00:00What's up guys, welcome to a new Unreal Engine 5 tutorial

00:01Today, I'm going to show you how to use state trees to build your AIs

00:06It's going to be very easy to follow, so let's get started

00:08All right, so first of all, what are state trees? Well, a state tree is a tool that controls the behavior of actors, pawns, or just AI in general by organizing different actions, which are called states, and the rules for switching between them, which are called transitions

00:24So, with that said, let's go ahead and enable the state trees plugin

00:28Go up into Edit, Plugins, and search for "State Tree." As you can see, we already have State Tree enabled

00:37But we do also need to enable gameplay state tree

00:39Just go ahead and take this, and then click on "restart now." Okay, so the project restarted, and now we have the state tree plugins that we need enabled

00:48So in the Content Browser, let's right click and go inside of the artificial intelligence section, and select state tree

00:55On here, we have different options for different classes

01:00In this case, let's select the state tree component, which is simply the default one

01:04Let's call this "store enemy AI" and open this up

01:07So as you can see, we have different windows over here to build our state tree

01:14Let's go ahead and go from left

01:17All right, so first of all, we have the asset details, and here is where we customize all the properties about our state tree

01:23So, for example, the parameters, evaluators, global tasks, and so on

01:28In this video, we will not deep dive into aerators or global tasks, we will simply cover parameters and the schema, but overall, this section allows you to define some properties that you need for the state tree

01:40Next, we have the states window itself, and this is where we, you know, create the actual logic blocks for all of our states and all that stuff, and lastly, we have the D panel, which essentially displays all of the

01:56Properties about that specific state that we have selected, so with that covered, let's go ahead and begin creating our first states

02:04So for this AI video, it's going to be very, very simple

02:07We are simply going to go ahead and make sure that an AI can chase us and then simply play an attack animation

02:14So let's go ahead and add a new state, and as you can see, it added a new blog right below the other blog which we had, which was root

02:24As you can see, it also added some indentation because this root block over here is the parent of this other's

02:29We'll get a bit more into detail about the difference between just having parents and Just, you know, normal types of, um, you know, tasks and states and all that stuff, but for now, let's simply name this to "chase player" because this will be the state for chasing the player

02:46So, as soon as our AI enters in the state, it will simply go ahead and follow the player in the world, as simple as that

02:52Let's go ahead and compile and save

02:55Now, when we select this state of here, as you can see in the D span, we have all these parameters that we can configure, for example, the name, the tag, the color, the type, and all this stuff

03:07Now, in this case, once again, it's a simple overview of state trees, so I'm not going to go ahead and go too much

03:14Into detail about all this stuff, but only so that you know the type will always be state for 99.9% of the cases

03:22This is the default type of logic that we would use for AIs and many other stuff, so pretty much you will never need to touch this parameter in your life

03:33And then the same with selection behavior, we can leave this by default on what it is, don't worry about that

03:37So the most important points about the individual states are the enter conditions, the tasks, and the transitions

03:49The enter conditions are essentially the rules for, you know, the logic to enter into the state and of course execute whatever

03:57Is inside of this state, the test is the actual logic that executes, so it will be linked to a blueprint graph where we're actually putting, you know, the blueprint for chasing the player, play the attack montage, and all this stuff

04:09And lastly, transitions is what, you know, once this task completes, for example, go into the next one or whatever, and all that stuff

04:18Okay, so let's begin by creating the actual logic for this state over here, so if we go to tasks, we can add a new task, but of course, we only have a couple default ones, so we need to create our own custom one to add the logic that we want, which in this case, to chase the player, so

04:34If we go up into new task over here, we can select the default class, and now let's go ahead and name this task "Uncore Chase Player," as simple as that

04:46Let's go ahead and open this up, and as you can see, it's simply a blueprint graph

04:49Now, this would be very similar to our tasks in behavior trees, it's essentially the same thing

04:55So, we need to go into the function section over here, click on overwrite, and now we can overwrite a function

05:02In this case, we want to overwrite the enter state, so as soon as the AI, we enter into this state, we execute the following code, so I can make it very simple where I simply type print stream and We print hello, but let's go ahead and just fully make the code, which is going to be very simple

05:21We're literally going to use the AI move to node from Unreal Engine, and we just need to put in a pawn

