Demo the UI with a dummy machine

This finally shows the basic operating principle of the machine UIs.
There will be some object out in the world that, when clicked, will open
a new UI screen to operate the machine.

Next up is to attach various bits of info, like a `Fuel` component on
the machine which the UI widget locates and displays as text. This gives
me the infrastructure necessary to begin that work.

src/main.rs

@@ -1,7 +1,10 @@
-use bevy::{prelude::*, window::WindowResolution};
+use bevy::{color::palettes::css::GREEN, prelude::*, window::WindowResolution};
 use bevy_inspector_egui::{bevy_egui::EguiPlugin, quick::WorldInspectorPlugin};
 
-use crate::game::machines::{CuttingMachine, RotatingMachine};
+use crate::{
+  game::machines::{CuttingMachine, RotatingMachine},
+  resources::UiTheme,
+};
 
 mod assets;
 mod card;
@@ -21,15 +24,7 @@ fn main() {
     .add_plugins(EguiPlugin::default())
     .add_plugins(WorldInspectorPlugin::new())
     .add_plugins(widgets::GameUiPlugin)
-    .add_systems(
-      Startup,
-      (
-        setup,
-        assets::load_assets,
-        RotatingMachine::spawn_ui,
-        CuttingMachine::spawn_ui,
-      ),
-    )
+    .add_systems(Startup, (setup, assets::load_assets, dummy_machine))
     .run();
 }
 
@@ -43,3 +38,27 @@ fn despawn<T: Component>(mut commands: Commands, to_despawn: Query<Entity, With<
     commands.entity(entity).despawn();
   }
 }
+
+fn dummy_machine(
+  mut commands: Commands,
+  // mut meshes: ResMut<Assets<Mesh>>,
+  // mut materials: ResMut<Assets<ColorMaterial>>,
+) {
+  commands
+    .spawn((
+      Sprite::from_color(GREEN, Vec2::splat(40.0)),
+      // WARN: Mesh picking is not part of the `DefaultPlugins` plugin collection!
+      // (but sprite picking is!)
+
+      // Mesh2d(meshes.add(Rectangle::new(25., 25.))),
+      // MeshMaterial2d(materials.add(ColorMaterial::from_color(GREEN))),
+      Transform::default(),
+      Pickable::default(),
+    ))
+    .observe(
+      |event: Trigger<Pointer<Click>>, commands: Commands, theme: Res<UiTheme>| {
+        let entity = event.target;
+        CuttingMachine::spawn_ui(commands, theme);
+      },
+    );
+}