00:04Hi everyone and welcome to a series that many of you have requested me to cover which is state trees
00:07Now state trees were introduced in Unreal 5
00:10Uh I can't remember which point it was but one of them and it keeps getting updated with new exciting new features and I'm pretty happy where it is right now
00:18So decided to do a video series about it explaining how it works and why you want to use it over say behavior trees um and various things like that
00:27Now, let's go through the b some of the basics first before we start showing examples of how to actually use one
00:34And let's jump in
00:37So, the very first thing you need to do is enable the plugin for them
00:40So, go to your plugins and just search for state tree
00:45We're in Unreal 5.5.4
00:48So, it may it wasn't turned on by default in this one
00:50It may change for future versions, but all you have to do is make sure you got gameplay state tree turned on
00:56And this is state tree
00:56State tree for AI/gameplay behaviors
00:58Now this is important to note is difference between state tree and behaviors is a behavior tree is exclusively really for AI
01:08But this can be used for things that are not AI
01:11You can do it for doors, you can do it for chests, you can do it for targets, you can do it all sorts of things, not just AI
01:16So it's really quite more flexible
01:18So turn it on
01:20It'll ask you to restart
01:20Restart it and you're good to go
01:24Okay
01:24Okay
01:24So to create a new state tree, all you have to do is go into your browser, go to AI artificial intelligence, and go to state tree
01:33You're given two extra uh components here
01:36So state tree component is the state tree for all the generic actor actors
01:41So let's say you want to do one for a door, that would make sense to do one for that
01:45If you want to do one for an AI actor, so like a character running around for example, you get the state tree AI component
01:51Now, this one's important because this one gives you guaranteed access, as you can see here, to the AI controller and the actor that's running that component
01:58So, let's say I want to do an NPC with this
02:01I'm going to click on that and we'll do NPC generic
02:11And let's open this up
02:11Let's explain what you're seeing here
02:14So, there's three sections
02:16You've got the asset details tabs on the left here
02:19You've got the state tree in the middle
02:21And you got the details panel on the right
02:22The details changes based upon what you have selected
02:24Most most importantly is our state tree in the middle here
02:28Now much like heavy trees, you do start with a root node and that's very important because that's where you start
02:35Now you can add new states by clicking on new state and you can see it's going to add another state here
02:40And take note of the hierarchal design of a state tree
02:42This is what is determining what should go next
02:46So the root will go into one of its its first child, evaluate it and then run that one and if it's got two roots uh it has two children in the root if it fails this one it will then go to the second one
03:01Okay and so on and so forth
03:01Now these can also have their own sub uh children states as well
03:06So if I want to do add state child state as you can see it's going to make a child of this one
03:12Now to order for this third none, this one here, this one I've got selected here, for that to in order to run, it has to be true for the first one, it's parent, and then true for itself
03:28This is what we call a leaf node
03:30In other words, a tree will keep going down branches until it finds a leaf
03:34And the leaf is what executes
03:37At the end of the leaf, you'll see it says root with a little arrow pointing up
03:42This is the default transition rule
03:44So what happens when it ends the leaf here? It was a transition to the root
03:49Go back to the beginning
03:52Now one thing to note about this is that you can actually change this to be wherever you want
03:55So we can change it to transition to other things by using the transitions tab on the details
03:59So, one thing that's good about state trees versus behavior trees is that you have full flexibility about where to send different states based on different upon different conditions
04:11And you can have multiple transitions too
04:12So, you can add one here
04:15You do another one for different things
04:17So, this is a trigger for when the state's completed, but you can do one for when the state's failed
04:21It will do a different thing
04:21Okay? So, you got lots of different extra options to choose from when dealing with transitions
04:32Speaking of details panel, let's take a look at what you have available to you
04:35So, first up, we got the parameters
04:35The parameters are just variables that you assign to your tree
04:39So, let's say for example, we have a vector and let's rename it and we call it location
04:50There's the parameter for the location
04:52Okay
04:56And we can promote that to the parameters in the global parameters
04:58And now it's going to appear in the parameters for this state tree
05:04So I can actually set it now from outside the state tree over here
05:15The enter conditions are your conditions for when it should enter that state or leaf
05:19Pretty simple
05:19You can do various different comparisons
05:22So you got ones that are built in here such as ball compare, float compare, integer compare
05:27Check whe tags
05:27So state trees work really well with game tags built in
05:32It's great
05:32You can also make your own conditions as you can see from the top button up here
05:38Then you have the selection utility
05:40This is determining when it should select that one leaf or branch
05:44Uh by default you have a waiting associated to it
05:46Uh but you can add other things to it as well if you wanted to
05:49So let's say you want to do an enum input
05:53and it'll do like a selector basically based upon the enum entry
05:57Just delete that
06:00Then we've got tasks
06:00Tasks are your meat of your uh state tree
06:02This is where all the code executes for the various different tasks that you want to happen
06:09Then you got transitions which we've seen already what they do
06:14On the left hand side, we've got details about the asset itself
06:17So this contains information about the entire state tree including its parameters
06:20So global parameters that belong to the state tree as well as evaluators and global tasks
06:28More about evaluators and global task in another video, but we'll come back to those soon
06:34One thing you'll note though is because we chose the state tree for AI, you got access to the actor context and the AI controller that is running this state tree
06:43Really good and handy to have
06:47So how do you actually apply a state tree to an actor? Well, let's go ahead and create an NPC
06:55Create new character
06:58And in our character, we'll give it a mesh and an animation
07:07Bring it down there like so
07:13And we want to give it the AI controller as well
07:16So, let's go ahead and create an AI controller
07:24like this and assign it to our class here
07:37It's actually AI controller and AI MPC
07:40There we go
07:40So, this is now using that controller
07:43So for the controller to run the state tree, we're going to go into the controller add and search for state tree
07:51You want to choose state tree AI
07:55Now on the right hand side, you can choose what state tree you want it to run
07:58So we're going to choose our one there
08:00And as you can see, we can plug in values straight away from the location here
08:04You all comes through and gets pulled through
08:06So everything you make global as a parameter will access and reach over from the actor side of things
08:13So you can send other information through if you want to use it
08:16Very handy
08:19And also note that it says start logic automatically
08:22This means that yes, it will start automatically
08:24You don't have to call run behavior tree like you would with behavior trees
08:28It'll just run
08:28But you don't have to do that if you turn that off and want it to start when you want it to
08:31We can just drag out a state tree there and tell it to start logic
08:36Something simple as that
08:36Okay
08:39So we're going to turn it on to be automatic
08:43and compile and save that
08:45Okay, so let's put our NPC in our scene here
08:51And we still need a nav mesh
08:51So let's put a nav mesh in there
09:07Let's check out with P
09:07There we go
09:10So the nerve mesh is what determines where the AI can travel to
09:13So very important that you have that
09:15P on your keyboard will turn that preview off and on so you can see if it is covering the level as intended, which it is
09:25Great
09:25That's the basics of a state tree
09:27Now, obviously there's lots more to cover
09:28We'll be covering that in the future videos
09:30In next episode, for example, we'll be making our AI characters run around randomly using a state tree to control their behavior
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09:53Thanks for watching
09:56Make sure you subscribed and I'll see you next time
09:57Bye, everyone.
