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‫Hello and welcome.

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‫In this lecture, we're going to be introducing a new thing in the behavior tree, the services.

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‫We're going to find out what services are, how they help us with persistent running behavior and how

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‫we can write our own in C++.

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‫Let's dive right in.

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‫Now there are only a few pieces of logic left in our AI controller that aren't in our behavior tree.

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‫One of these is setting the start location.

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‫This I still want to set here from the I controller.

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‫But things like tick now that I would like to do from within our behavior tree.

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‫What do I want to do here?

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‫How do I get it to do?

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‫Set our player location to update the last known player location.

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‫Both of these we can do with something called a blueprint service.

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‫So let's go over to our blueprints and see what's going on.

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‫So if I go to my AI and open up the behavior tree, dock it to the main window, then I need to show

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‫you what a service is.

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‫We've never used one before, and it's essentially a way of running something every tick or every so

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‫often whenever a particular path is active.

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‫So if I had a service here on the Chase behavior, then something would some code would be able to run

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‫all the time that the Chase behavior is active, whether we're moving, shooting, weighting any of

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‫these things, it would always be running.

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‫But if we're in investigate it would not be.

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‫So this is exactly the kind of situation that we're looking to use a service.

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‫Now let's have an example service.

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‫One thing that we notice when we're playing is that the once the AI comes within range of us and we

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‫move around, he's not rotating to look at us and we can fix that with an already built in service here.

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‫So if we right click on this node and go to add service and look for the default focus service, you

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‫can see it's a different color, it's green.

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‫And if we select that default service, it also goes underneath these sequence nodes as opposed to above

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‫them, which is what the decorators do.

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‫So with the default focus selected, you can then choose what you want to focus on.

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‫And in this case we want to focus on the player location, go ahead and hit save and hit play.

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‫And now if we go and have a look and move around, you can see he's rotating to follow us.

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‫Cool stuff.

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‫Now we want to be able to implement a similar service in C++ that will update our player location all

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‫the while and update our last known player location while we are chasing.

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‫So we're going to do that as two separate services and you can see how that also automatically services

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‫can make things a little bit more efficient than doing it in tick because you can only run the last

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‫known player location when you're in the right part of the behavior tree.

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‫So let's go over to the sandbox, go to content browser, add new new C++ class, going to show all

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‫classes and look for what our options are here.

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‫We're looking for BT service and then there are a couple of options just like we had with our BT task,

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‫we've got the Blackboard base and we're actually going to want the Blackboard Base because we want to

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‫know which key we should be updating.

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‫For example, should it be the player location?

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‫Should it be the last known player location?

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‫So we're going to go and hit next on this one with the Blackboard Base selected and we're going to call

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‫this BT service, underscore player location like so and go ahead and create that class.

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‫So once we're done compiling, we're going to go over into Visual Studio code and you can see that we

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‫have got this BT service player location which is inheriting from the Service Blackboard Base Call.

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‫That's what we wanted.

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‫Now what functionality we're going to move into this?

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‫Well, I'm going to try and move the simplest functionality possible, which is just to set the value

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‫of the basically the last known player location.

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‫Though this key will be configured in the behavior tree, not here in a plain text, but it's going

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‫to get the player -- location and set it to a blackboard key.

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‫And it's not going to do any of the line of sight checking reason being if we are running it in our

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‫behavior tree only when we are chasing then we don't need the line of sight check.

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‫We can see the player that's automatically we know that's the case.

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‫So another simplification there for doing it in the service.

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‫So this should be fairly straightforward if we know how to get a method call here in the BT service.

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‫So let's go and have a look at our BT service to see what is available there.

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‫What's the documentation, what can we do?

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‫The main methods here you can see are on become relevant on C relevant the tick node and on search start.

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‫On search start.

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‫We're not particularly interested in but tick node.

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‫Yes, that is where we're going to get an update all the time that this service is on an active path.

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‫So that's when we're going to want to implement.

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‫We go and search through this file to find the full signature here.

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‫We can see it is here.

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‫Let's see, what section is it in?

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‫It's under the protected section.

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‫So we're going to go to our BT service that we've created and create a protected section.

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‫And paste in, it's automatically an override here because BT Service was inheriting it itself from

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‫a parent class, but it's no harm in overriding it again ourselves.

