Add tests and document text2d aabb creation

Author: Kanabenki

crates/bevy_text/Cargo.toml

@@ -33,5 +33,8 @@ glyph_brush_layout = "0.2.1"
 thiserror = "1.0"
 serde = { version = "1", features = ["derive"] }
 
+[dev-dependencies]
+approx = "0.5.1"
+
 [lints]
 workspace = true

crates/bevy_text/src/text2d.rs

@@ -246,11 +246,133 @@ pub fn calculate_bounds_text2d(
     >,
 ) {
     for (entity, layout_info, anchor) in &text_to_update_aabb {
+        // `Anchor::as_vec` gives us an offset relative to the text2d bounds, by negating it and scaling
+        // by the logical size we compensate the transform offset in local space to get the center.
+        let center = (-anchor.as_vec() * layout_info.logical_size)
+            .extend(0.0)
+            .into();
+        // Distance in local space from the center to the x and y limits of the text2d bounds.
+        let half_extents = (layout_info.logical_size / 2.0).extend(0.0).into();
         commands.entity(entity).try_insert(Aabb {
-            center: (-anchor.as_vec() * layout_info.logical_size)
-                .extend(0.0)
-                .into(),
-            half_extents: (layout_info.logical_size / 2.0).extend(0.0).into(),
+            center,
+            half_extents,
         });
     }
 }
+
+#[cfg(test)]
+mod tests {
+
+    use bevy_app::{App, Update};
+    use bevy_asset::{load_internal_binary_asset, Handle};
+    use bevy_ecs::{event::Events, schedule::IntoSystemConfigs};
+    use bevy_utils::default;
+
+    use super::*;
+
+    const FIRST_TEXT: &str = "Sample text.";
+    const SECOND_TEXT: &str = "Another, longer sample text.";
+
+    fn setup() -> (App, Entity) {
+        let mut app = App::new();
+        app.init_resource::<Assets<Font>>()
+            .init_resource::<Assets<Image>>()
+            .init_resource::<Assets<TextureAtlasLayout>>()
+            .init_resource::<TextSettings>()
+            .init_resource::<FontAtlasWarning>()
+            .init_resource::<FontAtlasSets>()
+            .init_resource::<Events<WindowScaleFactorChanged>>()
+            .insert_resource(TextPipeline::default())
+            .add_systems(
+                Update,
+                (
+                    update_text2d_layout,
+                    calculate_bounds_text2d.after(update_text2d_layout),
+                ),
+            );
+
+        // A font is needed to ensure the text is layed out with an actual size.
+        load_internal_binary_asset!(
+            app,
+            Handle::default(),
+            "FiraMono-subset.ttf",
+            |bytes: &[u8], _path: String| { Font::try_from_bytes(bytes.to_vec()).unwrap() }
+        );
+
+        let entity = app
+            .world
+            .spawn((Text2dBundle {
+                text: Text::from_section(FIRST_TEXT, default()),
+                ..default()
+            },))
+            .id();
+
+        (app, entity)
+    }
+
+    #[test]
+    fn calculate_bounds_text2d_create_aabb() {
+        let (mut app, entity) = setup();
+
+        assert!(!app
+            .world
+            .get_entity(entity)
+            .expect("Could not find entity")
+            .contains::<Aabb>());
+
+        // Creates the AABB after text layouting.
+        app.update();
+
+        let aabb = app
+            .world
+            .get_entity(entity)
+            .expect("Could not find entity")
+            .get::<Aabb>()
+            .expect("Text should have an AABB");
+
+        // Text2D AABB does not have a depth.
+        assert_eq!(aabb.center.z, 0.0);
+        assert_eq!(aabb.half_extents.z, 0.0);
+
+        // AABB has an actual size.
+        assert!(aabb.half_extents.x > 0.0 && aabb.half_extents.y > 0.0);
+    }
+
+    #[test]
+    fn calculate_bounds_text2d_update_aabb() {
+        let (mut app, entity) = setup();
+
+        // Creates the initial AABB after text layouting.
+        app.update();
+
+        let first_aabb = *app
+            .world
+            .get_entity(entity)
+            .expect("Could not find entity")
+            .get::<Aabb>()
+            .expect("Could not find initial AABB");
+
+        let mut entity_ref = app
+            .world
+            .get_entity_mut(entity)
+            .expect("Could not find entity");
+        *entity_ref
+            .get_mut::<Text>()
+            .expect("Missing Text on entity") = Text::from_section(SECOND_TEXT, default());
+
+        // Recomputes the AABB.
+        app.update();
+
+        let second_aabb = *app
+            .world
+            .get_entity(entity)
+            .expect("Could not find entity")
+            .get::<Aabb>()
+            .expect("Could not find second AABB");
+
+        // Check that the height is the same, but the width is greater.
+        approx::assert_abs_diff_eq!(first_aabb.half_extents.y, second_aabb.half_extents.y);
+        assert!(FIRST_TEXT.len() < SECOND_TEXT.len());
+        assert!(first_aabb.half_extents.x < second_aabb.half_extents.x);
+    }
+}