Introduce testbed examples starting with 2d (#15954)

# Objective

- Make progress for #15918 
- Start with 2d

## Solution

- Remove screenshots for existing examples as they're not deterministic
- Create new "testbed" example category, with a 2d one to start

## Testing

- Run `CI_TESTING_CONFIG=.github/example-run/testbed_2d.ron cargo run
--example testbed_2d --features "bevy_ci_testing"`
- ???
- Check the screenshots

.github/example-run/breakout.ron

@@ -3,7 +3,6 @@
         fixed_frame_time: Some(0.03),
     ),
     events: [
-        (200, Screenshot),
         (900, AppExit),
     ]
 )

.github/example-run/load_gltf.ron

@@ -3,7 +3,6 @@
         frame_time: Some(0.03),
     ),
     events: [
-        (100, Screenshot),
         (300, AppExit),
     ]
 )

.github/example-run/testbed_2d.ron

@@ -0,0 +1,12 @@
+(
+    events: [
+        (100, Screenshot),
+        (200, Custom("switch_scene")),
+        (300, Screenshot),
+        (400, Custom("switch_scene")),
+        (500, Screenshot),
+        (600, Custom("switch_scene")),
+        (700, Screenshot),
+        (800, AppExit),
+    ]
+)

.github/workflows/send-screenshots-to-pixeleagle.yml

@@ -19,7 +19,7 @@ on:
 jobs:
   send-to-pixel-eagle:
     name: Send screenshots to Pixel Eagle
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-24.04
     steps:
       
       - name: Download artifact

Cargo.toml

@@ -3834,3 +3834,12 @@ name = "Monitor info"
 description = "Displays information about available monitors (displays)."
 category = "Window"
 wasm = false
+
+# Testbed
+[[example]]
+name = "testbed_2d"
+path = "examples/testbed/2d.rs"
+doc-scrape-examples = true
+
+[package.metadata.example.testbed_2d]
+hidden = true

