UnityLearn - Beginner Programming - Finite State Machine - Pt. 01 - Managing State

Novemeber 15, 2019

Beginner Programming: Unity Game Dev Courses

Beginner Programming: Unity Game Dev Courses
Unity Learn Course - Beginner Programming

Managing State

Project Overview

This part of the tutorial has a lot more hands on parts, so I skip some of the sections for note purposes when there is not much substance to them other than following inputs.

The basics covered in this section are:
What is state and how to manage it
Finite State Machine pattern
Build your own finite state machine

Introduction

State: condition of something variable
State Examples: Game state, Player state, NPC State

Finite State Machine: abstract machine that can be in exactly one of a finite number of states at any given time

Parts of a Finite State Machine:
  • List of possible states
  • Conditions for transitioning between those states
  • State its in when initialized (initial state)

Naive Approach to Managing State

This naive approach focuses on boolean states and if staements. It uses a lot of if and else if statements in the Update method to determine what state the player is in and if/when/how they can switch to another state. Even with two states this becomes tedious and somewhat difficult to read. This example is just to emphasize the use of proper finite state machines.

Actions, Triggers, & Conditions

Look at your actions as a set of: actions, triggers, conditions.
Example for Arthur jumping:

  • Actions: Arthur jumps; jumping expression
  • Triggers: Spacebar is pressed
  • Conditions: Arthur is not jumping

Continuing to follow the naive state management approach, we see that everytime we add a new state it makes all snippets about other states more complex and harder to follow. This is very clear that this will become unmanagealbe with only a few states even.

Module Overview

The biggest issue with the naive approach is the interdependent logic of the various states. It makes each state exponentially harder to work with with every state that is added, so it is very limited on its scalability. This does not even come with a benefit to readability, as it also becomes difficult to read quickly.

SUMMARY

Using the naive approach (boolean fields and if/else statements) to manage state is only really useable for extremely simple cases. As soon as you reach 3 or 4 states with even small amounts of logic to manage them, this approach becomes very awkward and unwieldy. Fininte State Machines should hopefully open up a better way to manage more states with better scalability and allow for more complexity with better readability.

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