDiagnosticsPlugin {
+    /// The total number of values to keep.
+    pub max_history_length: usize,
+}
+
+impl Default for EntityCountDiagnosticsPlugin {
+    fn default() -> Self {
+        Self::new(DEFAULT_MAX_HISTORY_LENGTH)
+    }
+}
+
+impl EntityCountDiagnosticsPlugin {
+    /// Creates a new `EntityCountDiagnosticsPlugin` with the specified `max_history_length`.
+    pub fn new(max_history_length: usize) -> Self {
+        Self { max_history_length }
+    }
+}
 
 impl Plugin for EntityCountDiagnosticsPlugin {
     fn build(&self, app: &mut App) {
diff --git a/examples/diagnostics/log_diagnostics.rs b/examples/diagnostics/log_diagnostics.rs
index 0e00e69ccd..1a36f9a1f2 100644
--- a/examples/diagnostics/log_diagnostics.rs
+++ b/examples/diagnostics/log_diagnostics.rs
@@ -33,7 +33,7 @@ fn main() {
             // Adds frame time, FPS and frame count diagnostics.
             FrameTimeDiagnosticsPlugin::default(),
             // Adds an entity count diagnostic.
-            EntityCountDiagnosticsPlugin,
+            EntityCountDiagnosticsPlugin::default(),
             // Adds cpu and memory usage diagnostics for systems and the entire game process.
             SystemInformationDiagnosticsPlugin,
             // Forwards various diagnostics from the render app to the main app.