Behave-Graph
Behave-Graph is a standalone library that implements the concept of "behavior graphs" as a portable TypeScript library with no external run-time dependencies. Behavior graphs are expressive, deterministic, and extensible state machines that can encode arbitrarily complex behavior.
Behavior graphs are used extensively in game development as a visual scripting language. For example, look at Unreal Engine Blueprints or Unity's Visual Scripting or NVIDIA Omniverse's OmniGraph behavior graphs.
This library is intended to follow industry best practices in terms of behavior graphs. It is also designed to be compatible with these existing implementations in terms of capabilities. Although, like all node-based systems, behavior graphs are always limited by their node implementations.
Another neat fact about behavior graphs is that they offer a sand boxed execution model. Because one can only execute what is defined by nodes exposed by the host system, you can restrict what can be executed by these graphs. This type of sand-boxing is not possible when you just load and execute arbitrary scripts.
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Feature Overview
This library, while small, contains a nearly complete implementation of behavior graphs.
Features:
- Customizable While this library contains a lot of nodes, you do not have to expose all of them. For example, just because this supports for-loops and state, does not mean you have to register that node type as being available.
- Type Safe This library is implemented in TypeScript and fully makes use of its type safety features.
- Small This is a very small library with no external dependencies.
- Simple This library is implemented in a forward fashion without unnecessary complexity.
Node Types:
- Events You can implement arbitrary events that start execution: Start, Tick
- Actions You can implement actions that trigger animations, scene scene variations, or update internal state: Log
- Logic You can do arithmetic, trigonometry as well as vector operations and string manipulation: Add, Subtract, Multiply, Divide, Pow, Exp, Log, Log2, Log10, Min, Max, Round, Ceil, Floor, Sign, Abs, Trunc, Sqrt, Negate, And, Or, Not, ==, >, >=, <, <=, isNan, isInfinity, concat, includes.
- Queries You can query the state from the system.
- Flow Control Control execution flow using familiar structures: Branches, delays, if-then, sequences and for-loops.
- State You can set and load state arbitrarily: Exists, Set, Get.
- Time Time nodes allow you to wait: Delay.
Designed for Integration into Other Systems
This library is designed to be extended with context dependent nodes, specifically Actions, Events and Queries that match the capabilities and requirements of your system. For example, if you integrate into a 3D engine, you can query for player state or 3D positions of your scene graph, set scene graph properties and also react to overlaps, and player movements. Or if you want to integrate into an AR system, you can react to face-detected, tracking-loss.
Command Line Usage
Building
After cloning out this git project locally, run the following:
npm install
npm run buildExamples
The example behavior graphs are in the /examples folder. You can execute these from the command line to test out how this library works.
The main syntax is this one:
npm run exec-graph -- ./examples/[examplename].jsonHere are some example graphs in their native JSON form:
Hello World
Print out the text "Hello World!" as soon as the graph starts up!
[
{
"type": "event/start"
},
{
"type": "action/log",
"inputs": {
"flow": { "links": [ { "node": 0, "socket": "flow" } ] },
"text": { "value": "Hello World!" }
}
}
]Console output:
> npm run exec-graph -- ./examples/basics/HelloWorld.json
Hello World!Setting and Reading State
In this example, we set a state variable called "counter" to 1000 and then later read it and print it out.
[
{
"type": "event/start"
},
{
"type": "state/setNumber",
"inputs": {
"flow": { "links": [ { "node": 0, "socket": "flow" } ] },
"identifier": { "value": "counter"},
"value": { "value": 1000 }
}
},
{
"type": "state/getNumber",
"inputs": {
"identifier": { "value": "counter" }
}
},
{
"type": "logic/numberToString",
"inputs": {
"a": { "links": [ { "node": 2, "socket": "result" } ] }
}
},
{
"type": "action/log",
"inputs": {
"flow": { "links": [ { "node": 1, "socket": "flow" } ] },
"text": { "links": [ { "node": 3, "socket": "result" } ] }
}
}
]Console output:
> npm run exec-graph -- ./examples/basics/State.json
1000Branching
This example shows how to branching execution works. The "flow/branch" node has two flow outputs, "true" and "false". The value of it's "condition" input determines the path of execution.
[
{
"type": "event/start"
},
{
"type": "flow/branch",
"inputs": {
"flow": { "links": [ { "node": 0, "socket": "flow" } ] },
"condition": { "value": false }
}
},
{
"type": "action/log",
"inputs": {
"flow": { "links": [ { "node": 1, "socket": "true" } ] },
"text": { "value": "Condition is true!" }
}
},
{
"type": "action/log",
"inputs": {
"flow": { "links": [ { "node": 1, "socket": "false" } ] },
"text": { "value": "Condition is false!" }
}
}
]Console output:
> npm run exec-graph -- ./examples/basics/Branch.json
Condition is false!Polynomial Math Formula
This shows how to create math formulas in logic nodes. In this case the equation is: ( a^1 * 3 + a^2 + (-a^3) ), where a = 3. The answer is -9.
[
{
"type": "event/start"
},
{
"type": "logic/numberConstant",
"inputs": {
"a": { "value": 3 }
}
},
{
"type": "logic/numberPow",
"inputs": {
"a": { "links": [ { "node": 1, "socket": "result" } ] },
"b": { "value": 1 }
}
},
{
"type": "logic/numberPow",
"inputs": {
"a": { "links": [ { "node": 1, "socket": "result" } ] },
"b": { "value": 2 }
}
},
{
"type": "logic/numberPow",
"inputs": {
"a": { "links": [ { "node": 1, "socket": "result" } ] },
"b": { "value": 3 }
}
},
{
"type": "logic/numberMultiply",
"inputs": {
"a": { "links": [ { "node": 2, "socket": "result" } ] },
"b": { "value": 3 }
}
},
{
"type": "logic/numberAdd",
"inputs": {
"a": { "links": [ { "node": 5, "socket": "result" } ] },
"b": { "links": [ { "node": 3, "socket": "result" } ] }
}
},
{
"type": "logic/numberNegate",
"inputs": {
"a": { "links": [ { "node": 4, "socket": "result" } ] },
"b": { "value": 10 }
}
},
{
"type": "logic/numberAdd",
"inputs": {
"a": { "links": [ { "node": 6, "socket": "result" } ] },
"b": { "links": [ { "node": 7, "socket": "result" } ] }
}
},
{
"type": "logic/numberToString",
"inputs": {
"a": { "links": [ { "node": 8, "socket": "result" } ] }
}
},
{
"type": "action/log",
"inputs": {
"flow": { "links": [ { "node": 0, "socket": "flow" } ] },
"text": { "links": [ { "node": 9, "socket": "result" } ]}
}
}
]Console output:
> npm run exec-graph -- ./examples/basics/Math.json
-9Asynchronous Execution
Behave-Graph support asynchronous nodes. These are nodes which will continue execution non-immediately but on their own self-determined schedule. This allows for things such as "Delay" nodes that can sleep for a period of time.
[
{
"type": "event/start"
},
{
"type": "action/log",
"inputs": {
"flow": { "links": [ { "node": 0, "socket": "flow" } ] },
"text": { "value": "Waiting..." }
}
},
{
"type": "time/delay",
"inputs": {
"flow": { "links": [ { "node": 1, "socket": "flow" } ] },
"duration": { "value": 1 }
}
},
{
"type": "action/log",
"inputs": {
"flow": { "links": [ { "node": 2, "socket": "flow" } ] },
"text": { "value": "One Second Later!" }
}
}
]Console output:
> npm run exec-graph -- ./examples/basics/Delay.json
Waiting...
One Second Later!