From 3227c3de368ea3a82e14c28a058b7c979bd35bf4 Mon Sep 17 00:00:00 2001
From: UkoeHB <37489173+UkoeHB@users.noreply.github.com>
Date: Mon, 2 Sep 2024 12:01:59 -0500
Subject: [PATCH] Don't reallocate scale factors in measure_text_system
 (#14999)

# Objective

- Reuse allocation of `scale_factors` in `measure_text_system`.

## Solution

- Move it to a `Local`.
---
 crates/bevy_ui/src/widget/text.rs | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/crates/bevy_ui/src/widget/text.rs b/crates/bevy_ui/src/widget/text.rs
index 3cb0dbfbe3979..515dae7f05bf6 100644
--- a/crates/bevy_ui/src/widget/text.rs
+++ b/crates/bevy_ui/src/widget/text.rs
@@ -152,7 +152,9 @@ fn create_text_measure(
 ///     is only able to detect that a `Text` component has changed and will regenerate the `Measure` on
 ///     color changes. This can be expensive, particularly for large blocks of text, and the [`bypass_change_detection`](bevy_ecs::change_detection::DetectChangesMut::bypass_change_detection)
 ///     method should be called when only changing the `Text`'s colors.
+#[allow(clippy::too_many_arguments)]
 pub fn measure_text_system(
+    mut scale_factors_buffer: Local<EntityHashMap<f32>>,
     mut last_scale_factors: Local<EntityHashMap<f32>>,
     fonts: Res<Assets<Font>>,
     camera_query: Query<(Entity, &Camera)>,
@@ -171,14 +173,14 @@ pub fn measure_text_system(
     >,
     mut text_pipeline: ResMut<TextPipeline>,
 ) {
-    let mut scale_factors: EntityHashMap<f32> = EntityHashMap::default();
+    scale_factors_buffer.clear();
 
     for (entity, text, content_size, text_flags, camera, mut buffer) in &mut text_query {
         let Some(camera_entity) = camera.map(TargetCamera::entity).or(default_ui_camera.get())
         else {
             continue;
         };
-        let scale_factor = match scale_factors.entry(camera_entity) {
+        let scale_factor = match scale_factors_buffer.entry(camera_entity) {
             Entry::Occupied(entry) => *entry.get(),
             Entry::Vacant(entry) => *entry.insert(
                 camera_query
@@ -208,7 +210,7 @@ pub fn measure_text_system(
             );
         }
     }
-    *last_scale_factors = scale_factors;
+    std::mem::swap(&mut *last_scale_factors, &mut *scale_factors_buffer);
 }
 
 #[allow(clippy::too_many_arguments)]
@@ -284,6 +286,7 @@ fn queue_text(
 #[allow(clippy::too_many_arguments)]
 pub fn text_system(
     mut textures: ResMut<Assets<Image>>,
+    mut scale_factors_buffer: Local<EntityHashMap<f32>>,
     mut last_scale_factors: Local<EntityHashMap<f32>>,
     fonts: Res<Assets<Font>>,
     camera_query: Query<(Entity, &Camera)>,
@@ -301,14 +304,14 @@ pub fn text_system(
         &mut CosmicBuffer,
     )>,
 ) {
-    let mut scale_factors: EntityHashMap<f32> = EntityHashMap::default();
+    scale_factors_buffer.clear();
 
     for (node, text, text_layout_info, text_flags, camera, mut buffer) in &mut text_query {
         let Some(camera_entity) = camera.map(TargetCamera::entity).or(default_ui_camera.get())
         else {
             continue;
         };
-        let scale_factor = match scale_factors.entry(camera_entity) {
+        let scale_factor = match scale_factors_buffer.entry(camera_entity) {
             Entry::Occupied(entry) => *entry.get(),
             Entry::Vacant(entry) => *entry.insert(
                 camera_query
@@ -341,5 +344,5 @@ pub fn text_system(
             );
         }
     }
-    *last_scale_factors = scale_factors;
+    std::mem::swap(&mut *last_scale_factors, &mut *scale_factors_buffer);
 }