examples/testbed/2d.rs

@@ -0,0 +1,172 @@
+//! 2d testbed
+//!
+//! You can switch scene by pressing the spacebar
+
+#[cfg(feature = "bevy_ci_testing")]
+use bevy::dev_tools::ci_testing::CiTestingCustomEvent;
+use bevy::prelude::*;
+
+fn main() {
+    let mut app = App::new();
+    app.add_plugins((DefaultPlugins,))
+        .init_state::<Scene>()
+        .enable_state_scoped_entities::<Scene>()
+        .add_systems(OnEnter(Scene::Shapes), shapes::setup)
+        .add_systems(OnEnter(Scene::Bloom), bloom::setup)
+        .add_systems(OnEnter(Scene::Text), text::setup)
+        .add_systems(OnEnter(Scene::Sprite), sprite::setup)
+        .add_systems(Update, switch_scene);
+    app.run();
+}
+
+#[derive(Debug, Clone, Eq, PartialEq, Hash, States, Default)]
+enum Scene {
+    #[default]
+    Shapes,
+    Bloom,
+    Text,
+    Sprite,
+}
+
+fn switch_scene(
+    keyboard: Res<ButtonInput<KeyCode>>,
+    #[cfg(feature = "bevy_ci_testing")] mut ci_events: EventReader<CiTestingCustomEvent>,
+    scene: Res<State<Scene>>,
+    mut next_scene: ResMut<NextState<Scene>>,
+) {
+    let mut should_switch = false;
+    should_switch |= keyboard.just_pressed(KeyCode::Space);
+    #[cfg(feature = "bevy_ci_testing")]
+    {
+        should_switch |= ci_events.read().any(|event| match event {
+            CiTestingCustomEvent(event) => event == "switch_scene",
+        });
+    }
+    if should_switch {
+        info!("Switching scene");
+        next_scene.set(match scene.get() {
+            Scene::Shapes => Scene::Bloom,
+            Scene::Bloom => Scene::Text,
+            Scene::Text => Scene::Sprite,
+            Scene::Sprite => Scene::Shapes,
+        });
+    }
+}
+
+mod shapes {
+    use bevy::prelude::*;
+
+    const X_EXTENT: f32 = 900.;
+
+    pub fn setup(
+        mut commands: Commands,
+        mut meshes: ResMut<Assets<Mesh>>,
+        mut materials: ResMut<Assets<ColorMaterial>>,
+    ) {
+        commands.spawn((Camera2d, StateScoped(super::Scene::Shapes)));
+
+        let shapes = [
+            meshes.add(Circle::new(50.0)),
+            meshes.add(CircularSector::new(50.0, 1.0)),
+            meshes.add(CircularSegment::new(50.0, 1.25)),
+            meshes.add(Ellipse::new(25.0, 50.0)),
+            meshes.add(Annulus::new(25.0, 50.0)),
+            meshes.add(Capsule2d::new(25.0, 50.0)),
+            meshes.add(Rhombus::new(75.0, 100.0)),
+            meshes.add(Rectangle::new(50.0, 100.0)),
+            meshes.add(RegularPolygon::new(50.0, 6)),
+            meshes.add(Triangle2d::new(
+                Vec2::Y * 50.0,
+                Vec2::new(-50.0, -50.0),
+                Vec2::new(50.0, -50.0),
+            )),
+        ];
+        let num_shapes = shapes.len();
+
+        for (i, shape) in shapes.into_iter().enumerate() {
+            // Distribute colors evenly across the rainbow.
+            let color = Color::hsl(360. * i as f32 / num_shapes as f32, 0.95, 0.7);
+
+            commands.spawn((
+                Mesh2d(shape),
+                MeshMaterial2d(materials.add(color)),
+                Transform::from_xyz(
+                    // Distribute shapes from -X_EXTENT/2 to +X_EXTENT/2.
+                    -X_EXTENT / 2. + i as f32 / (num_shapes - 1) as f32 * X_EXTENT,
+                    0.0,
+                    0.0,
+                ),
+                StateScoped(super::Scene::Shapes),
+            ));
+        }
+    }
+}
+
+mod bloom {
+    use bevy::{
+        core_pipeline::{bloom::Bloom, tonemapping::Tonemapping},
+        prelude::*,
+    };
+
+    pub fn setup(
+        mut commands: Commands,
+        mut meshes: ResMut<Assets<Mesh>>,
+        mut materials: ResMut<Assets<ColorMaterial>>,
+    ) {
+        commands.spawn((
+            Camera2d,
+            Camera {
+                hdr: true,
+                ..default()
+            },
+            Tonemapping::TonyMcMapface,
+            Bloom::default(),
+            StateScoped(super::Scene::Bloom),
+        ));
+
+        commands.spawn((
+            Mesh2d(meshes.add(Circle::new(100.))),
+            MeshMaterial2d(materials.add(Color::srgb(7.5, 0.0, 7.5))),
+            Transform::from_translation(Vec3::new(-200., 0., 0.)),
+            StateScoped(super::Scene::Bloom),
+        ));
+
+        commands.spawn((
+            Mesh2d(meshes.add(RegularPolygon::new(100., 6))),
+            MeshMaterial2d(materials.add(Color::srgb(6.25, 9.4, 9.1))),
+            Transform::from_translation(Vec3::new(200., 0., 0.)),
+            StateScoped(super::Scene::Bloom),
+        ));
+    }
+}
+
+mod text {
+    use bevy::prelude::*;
+
+    pub fn setup(mut commands: Commands) {
+        let text_font = TextFont {
+            font_size: 50.0,
+            ..default()
+        };
+        let text_justification = JustifyText::Center;
+        commands.spawn((Camera2d, StateScoped(super::Scene::Text)));
+        commands.spawn((
+            Text2d::new("Hello World"),
+            text_font,
+            TextLayout::new_with_justify(text_justification),
+            StateScoped(super::Scene::Text),
+        ));
+    }
+}
+
+mod sprite {
+    use bevy::prelude::*;
+
+    pub fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
+        commands.spawn((Camera2d, StateScoped(super::Scene::Sprite)));
+        commands.spawn((
+            Sprite::from_image(asset_server.load("branding/bevy_bird_dark.png")),
+            StateScoped(super::Scene::Sprite),
+        ));
+    }
+}