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

@@ -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);
 }