Observer Run Conditions - Bevy

Run conditions are a convenient, reusable pattern for skipping systems when certain conditions are met. Previously, run conditions only worked for ordinary systems. Observers couldn't use them.

Now, they can!

rust

#[derive(Resource)]
struct GamePaused(bool);

// Observer only runs when game is not paused
app.add_observer(
    on_damage.run_if(|paused: Res<GamePaused>| !paused.0)
);

// Multiple conditions can be chained (AND semantics)
app.add_observer(
    on_damage
        .run_if(|paused: Res<GamePaused>| !paused.0)
        .run_if(resource_exists::<Player>)
);

This works with add_observer, entity .observe(), and the Observer builder pattern.