05:29This pawn is the one that has to move, so we need to reference our enemy AI blueprint

05:34We can do this by just creating the variable, call this AI pawn, and on the type, simply set this to be pawn

05:44It's going to be an object reference

05:46Now, very important, let's click this eye icon over here, so it is instance editable, and that means that we can access it from outside in our state tree

05:56With that said, let's drag this, get, plug it in, and of course, the The AI actor will be, well, the get player character in our world

06:05Let's put the acceptance radius to 120, so it doesn't get so close to me, and on success, we can add this finish task

06:14Now, over here, copy and paste this, put this in the other pen, disable this, and boom, there we go

06:19So, as simple as that, once the AI reaches the destination, we will finish the task, so then the state tree can consider the transitions, condition, and all that stuff to go into the next tasks that we need

06:31So, with that done, we can close this, go to the chase player task over here, and add a new task

06:38As you can see, now it shows up, we can select this task, and as you Can see we have the variable exposed, this is the AI pawn variable that I created, so it is as simple as going into this bind property here, and we can promote this to a variable, but we don't want that, we want to actually bind it with a default feature of state, which is really cool

06:58As you can see, we have a default variable, which is actor, this is essentially the, you know, actor of our enemy AI, this is the actor who has the state tree, so we drag the, and open the schema, we can select the class of our enemy AI, this is really, really cool, we only have this in state trees, we don't have this in behavior trees or other stuff, so first of all

07:21Of course, I need to create a blueprint class for my enemy AI

07:26We don't have this, so let's right click, quick, go to blueprint class, select character, and name this BP_EnemyAI

07:32Open this up

07:37I'm going to make it very simple, just add in mesh, which is going to be, for example, Man Simple

07:42This is going to be minus 89, minus 90, so it's on position

07:46Anim class going to be a many compile and save

07:49And now we also need to do one thing in our enemy AI to execute the state tree, which is to add a component, and of course, we need to search for state tree and add state tree, not AI, because in this case, we use the default class, okay, so state

08:06Tree enter, and then on the parameters, we select the one that we created, okay? So this is how we add the state tree into our enemy AI to be able to be executed and all this stuff

08:16Close this

08:19So now, on here, we can search for enemy AI, and boom, as you can see, this actor variable updated, which means that now we have direct reference to the enemy class, which allows us to go back into the task, into the dis Spano, and bind this to the actor, and that's it

08:36Now let's drag this enemy AI into the world, and if we press play, nothing happens

08:42This is because we need one important thing to make AIs working on R engine, which is a nav mesh, so we Go to the "quickly add to project" section, volumes, and drag a Nav Mesh Bounds Volume to our level

08:54We can click the "Cell Size" and put this to 20

08:57Now, we press P on our viewport

09:00You can see these green areas highlighted

09:03This is where the AI can go, and this is how Unreal Engine calculates the possible paths that our AI can navigate through

09:09We press play

09:11As you can see, the AI is chasing me because, as you can see, we only have one state

09:16As soon as the route enters into this state, which is automatic, we execute this logic, and as you can see, it is working just fine

09:23We are executing our task, which is to chase the player, and everything Like that, as you can see, it's very, very simple, but it is working correctly, which is really, really cool

09:34Now, first of all, I might need to do some modifications to the enemy AI

09:36He is a bit too fast

09:39Let's go to the character movement, scroll down, and enable "Orient Rotation to Movement," so his rotation is a bit smoother

09:47Let's also go back up and set the max walk speed to around 500, and then last but not least, is go to class defaults, search for "Yaw," the "Orient Rotation to Movement," save, and now he will go a bit smoother, as you can see, when he's walking

10:07We still don't have the animation set up, we'll do that a bit later

10:09That's like extra stuff

10:12The main focus of the video is the state tree, but you get the idea

10:15Everything is working fine

10:16Okay, so back in our state tree, let's go ahead and add another state to attack our player

10:21Okay, so once we have completed this Chase player State, and he, you know, reached our destination, we need to play, of course, an attack animation, and we can do this through another state

10:34So let's add a new state, and let's call this attack player

10:38Let's compile and save, and as you can see, we are adding this attack player also as a child of root, so root is the parent of this too, but if we want to have things a bit more Organized, we can even create categories, so if I add another state, I can call this, for example, "on seeing player." Okay, so imagine that when we are seeing the player, we enter into this aggressive kind of state, and we want to do this, so we can simply put this state, um, up over here, and then make this a child by just dragging in

