BTSequence does not return SUCCESS when the last action is successful until the after first action has run again in some cases.

[nickswebsite]

BTSequence does not return a SUCCESSful status when the last action is successful. Currently it waits for the next tick to reset itself and report success.

While this doesn't appear to be a problem for trivial cases, when a child node of an FSMStateIntegratedBT that is configured to fire an event on success, the event does not get fired until the first task of the sequence has already run. This is particularly problematic if the first task is intended to check conditions based on the current state of the game world.

The 'minimal' scene setup:

• Node2D
  • FiniteStateMachine
  • FSMStateIntegratedBT # Fires an finished event on success.
    • BTRoot
    • BTSequence
      • ActionA # set a value on the black board and return SUCCESS
      • ActionB # do something for a tick (returning RUNNING) then return SUCCESS on the next tick.
    • FSMTransition # transitions to FSMState below on finished
  • FSMState # Starts a timer _on_enter()
    • FSMTransition # Transitions back to FSMStateIntegratedBT on timeout

Ultimately what will happen is this:

• ActionA runs
• ActionB runs
• ActionA runs
• FSMState is entered

I would have expected this sequence:

• ActionA
• ActionB
• FSMState is entered
• ActionA

The offending lines of code appear to be in bt_sequence.gd:

func tick(delta: float, actor: Node, blackboard: Blackboard):
    if current_leaf > leaves.size() -1:
        current_leaf = 0
        return BTStatus.SUCCESS

    var response = leaves[current_leaf].tick(delta, actor, blackboard)

    if response == BTStatus.RUNNING:
        return response

    if response == BTStatus.FAILURE:
        current_leaf = 0
        return response

    current_leaf += 1
    return BTStatus.RUNNING

I can put in a PR for a fix, but I really don't have any good way to know if doing so would introduce issues elsewhere. When I see a slightly awkward construction like this, I have to think there is a reason for it.

[nickswebsite]

After digging a little deeper, it appears that the BTRoot and the FiniteStateMachine nodes are fighting each other during the _process_code(). BTRoot._process_code() runs after FiniteStateMachine._process_code(), so BTRoot.current_status doesn't get updated (and no event is fired) during the frame.

I had to make sure SUCCESS was returned from BTSequence when the last action was completed successfully, AND alter FSMStateIntegratedBT in the following manner:

• Disable the BTRoot by setting BTRoot.process_mode = Node.PROCESS_MODE_DISABLED from _ready()
• Manually invoking behaviour_tree._process_code(_delta) during its _on_update() method.

[nickswebsite]

I added an example scene here: https://github.com/ThePat02/BehaviourToolkit/pull/83