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FSM (Finite State Machine)

A fair chunk of the game's logic (quests, moves & ai behavior) is scripted using FSMs - Finite State Machines.

You can find a fair chunk of these files in system/fsm files. They will always have the _fsm_ingame suffix - for some reason it is required.

Tip

You can preview FSMs using RelinkToolkit2.

Layers

Sometimes FSMs are made up of smaller graphs called layers. When the FSM reaches the end of a layer, execution will go back to the beginning of it, not the start of the FSM. For FSM execution to fully complete, nodes that transition to other nodes usually have a transition with FSMUnderLayerEndCondition, which waits for the layer to be complete.

File Structure

The FSMs file built in a depth-first manner. The game will iterate over every node in the file, link them to conditions and execution components accordingly, and then, build the final tree with the root node.

  • The game iterates through all nodes.
  • FSMNode declares a new node on the graph. They may point to other nodes with conditions.
    • When childLayerId_ is set, that means this node points to a new layer. The first node of that layer is always the root of that layer.
    • tailIndexOfChildNodeGuids_ is practically the number of nodes in this layer. This is only set for root (and layer root) nodes.
  • layerNo_ sets the current layer the nodes belong to. Note that layers may be completely empty (leftover metadata) and not necessarily used.
  • Transition links a node to another using fromNodeGuid_ and toNodeGuid_. Note that they are in reverse - Cygames mistake. toNodeGuid_ is the SOURCE node while fromNodeGuid_ is the TARGET node.
    • conditionGuids_ links to condition components, aka the specified conditions to check on for this transition to occur while params_ are how the conditions are linked, i.e OR or AND, and their priority/order of execution. (there should always be one param between two conditions. So 3 conditions = 2 params.)
    • isEndTransition_ refers to FSM end. It doesn't necessarily point to a node that actually exists in the file, which, doesn't matter.
    • NOTE: Purpose of transitions/branches that do not have toNodeGuid_ is currently unclear. RelinkToolkit2 shows these as green arrows.
  • addAllTransition - TODO
  • addTransition - TODO
  • EnableBaseTransition - TODO
  • EnableBaseAllTransition - TODO
  • Anything else is an execution or condition, name is an fsm object engine reflected based on its name which internally inherits from BehaviorTreeComponent. A list can be found here.
    • For conditions (which must inherit from ConditionComponent internally), isReverseSuccess_ means whether if a condition fails, then it is considered a success. This is equivalent to if (!success).
    • For actions, these will be linked up to nodes using parentGuid_.
  • Then, the tree is built - all nodes will have children linked to. This starts from the first node in the graph, and then recursively to the bottom.