86 lines
4.7 KiB
Markdown
86 lines
4.7 KiB
Markdown
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# Hivemind
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Hivemind is a [Behavior Tree](http://en.wikipedia.org/wiki/Behavior_Trees_(Artificial_Intelligence,_Robotics_and_Control)) implementation for Unity3D that features a visual editor with runtime visual debugging capabilities.
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## Warning!
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This project is in early development, and while everything described bellow is currently functional, keep in mind:
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- Many node types are simply not yet implemented (a warning will be displayed in the inspector for these) and will always return the Error status.
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- There might be many undiscovered bugs.
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- Performance will probably degrade rapidly with very large trees or many concurrent agents.
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## What is a Behavior Tree?
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Behavior Trees are widely used in the game development industry (as well as other fields such as robotics) that allows a designer to map a complex set of branching actions, sensors and conditions that simulate inteligent behavior in an artificial agent, be it an individual game character or a virtual oponent or ally controlling multiple agents or game mechanics.
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## How to use Hivemind to implement Behavior Trees in your game
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### The Behavior Tree asset
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A Hivemind `Behavior Tree` is a reusable custom assets that you store in your Unity project, and behave similarly to the native `Animator Controller`.
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As any other asset, simply chose `Assets / Create / Behavior Tree` to create a Hivemind Behavior Tree asset in your project.
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With a Behavior Tree asset selected in your Project view, you can bring up the visual editor by clicking `Window / Behavior Tree Editor`.
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A newly created Behavior Tree will have a single "root" node. Most of the visual editor functionality is controlled via right-click context menus on the nodes and the editor background, as well as the Unity3D inspector for configuring selected nodes.
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### The Behavior Tree Agent component
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`Behavior Tree Agent` is a component that can be added to any `GameObject`, that lets you assign an existing Behavior Tree to that Game Object to create AI enabled agents in your game.
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### Action Libraries
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Actions are mapped to methods in classes that inherit from `Hivemind.ActionLibrary`. The action library methods can then be decorated with the `[Hivemind.Action]` attribute, making that action available in the visual editor.
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##### Variables
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Action Libraries have two inherited variables:
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- `agent`: holds a reference to the current agent
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- `context`: a dictionary-like structure that can be used to pass data between actions, instantiated once per behavior tree, per agent
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##### Implementing Action Libraries
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Actions can be as generic as the designer wants them, so that they can be reused as much as possible in the project.
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An action library class is instantiated (on demand) once per agent, per behavior tree. The behavior tree will call the `Start` function of the action library as soon as the library is instantiated and the agent and context variables have been populated, so the user can do any necessary initialization.
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Multiple Action Libraries can be used in a Behavior Tree, but each will only be instantiated once.
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Actions __must__ return a value from the `Hivemind.Status` enum, which include:
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- `Success`
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- `Failure`
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- `Running`
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- `Error`
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##### Parameters
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The method parameters can be used to configure an action node. Currently, only the C# primitives `string` and `float` are allowed. More C# primitives and other value types, as well as common Unity3D object references are planned for future implementation.
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##### Context
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The current Context, accessible via the `context` variable inherited from `Hivemind.ActionLibrary`, is a key-value store similar to dictionaries, but implemented as a C# generic. It has the following public methods:
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- `Set<T>(string key, T value)`: Sets a value of type T
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- `Get<T>(string key)`: Retrieves a value of type T
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- `Unset(string key)`: Removes a value from the context
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Action methods can be decorated with attributes that hint to Context values that method expects or populates, and these will show up on the visual editor inspector:
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- `[Hivemind.Expects(string key, Type type)]`
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- `[Hivemind.Outputs(string key, Tyoe type)]`
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In the future, a design-time debugging feature will ensure context values required by an action are populated in previous actions. For the moment, a designer can use the above attributes as reference.
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### Debugging
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To watch the execution of a behavior tree in real time, make sure you have selected a _Game Object_ that has a _Behavior Tree Agent_ component attached, and open the _Behavior Tree Editor window_. The screenshot above illustrates a runing Behavior Tree.
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Additionaly, the current _Context_ is displayed in the _Behavior Tree Agent_ component inspector. |