FontSmoothing fixes (#22455)

# Objective

1. The `font_smoothing` field of `TextFont` is ignored in main
currently. Instead it always uses `FontSmoothing::Antialiased`.
2. The `FontSmoothing` enum is missing from the `bevy_text` prelude.
3. The `FontSmoothing` bug wasn't caught by the screenshot CI.

## Solution

1. Store the antialiasing mode in `ComputedTextBlock`, for use in
`TextPipeline::update_buffer`.
2. Add `FontSmoothing` to `bevy_text::prelude`.
3. Add a font smoothing example to `testbed_ui`'s `Text` scene.

## Testing

Check `testbed_ui`'s text scene.

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>

Author: ickshonpe

crates/bevy_text/src/pipeline.rs

@@ -176,8 +176,12 @@ impl TextPipeline {
             for (span_index, (entity, depth, span, text_font, _color, line_height)) in
                 text_spans.enumerate()
             {
-                // Save this section entity in the computed text block.
-                computed.entities.push(TextEntity { entity, depth });
+                // Save this span entity in the computed text block.
+                computed.entities.push(TextEntity {
+                    entity,
+                    depth,
+                    font_smoothing: text_font.font_smoothing,
+                });
 
                 if span.is_empty() {
                     continue;
@@ -371,8 +375,7 @@ impl TextPipeline {
 
                 let mut temp_glyph;
                 let span_index = layout_glyph.metadata;
-                let font_smoothing = FontSmoothing::AntiAliased;
-
+                let font_smoothing = computed.entities[span_index].font_smoothing;
                 let layout_glyph = if font_smoothing == FontSmoothing::None {
                     // If font smoothing is disabled, round the glyph positions and sizes,
                     // effectively discarding all subpixel layout.

crates/bevy_text/src/text.rs

@@ -33,6 +33,8 @@ pub struct TextEntity {
     pub entity: Entity,
     /// Records the hierarchy depth of the entity within a `TextLayout`.
     pub depth: usize,
+    /// Antialiasing method to use when rendering the text.
+    pub font_smoothing: FontSmoothing,
 }
 
 /// Computed information for a text block.

examples/testbed/ui.rs

@@ -149,7 +149,7 @@ mod image {
 }
 
 mod text {
-    use bevy::{color::palettes::css::*, prelude::*};
+    use bevy::{color::palettes::css::*, prelude::*, text::FontSmoothing};
 
     pub fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
         commands.spawn((Camera2d, DespawnOnExit(super::Scene::Text)));
@@ -607,6 +607,25 @@ mod text {
                 ),
             ],
         ));
+
+        for font_smoothing in [FontSmoothing::AntiAliased, FontSmoothing::None] {
+            top += 35.;
+            commands.spawn((
+                Node {
+                    left: px(100.),
+                    top: px(top),
+                    ..Default::default()
+                },
+                Text::new(format!("FontSmoothing::{:?}", font_smoothing)),
+                TextFont {
+                    font: asset_server.load("fonts/MonaSans-VariableFont.ttf").into(),
+                    font_size: 25.,
+                    font_smoothing,
+                    ..default()
+                },
+                DespawnOnExit(super::Scene::Text),
+            ));
+        }
     }
 }