Godot C# State Machine

Simple, easy to use lightweight state machine for Godot or other games using C#. There are no state machine parent class; states are all maintained as individual instances which can be changed at each update cycle.

Usage

1. In the object you want to turn into a state machine, create a field called currentState or something similar:

using StateMachine;

public class StateMachineLike 
{
  State currentState;
  ...
}

2. Initialize all the required states in the constructor using the State's public constructors or State.Builder.

State idle = State.Builder
    .Create("Idle") // Pass a string to name the state. Useful for storing sprite/animation names
    .OnPerform(delta => {
      // Action on idle
    })
    .OnEntry(() => {
      // Action when the state started
    })
    .Build();

3. Initialize all transitions using the contructor or Transition.Builder.

4. Connect states using State.SetTransitions()

5. Set currentState to the initial state

6. In the Update function, do:

currentState = currentState.PerformAndTransition(delta); 
// Delta is the time since last frame; it's only used in each state's own Action functions. 
// Set it to some random number if you don't need it.

Perform and Transition simplies perform the Action of the current state, and check all of its transition for their respective conditions. It then returns a new state if a condition has been met, or the same state.

7. Voilà! You've got yourself a state machine that performs an action on each Update frame, and can transition based on conditions in each transition object.

Idea

State

States are basically wrapper for an Action function, with string data for Name and Sprite, and two optional actions for Entry and Exit. They hold a list of transitions, which are ways of connecting states to other states.

Transitions

Transitions are just a wrapper for a Func that takes a state as a param and returns a bool. They also hold a single state object which represents the state to transition to. If you imagine a state machine like a graph, a transition is the line connecting to another state, just with an extra connection to the destination state.