Description

I wanted to just use a state machine purely in GDscript, as simply as possible, but with states, transitions, hooks, and conditions/triggers to change states

• States: the FSM will always be in a state. It will change to another state with the transitions, following the first transaction, having the current state as a source, that matches the conditions/trigger
• Transition: a transition will allow the FSM to change from one state to another when, at each update
  • The transition is fully matched the (optional) trigger has been called
  • The (optional) conditions has all been met
  • A transition is composed of
    • A state source
    • A state destination
    • An optional list of conditions
    • An optional trigger
• Transition source: in order to reduce the amount of code to type for transitions, there are some helpers. source can be a string (STATE), or it can be an array:
  • STATE: any known state (the easy one)
  • "*": all the states (including the destination)
  • ^STATE: all the states but STATE. e.g. "^hurt" => it will match, for source, all the states except "hurt"
  • -STATE: remove STATE from the previous states added (when source is an array). e.g. ["*", "-idle", "-hurt"] => it will match, for source, all the states except "idle" and "hurt"
• Trigger: a transition can be mapped to 0 or 1 trigger. A trigger is emitted by calling the "trigger" method, and the trigger will be treated at the next update and then forgotten
• Condition: a condition is just the callback of a method returning a boolean. It can be the name of the method, or it can prefixed by "!" to get the reverse boolean

TODO

• Maybe optimize the whole thing

How to use

• Add it to your project : https://docs.godotengine.org/en/stable/tutorials/plugins/editor/installing_plugins.html#enabling-a-plugin

    mkdir -p addons
    cd addons
    git submodule add ssh://git@git.abxy.fr:212/groug/godot_simple_state_machine.git

• Add the custom StateMachine node (name it "StateMachine" for the purpose of the example)
• Initialize the states, initial state and conditions:

	$StateMachine.add_state("idle")
	$StateMachine.add_state("hurt")
	$StateMachine.add_state("dead")
	$StateMachine.set_init_state("idle")
	$StateMachine.add_transition("idle", "hurt", [], "fire")
	$StateMachine.add_transition("hurt", "dead", ["has_stuff_been_handled", "is_dead"])
	$StateMachine.add_transition("hurt", "idle", ["has_stuff_been_handled"])

• Trigger an event

	$StateMachine.trigger("fire")

• Add a condition: it's just a func returning a bool

    def has_stuff_been_handled():
        return true

• Add callbacks for state entering/update/exiting: just add the state name in on_XXXXX_state_YYYY()

    func on_idle_state_enter():
        pass

    func on_idle_state_update(delta):
        pass

    func on_idle_state_exit():
        pass

• Enabling debug mode (logs when changing states)

    $StateMachine.set_debug_enabled(true)

• Get the current state

    $StateMachine.get_current_state()

• Get the last known state (before the current one)

    $StateMachine.get_last_state()

Credits

icon: made by Freepik from https://www.flaticon.com, license: Creative Commons BY 3.0