Title menu background: an endless battle at a bridge over an underground river

- dungeon creatures against knights, balanced reinforcements for the weaker side
- towers on both banks; heavy units go for them, destroyed towers are rebuilt after 25 s
- the camera slowly circles the bridge; battle sounds stay muted; the demo is never saved

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/main.rs

@@ -3,6 +3,7 @@
 mod audio;
 mod campaign;
 mod cloud;
+mod demo;
 mod dwarves;
 mod fortress;
 mod game;
@@ -374,7 +375,8 @@ async fn main() {
     menu.has_autosave = platform::storage_get(save::AUTOSAVE_KEY).is_some();
 
     let seed = (miniquad::date::now() * 1000.0) as u32 | 1;
-    let (game, cam) = new_game(seed, &settings);
+    // behind the title menu: the endless bridge battle
+    let (game, cam) = Game::new_demo(seed);
     let mut app = App { game, cam, settings, seed, status: None, recorded: false };
     menu.progress = platform::storage_get(PROGRESS_KEY).and_then(|s| serde_json::from_str(&s).ok()).unwrap_or_default();
     app.game.hints = app.settings.hints;
@@ -814,6 +816,8 @@ async fn main() {
                             menu.has_autosave = true;
                         }
                         menu.page = Some(Page::Title);
+                        app.seed = next_seed(app.seed);
+                        (app.game, app.cam) = Game::new_demo(app.seed);
                     }
                     MenuAction::None | MenuAction::Consumed => {}
                 }
@@ -948,7 +952,13 @@ async fn main() {
             app.game.hints = app.settings.hints;
         }
 
-        // ---------------- update (the world stands still while menus or dialogs are open)
+        // ---------------- update (the world stands still while menus or dialogs are open;
+        // the bridge battle behind the title menu goes on, the camera slowly circles it)
+        if app.game.demo.is_some() && !playing {
+            app.game.update(dt);
+            app.cam.yaw += dt * 0.03;
+            app.game.events.retain(|ev| ev.pos.is_none());
+        }
         if playing {
             for _ in 0..(app.settings.game_speed.round().max(1.0) as usize) {
                 app.game.update(dt);