11:14Now remember to drag attack here, but as you can see, now we have a category of unseen player, and inside of this category, we are chasing the player and then attacking the player, and this just makes sure that everything is way more organized and have

11:28Also, let's say parent conditions and parent

11:34States, which is going to be very important in a second when we do the different kind of states in terms of idling or patrolling or whatever

11:40So with that said, let's go into the attack player and we need to create a new task, so new task blueprint base, let's call this task underscore attack player

11:55Open this up, as you might remember, we need to go to functions, enter state, and then over here we need to go ahead and play the animation or whatever we want

12:02In this case, I need to go ahead and create a new variable and have the player reference, well not the player reference, sorry, the enemy reference, so we can play the montage, so

12:12This will be like enemy AI, this will be, of course, the enemy AI blueprint, a your reference

12:20Make sure this is enabled, drag this, and we can say play montage, and there we go

12:32Now I need to import some attack animations

12:34I'm going to be using this free animation pack, so I just imported it, and now with this animation, I can right click and create a montage, go back to the task, go ahead and add this montage, and then I can simply add a bit of delay, so let's do like, you know, 0.5 or 0.8, something like that, then I can say finish task

12:56Remember to always, always, always add this node so that our state tree knows when this task has, you know

13:06been completed, so we can continue on with our flow of code, if that makes sense

13:10We can close this, go back to the state tree, and on this tag player, we can add the task

13:16And now, of course, we need to find the actor for our variable, and that's it

13:22Now, as you can see, when we press play, nothing happens

13:24Why is this happening? Well, as you can see, the ch CH play is going back to the route

13:30Once this is completed, we are, you know, knowing this because of this icon, right, the transition to root state

13:35We want to change this, so we can simply select the chase player state at any transation, and when the state has succeeded and we have reached Our destination, we can transition to, well, the attack player, and now when we press play, he goes and attacks

13:54As you can see, everything is working fine, and he continues to chase me and everything like that, so everything is going to head in working, and then of course, when he attacks, we want to go back to route to know and repeat the whole process

14:06Now, on top of this, let's add one final thing, which is going to be the idle state, so add a new state, call this "idle," and this will be on top of everything

14:20Okay, this will be like the, you know, default state in this case

14:23Okay, so of course, the auto state will not play anything if we Press display, it will be just on idle, right? But what we can do is add an enter condition, okay, which we haven't done yet

14:35So the enter conditions are essentially these kind of rules that define when we can enter a state or not

14:44It's not always going to be, you know, from state to state, like automatic, it can be with conditions

14:48So what we can do is add a simple parameter over here, which, you know, just think of parameters as variables

14:55Let's select a Boolean and name this to "is seeing player question mark." So this is a simple Boolean variable, which is called parameters in state trees, and I'm mentioning that we want to play the

15:08Idle state, when we are not seeing the player, but when we are seeing the player, we want to go back to the unseen player, which is the chase and everything like that

15:18So in idle, we can add in a condition, and it's going to be a Boolean compare, because we want to, you know, compare a Boolean

15:25As again, we have invert left and right, so for the left, we can plug in a variable

15:30In this case, we want to plug in one of our parameters, which is "Is Seeing Player," and on the right, we can simply say, okay, is this true or false? In this case, if we are on idle, we want "Is Seeing Player" to be false, so we can leave this disabled, and that's it, but then for unseen

15:45Player, we can add a new answer condition

15:49It's going to be a Boolean again

15:51It's going to be a reference to a seeing player, but of course, this has to be true on the right because we want to enter if we are seeing the player

15:57So right now, by default, as you can see, the same player is disabled, okay? So if I press play, nothing happens, but if I enable this variable and press play, he comes to me because the condition rules are working

16:11So we can use conditions for this kind of things, for example, are we seeing the player, are we not seeing the player, and all of this stuff

16:17Last but not least, I'm going to simply add a little animation

16:22Blueprint for the enemy AI, and boom, now he has some cool animations

16:25As you can see, everything is working just fine

16:27So that's it, guys

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16:41Now yes, with all said, bye-bye

16:50[Music]