What problem does this solve or what need does it fill?

Being able to run arbitrary code at a defined point in time on an animation is sometimes really useful.

Example use case

• spawn particles/sound effects every time a characters feet hits the ground in a walk animation.
• a character is attacking, deal damage to nearby enemies after a delay.

What solution would you like?

I'd like a way to define "triggers" in an animations that executes a command or similar (event?), rather than animating some property.

something like:

#[derive(Event, Clone)]
enum Say {
    Hello,
    Bye,
}

fn say(trigger: Trigger<Say>) {
    match trigger.event() {
        Say::Hello => println!("Helloo!"),
        Say::Bye => println!("Bye!"),
    }
}

animation.trigger(1.0, Say::Hello); // can be any event type
animation.trigger(2.0, Say::Bye);

or maybe:

animation.add_triggers([1.0, 2.0], ["hello", "bye"]);

What alternative(s) have you considered?

You can get pretty far using Timers but it would take some effort to have it synced with an animation.

Additional context

Also seen in other engines such as unreal engine, unity and godot.