SODA and Finite State Machines

Hello All, I hope everyone is at least as well as the last time I posted on here, hopefully even better. I wanted to write here today to update on my current projects. I am happy to announce that Liquidators, a yearlong project I have been lucky enough to be the lead producer of, has released a playable and open demo, for free. I would love to have support from my site and receive feedback on this game! It is a survival horror game based on the real life events which followed the reactor meltdown at Chernobyl. The demo can be downloaded HERE.

I will of course keep my site in the loop about this game, as we plan for a steam release this summer, hopefully. However, this is a site dedicated to my personal code and projects so I will carry on to stuff that you will definitely find less interesting than a nuclear reactor survival horror game which is literally free right up there ^. You could play it for FREE but you’re still reading this? Fine, if you’ve made it this far lets talk about scriptable objects and how I’ve been using them in my Finite State Machines in a separate, yet still cool, side project.

A little about this “side” project:

Been in production for almost 3 weeks

I’m working as the only engineer, Game being built in Unity, Being built for gamepad controllers (using primitive input system (I know))

it’s a 2 player endless runner

Player 1(Dog) can choose when to throw player 2(Boomerang)

Boomerang player aims themselves before throw

Dog player only has control of left and right movement, constantly moving forward

Boomerang player can control left, right, and forward back, still constantly moving forward, just at adjusted rate

Players try to survive as long as possible

Each have abilities they can use to help each other

“Tokens” used when using ability

Cylinder is enemy only boomeang can kill, kills dog. Wall blockades kill both

Here’s a clip:

So here, you could imagine there are a few player states. Specifically, a state for each player when the boomerang is with the dog, for when the dog and boomerang are separate, and for when the boomerang dies and the dog persists. A Finite State Machine helps us out here because none of these states will be coexisting. So, each player will have their own instance of a StateMachine, which takes an iState, and they must communicate with one another, to ensure they are in proper states at all times, since one of their states being out of sync would inherently break the other’s state (since their controls are dependent upon one another).

If you have read my other posts here , or here, or here, or here or- okay you get it.. If you’ve seen those posts or the title of this one, you know that I love SODA. So given our state machine above, SODA fits into this very well. The first issue presented above is that our state machines must know the state of one another. SODA Events really help us with this here. When the dog throws the boomerang, it’s an event. The dog script doesn’t even communicate with the boomerang script directly. It simply invokes that event, and the GameEventListener on the Boomerang is quick to respond, switching to its “free” state, after a throwing thread, of course. This exists for all my state transitions here, except for the boomerang being caught by the Dog for that requires a synchronous tap of a button by both players. But you can see how that would ensure our State machine stay in our intended state.

The next BIG help from SODA in these FSMs is that my IntVariable type, the Scriptable Object int I’ve made, can be passed into my states, where they have free access to the value they need, and receive all live updates to that number via that reference. Confused? Imagine this: My dog player location is stored in my Vector3Variable Scriptable Object. In my state constructor, I take a type Vector3Variable _playerLocation. Now _playerLocation.value will be a reference to the exact spot in memory where my Player Location value is stored. Whether I just want to access it, or even adjust it, that value is live, and feeding into any other script that may need that live number. This is huge because normally I would have to make a reference to my player in every script that needs that number, and store it again in that script. Furthermore, by taking it in the state constructor, I don’t have to pester my player script to retrieve it every frame, because in the case of a value that is changed elsewhere, my state script will receive that update instantly through the magic of SODA!

I hope this makes sense, but in case it doesn’t, here’s some code:

//This is a state for player 1's movement, while the boomerang is in its backpack
//Here you have my declaration of the Variables I will need in this State
//Protecting these variables calmed down an empty value warning I was gettig
    protected Vector3Variable _dogLocation;
//Player speed can be changed at any time
    protected FloatVariable _playerSpeed;

//Player can move, or not
    protected BoolVariable _playerCanMove;

//Reference to Dog script
    protected DogPlayerMovement _player;

public ISDogRunning (Vector3Variable dogLocation, FloatVariable playerSpeed, BoolVariable playerCanMove, DogPlayerMovement player)
//Simply taking the references I have, and setting equal to the Variable I need
        _dogLocation = dogLocation;
        _playerSpeed = playerSpeed;
        _playerCanMove = playerCanMove;
        _player = player;


//This is my state Tick, run every frame
public void OnStateTick ()
        if (_playerCanMove.value)
            //Moves player forwards
            _player.transform.Translate (Vector3.forward * Time.deltaTime * _playerSpeed);

            //Allows player to move LR
            _player.transform.Translate (Vector3.right * Time.deltaTime * Input.GetAxis ("P1Left Stick Horizontal") * horizontalMovementMod);

            //Throw boomerang when A pressed
            //Keyboard controls for debug
            if (Input.GetButtonDown ("P1A Button") || Input.GetKeyDown (KeyCode.E))
                //Tells player to throw
                _player.BoomerangThrown (aimLocation);

            //Reads for player using ability
            if (Input.GetButtonDown ("P1B Button") || Input.GetKeyDown (KeyCode.R))
                _player.UseSelectedDogAbility ();

            //Allows player to switch through abilities
            if (Input.GetButtonDown ("P1X Button") || Input.GetKeyDown (KeyCode.F))
                _player.SwitchDogAbility ();

        //Gets player's aim
        //This state actually reads input from player 2 as well, as aiming component was initially part of dog
        //Axis is between -1 and 1, adding 1 and then dividing by 2 to get complete input
        aimLocation = Vector3.Lerp (_player.GetLeftAimLimit (), _player.GetRightAimLimit (), ((Input.GetAxis ("P2Left Stick Horizontal")) + 1) / 2);

        //Will rotate arrow assigned to plauer
        arrowGO.transform.LookAt (aimLocation);

        //Puts aim point at aim locations
        aimPointGO.transform.position = aimLocation;

        //Updates player's location
        _dogLocation.value = _player.transform.position;

3 thoughts on “SODA and Finite State Machines

  1. Liquidators is such a cool concept! Post-Chernobyl would have to be a perfect setting for a horror game to take place. That being said, I can’t play horror games myself (lest I get a heart attack) so unfortunately, I’ll have to sit out on the demo. 😨 Your side project looks like a lot of fun though. SODA sounds like it can save a ton of memory and shrink a game file size down significantly!


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