Gio's StateMachines

Overview

A framework for implementing general purpose StateMachines in Unreal Engine, leveraging the blueprint graph and UObjects.

• Supports UE4 and UE5
• Blueprint friendly
• Flexible and extensible

GioStateMachines was built with two main goals:

1. Enabling the blueprint graph to define transitions between different states in a state machine, leveraging the visual aspect of blueprints, and also allowing designers to build functional state machines from a set of predefined state classes.
2. Encouraging abstraction between different states in the state machine, to avoid filling the state machine's logic with dependencies.

Here's how it works:

GioNode

The core class for all states and state machines. A Node is a simple UObject which can be Entered, Exited and Ticked*. It has inputs and outputs, which represent points that it can be entered from, and exited to. The purpose of these points is to allow abstraction between different nodes in the state machine. Inputs and Outputs can be defined in the class default panels, or set via code during construction.

*The Tick is not automatic, and must be manually called. If you don't want to manually call it, use the StateMachineRunnerComponent

Nodes can also Return. This tells their owning state machine to return to the previous Node, if applicable.

A Node also contains a pointer to a StateMachineData object. This is set by the owning state machine before entering the Node. By default, the StateMachineData instance is shared across the state machine, and is meant to serve as a way to transfer data between different Nodes. This behaviour can be overriden.

There are a few useful custom blueprint nodes that these states respond to:

• Node Entered: Exposes one execution pin for each input in the Node class.
• Exit Node: Exposes one execution pin for each output in the Node class. Will request exit via the pin that gets executed.

GioStateMachine

The state machine is a Node which contains child nodes (states). There will only be one node active at a time, and it will be Ticked along with the state machine. A state machine can also run another state machine, since they inherit the GioNode base class. The state machine also has a property to define what class its StateMachineData should be. By default, whenever the state machine is entered, a new instance of the state machine data class will be created. This instance will be passed on to any child nodes, enabling them to share data. This behaviour can be overriden.

This class is meant to be blueprinted to define transitions between Nodes using the blueprint graph. Along with the basic blueprint nodes available to GioNode, the state machine can also use a special node:

• Enter Node: Tells the state machine to enter a new state. The state is defined by class, and a new instance of it will be created the first time the node is accessed. One execution pin will be created for each input and output available for that node class.

State machines can have various applications, such as a CharacterStateMachine to handle all different states of the player's characters, or a MainMenuStateMachine to handle all different screens in the main menu of the game. You could even make a GameStateMachine that encapsulates each different part of the application flow as an individual node.

GioStateMachineData

Simple UObject that is meant to transfer data between different nodes in a state machine. You should sub-class this and define your own set of variables and events this object should hold. By default, a new instance of it will be created when a state machine is entered, and the instance will be shared with all its child nodes. This enables two separate nodes in the state machine to communicate, with a level of abstraction between them.

To do

• Persistence
• StateEnter node
• RequestExit node
• Double-click targets
• StateMachineComponent
• StateMachineData
• Protected name validation (PN_Exec, PN_Then)
• State history and Return
• Nested StateMachines
• When UClass updates, refresh nodes
• Examples
  • Dialogue
  • UI Flow
  • Actor states