The Power of Finite State Machines: Concept and Creation

This two-part tutorial will cover creating a multi-state car using a finite state machine. We will start with Procedural FSM and progress into the State Pattern design pattern. Concept and creation will be our main focus during this first part; we will then proceed into application and extension during the second part.

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Final Result Preview

Let’s take a look at the final result we will be working towards:

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What Is a Finite State Machine?

Wikipedia defines an FSM (Finite State Machine) as a mathematical abstraction sometimes used to design digital logic or computer programs. It is a behavior model composed of a finite number of states, transitions between those states, and actions, similar to a flow graph in which one can inspect the way logic runs when certain conditions are met.

It has finite internal memory; an input feature that reads symbols in a sequence, one at a time, without going backward; and an output feature, which may be in the form of a user interface, once the model is implemented. The operation of an FSM begins from one of the states (called a start state), goes through transitions (depending on the inputs) to different states, and can end in any of those available – however, only a certain set of states mark a successful flow of operation.

In my own words, an FSM is a device used by developers to create objects that have different behaviors determined by the current state they are in. Depending on the input, the object can react and/or transition to a different state.

One good example would be a 1970 HK VP70Z machine pistol, which has three firing modes: safety, single shot, and semi-automatic three-round burst. Depending on the current mode you have it set to (state), the result (output) is different when you pull the trigger (input).

Tools: When conceptualizing an idea (the multi-state object you’re trying to create), it’s best to use a State Transition Table to know what states and actions for those states you will need to add.

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Step 1: Setup

It’s time to start a new project. With FlashDevelop, create a new AS3 project. For the name, put CarFSM. Click “Browse…” and save it to your desired location. Go into the Package slot and enter “com.activeTuts.fsm”. Make sure the “Create directory for project” checkbox is selected then click “OK” to finish.

Read more: The Power of Finite State Machines: Concept and Creation