feat: add feature to create session lock surfaces.

- Allow users to create session lock surfaces by passing an event
`SessionLockEvent::Lock` and unlock them using
`SessionLockEvent::Unlock`.
- Other surfaces of the application should be destroyed before the
session lock is aquired. The wayland client is only allowed to render to
the lock surfaces while the lock is active.

examples/session_lock.rs

@@ -0,0 +1,212 @@
+use std::time::Duration;
+
+use bevy::{
+    color::palettes::basic::*,
+    prelude::*,
+    window::{exit_on_all_closed, WindowCreated, WindowRef, WindowResolution},
+    winit::WinitPlugin,
+};
+use bevy_wayland::{
+    layer_shell::LayerShellSettings,
+    session_lock::{SessionLockEvent, SessionLockWindow},
+    WaylandPlugin,
+};
+use smithay_client_toolkit::shell::wlr_layer::{Anchor, Layer};
+
+const NORMAL_BUTTON: Color = Color::srgb(0.15, 0.15, 0.15);
+const HOVERED_BUTTON: Color = Color::srgb(0.25, 0.25, 0.25);
+
+fn main() {
+    App::new()
+        .add_plugins((
+            DefaultPlugins
+                .build()
+                .disable::<WinitPlugin>()
+                .set(WindowPlugin {
+                    primary_window: None,
+                    ..Default::default()
+                }),
+            WaylandPlugin,
+        ))
+        .add_systems(Startup, setup)
+        .add_systems(
+            Update,
+            (
+                button_system,
+                exit_on_esc,
+                setup_session_lock_windows,
+                exit_on_all_closed,
+            ),
+        )
+        .run();
+}
+
+#[allow(clippy::type_complexity)]
+fn button_system(
+    mut interaction_query: Query<
+        (
+            &Interaction,
+            &mut BackgroundColor,
+            &mut BorderColor,
+            &Children,
+        ),
+        (Changed<Interaction>, With<UnlockButton>),
+    >,
+    mut text_query: Query<&mut Text>,
+    mut session_lock_event_writer: EventWriter<SessionLockEvent>,
+) {
+    for (interaction, mut color, mut border_color, children) in &mut interaction_query {
+        let mut text = text_query.get_mut(children[0]).unwrap();
+        match *interaction {
+            Interaction::Pressed => {
+                session_lock_event_writer.write(SessionLockEvent::Unlock);
+            }
+            Interaction::Hovered => {
+                **text = "Click to unlock".to_string();
+                *color = HOVERED_BUTTON.into();
+                border_color.0 = Color::WHITE;
+            }
+            Interaction::None => {
+                **text = "Click to unlock".to_string();
+                *color = NORMAL_BUTTON.into();
+                border_color.0 = Color::BLACK;
+            }
+        }
+    }
+}
+
+#[derive(Component)]
+struct LockButton;
+#[derive(Component)]
+struct UnlockButton;
+
+fn setup(
+    mut commands: Commands,
+    assets: Res<AssetServer>,
+    windows: Query<Entity, With<Window>>,
+
+    mut session_lock_event_writer: EventWriter<SessionLockEvent>,
+) {
+    session_lock_event_writer.write(SessionLockEvent::Lock);
+    for entity in &windows {
+        commands.entity(entity).insert((LayerShellSettings {
+            anchor: Anchor::TOP | Anchor::LEFT,
+            layer: Layer::Bottom,
+            ..Default::default()
+        },));
+    }
+    // ui camera
+    commands.spawn(Camera2d);
+    commands.spawn(lock_button(&assets));
+}
+
+#[derive(Component)]
+struct ConfiguredWindow;
+#[derive(Component)]
+struct SessionLockCamera;
+
+fn setup_session_lock_windows(
+    mut commands: Commands,
+    asset_server: Res<AssetServer>,
+    windows: Query<(Entity, &SessionLockWindow), Without<ConfiguredWindow>>,
+) {
+    for (entity, _) in &windows {
+        let camera = commands
+            .spawn((
+                Camera2d,
+                Camera {
+                    target: bevy::render::camera::RenderTarget::Window(WindowRef::Entity(entity)),
+                    ..Default::default()
+                },
+                SessionLockCamera,
+            ))
+            .id();
+        commands.entity(entity).insert(ConfiguredWindow);
+        commands.spawn(unlock_button(&asset_server, camera));
+    }
+}
+
+fn exit_on_esc(keys: Res<ButtonInput<KeyCode>>) {
+    if keys.just_pressed(KeyCode::Escape) {
+        std::process::exit(0);
+    }
+}
+
+fn lock_button(asset_server: &AssetServer) -> impl Bundle + use<> {
+    (
+        Node {
+            width: Val::Percent(100.0),
+            height: Val::Percent(100.0),
+            align_items: AlignItems::Center,
+            justify_content: JustifyContent::Center,
+            ..default()
+        },
+        children![(
+            Button,
+            LockButton,
+            Node {
+                width: Val::Px(250.0),
+                height: Val::Px(65.0),
+                border: UiRect::all(Val::Px(5.0)),
+                // horizontally center child text
+                justify_content: JustifyContent::Center,
+                // vertically center child text
+                align_items: AlignItems::Center,
+                ..default()
+            },
+            BorderColor(Color::BLACK),
+            BorderRadius::MAX,
+            BackgroundColor(NORMAL_BUTTON),
+            children![(
+                Text::new("Button"),
+                TextFont {
+                    font: asset_server.load("fonts/FiraSans-Bold.ttf"),
+                    font_size: 33.0,
+                    ..default()
+                },
+                TextColor(Color::srgb(0.9, 0.9, 0.9)),
+                TextShadow::default(),
+            )]
+        )],
+    )
+}
+
+fn unlock_button(asset_server: &AssetServer, camera: Entity) -> impl Bundle + use<> {
+    (
+        Node {
+            width: Val::Percent(100.0),
+            height: Val::Percent(100.0),
+            align_items: AlignItems::Center,
+            justify_content: JustifyContent::Center,
+            ..default()
+        },
+        UiTargetCamera(camera),
+        children![(
+            Button,
+            UnlockButton,
+            Node {
+                width: Val::Px(250.0),
+                height: Val::Px(65.0),
+                border: UiRect::all(Val::Px(5.0)),
+                // horizontally center child text
+                justify_content: JustifyContent::Center,
+                // vertically center child text
+                align_items: AlignItems::Center,
+                ..default()
+            },
+            BorderColor(Color::BLACK),
+            BorderRadius::MAX,
+            BackgroundColor(NORMAL_BUTTON),
+            children![(
+                Text::new("Button"),
+                TextFont {
+                    font: asset_server.load("fonts/FiraSans-Bold.ttf"),
+                    font_size: 33.0,
+                    ..default()
+                },
+                TextColor(Color::srgb(0.9, 0.9, 0.9)),
+                TextShadow::default(),
+            )]
+        )],
+    )
+}