This module is a fork of TheNickmaster21's repository which is a fork of Defaultio's repository. I forked this repository to update the typescript package to BehaviorTrees5.
BehaviorTree5(Latest update: May 5th, 2022)
V5: (May 2022)
- Added Metaprox's External Task fork, to allow for rojo support
- Fixed critical issue in behavior trees where multiple actors wouldn't properly keep track of their running states
BehaviorTree5 is an implementation of the "behavior tree" paradigm for managing behavior. This allows us to create relatively complex patterns of behavior without much getting "lost in the sauce", so to speak. In behavior trees, actions are represented as tasks, or "leaves". These tasks are then collected in a container called a tree, which we "run" through in order to determine what task should be done at a given point in time.
Nodes
Nodes contain information about how to handle something. This can either be a task, or a manipulation of tasks. In BT2, there are 3 types of nodes:
- Leafs
- Composites
- Decorators
The read me for BehaviorTree3 can be found here: https://github.com/Defaultio/BehaviorTree3/blob/master/README.md
Leafs
Leafs are the foundation of BT3. They define how to act.
Tasks
The most commonly used leaf is a Task. Let's take a look at how they're written.
local SUCCESS,FAIL,RUNNING = 1,2,3
local NewNode = BehaviorTree5.Task({
-- 'start' and 'finish' functions are optional. only "run" is required!
start = function(object, ...)
object.i = 0
print("I've prepped the task!")
end,
run = function(object, ...)
object.i = object.i+1
if object.i == 5 then
return SUCCESS
elseif object.i > 5 then
return FAIL
end
print("The task is still running...")
return RUNNING
end,
finish = function(object, status, ...)
object.i = nil
print("I'm done with the task! My outcome was: ")
if status == SUCCESS then
print("Success!")
elseif status == FAIL then
print("Fail!")
end
end
})
Tasks are created by calling BehaviorTree5.Task(), with a table defining different task functions. When we run a behavior tree, it will "process" a node in the order start -> run -> finish. These functions will always be called in this order.
The start and finish functions are usually used to prep and cleanup the work that a task does, like initializing and destroying object properties. However, it is not necessary to define them. A task will function perfectly fine with just the run function alone.
The run function is the "base of operations" for a task. Here, we handle anything we would want to do. When we "run" a behavior tree, we would do so in steps. If we wanted real-time behavior, for example, we could run our trees within RunService.Heartbeat. Keep in mind the rate at which you will be processing trees when defining this function. Think about where to change the task state of a node when writing your function as well. Consider when it should fail so that you don't create unintended behavior. (i.e. attacking when you should be walking instead) Remember that you can only call one state per step.
Notice the object, ... parameters passed to start, run, and finish. This object is a table that is passed to the tree when run is called on it, and any additional parameters are also passed along.
Blackboard Query
When running a tree on an object, a Blackboard table will be injected into the object if one does not exist already. This can be used by the Blackboard Query node for easy state lookup. A blackboard query is commonly used to see if a value is set or not in order to dictate the flow of relevant logic in a tree.
You can achieve the same effect with tasks, but it's a bit faster if you only need to perform a simple boolean or nil check
Trees
The Tree is a special Leaf type that will execute another tree and pass the result of that tree to its parent.
local AnotherTree = BehaviorTree5:new(...)
local NewNode = BehaviorTree5.Task({tree = AnotherTree})
Composites
These nodes take multiple Leafs and give them order. In BT3, we have Sequence, Selector, Random types for Compites.
Sequence
The Sequence process the nodes it is given in sequence of the order they are defined. If any of its subnodes fail, then it will not continue to process the subnodes that follow it and return a fail state itself.
Sequence = BehaviorTree5.Sequence({
nodes = {
node1,
node2, -- if this failed, the next step would process node1
node3
}
})
Selector
The Selector node will process every node until one of them succeeds, after which it will return success itself. If none of its subnodes succeed, then this Composite would return a fail state.
Priority = BehaviorTree5.Selector({
nodes = {
node1,
node2,
node3 -- this is the only node that suceeded, so Priority would return success
}
})
Random
This Selector will randomly select a subnode to process, and will return whatever state that node returns.
Random = BehaviorTree5.Random({
nodes = {
node1,
node2,
node3
}
})
Nodes can also have an optional weight attribute that will affect Random. Default is 1.
local SUCCESS,FAIL,RUNNING = 1,2,3
node1 = BehaviorTree5.Task({
weight = 10,
run = function(object)
print("Weight: 10")
return SUCCESS
end
})
node2 = BehaviorTree5.Task({
weight = 10,
run = function(object)
print("Also weight: 10")
return SUCCESS
end
})
node3 = BehaviorTree5.Task({
weight = 200,
run = function(object)
print('You probably won't see "Weight: 10" printed'.)
return SUCCESS
end
})
While
The While Only accepts two children, a condition(1st child), and an action(2nd child) It repeats until either the condition returns fail, wherein the node itself returns fail, or the action returns success, wherein the node itself returns success.
While = BehaviorTree5.While({
nodes = {
condition, -- If this node returns fail, return fail
action -- When this node returns success, return success
}
})
Decorators
Decorators are nodes that wrap other nodes and alter their task state. Right now, there are Succeed, Fail, Invert, and Repeat decorators. Succeed, Fail, and Invert are pretty self-explanatory, and are helpful for when you start making more complex trees via nested Collections.
These can be written as such.
Invert = BehaviorTree5.Invert({
nodes = {nodeHere}
})
Repeat decorators will repeat their children node tasks until count, or indefinitely if count is nil or < 0, after which they will return a success state. If breakonfail is true and its child node fails, it will stop repeating and return a fail state.
Repeat = BehaviorTree5.Repeat({
nodes = {nodeHere},
count = 3,
breakonfail = true
})
The Tree
Once you have your nodes set up and ready to go, we can start planting some trees. A Tree usually starts with any Selector, which should have Task nodes in them or other Selector nodes with other nodes in them. They can be instantiated by calling BehaviorTree5:new() with a table containing tree information as its only argument.
Tree = BehaviorTree5:new({
tree = BehaviorTree5.Sequence({
nodes = {
node1,
node2,
BehaviorTree5.Random({
nodes = {
node3,
node4
}
})
}
})
})
As you can see, we can nest Composite nodes within each other. This is where the magic of behavior trees come in!
Running trees
To run a tree, call :run on the tree object, passing it a table. This table is the relevant object or actor that tree is dictating behavior for. You can also pass any additional parameters you desire, and these will be passed along to the task functions.
local actorObject = {...}
Tree = BehaviorTree5:new({
tree = BehaviorTree5.Sequence({
-- nodes from earlier
})
})
while true do
local treeStatus = Tree:run(actorObject)
wait(1)
end
That's pretty much all there is to BehaviorTree5. Go nuts with it or something. If you have any issues or questions, feel free to ask about them on the devforum post: https://devforum.roblox.com/t/btreesv5-rojo-support-fixes/