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‫We can do a control shift P to create the implementation and then we want to call to super.

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‫So we want super tick node and we want to pass in our own comp and our node memory.

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‫And let's see, there's some other things in here.

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‫We have a Delta seconds as well as what we need to pass up as well and finally finish off with the semicolon

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‫should finish off our implementation of tick node.

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‫Now in here we basically want to do that behavior from the I controller CP, the one where we are getting

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‫the blackboard component, then setting a value as vector.

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‫Well, we know how to get blackboard components from owner component references.

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‫So that's pretty straightforward.

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‫We're just going to do the owner comp dot and then we're going to do the get blackboard component remembering

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‫that we need to hash include in here for the behavior tree forward slash blackboard component.

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‫Then we can use our arrow operator.

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‫And what we should be able to do here is just to set value as vector and then we need a key.

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‫Well, we know how to deal with this, but let's just refresh our memory.

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‫If we go to our BT service underscore Blackboard Base, you can see same as with the task, we've got

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‫the get selected blackboard key.

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‫That's what we're going to use.

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‫Get selected Blackboard Key gets the key that was selected over in the behavior tree and then we want

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‫our vector value.

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‫Where are we going to get that?

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‫We'll exactly the same as the AI controller.

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‫We're going to be getting the player -- first and foremost up here at the top.

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‫Then we need to check whether or not this is null and we also need to include our gameplay statics.

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‫So let's make sure we have the gameplay statics include from the controller CP included in our player

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‫service player location.

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‫Then we're going to do and if the player pawn is equal to null pointer, then what we're going to want

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‫to do is again return early here it returns void so we can just do a quick early return.

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‫Then we can use our player pawn here to simply get the actor location and we may need to do an include

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‫here.

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‫We'll see how we go.

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‫Well, it doesn't hurt to be safe, does it, and explicit about these things.

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‫So we're going to do a include for the game framework and then forward slash.

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‫It's going to be pawned on H so that we can make sure that we've got everything in order here and then

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‫we're just setting the value as vector.

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‫That should be all we need.

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‫Let's go and compile and see if this works.

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‫In fact, one more thing.

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‫We probably want a nice pretty name, so we should have a constructor here.

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‫So I'm going to create a public section with the constructor, which is going to be the name of the

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‫class, and then we go ahead and create that implementation.

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‫I'm going to bring my implementation above the implementation for tick node and then we're going to

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‫have set the node name equal to it should be update player location and let's build and see if that

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‫works.

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‫Looks like I had a missing semicolon.

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‫Let's try that again.

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‫Once that's compiled successfully, we can go over into our enemy.

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‫I and as well as the setting focus, want to add a new service which we've got showing up here as the

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‫player location which where the pretty name basically comes up as update player location.

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‫You can see that it wants to it tells you the frequency of ticking every 0.4 to 0.6 seconds.

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‫That's better than using tick because we know tick runs every frame here.

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‫This is running less frequently, which is a good thing.

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‫And we can go over into the details and create a blackboard key, drop down and select that we want

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‫to update is not only the player location but the last known player location, because that will happen

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‫every frame as long as we are chasing and that is the behavior that we want.

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‫So one more service node we want to go ahead and create is going to do the AI controller's behavior

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‫for going down into to tick and see what's left.

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‫For us to do here is to update the player location conditional on whether we have line of sight.

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‫So we want it to update the player location.

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‫If we have line of sight, clear the location if we don't.

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‫So that's going to be a new service node because it's a slightly different behavior.

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‫We're going to add new new C++ class.

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‫We're going to go to show all classes and again, we're going to do BT service, underscore blackboard

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‫bases, our base class, and we're going to call it Beat Service Underscore.

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‫Player location if seen.

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‫And go ahead and create that class.

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‫And because this is all stuff you've mostly seen before, it's going to be your challenge to implement

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‫this service.

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‫So you're going to implement tic node using the code over in the AI controller.

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‫As your guide, you're going to need to get hold of the AI controller pointer from within the BT service.

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‫Now this is exactly the same as we did in the BT task, so use that as a guidance for getting hold of

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‫that AI controller pointer.

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‫You'll need the AI controller pointer in order to check for line of sight.

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‫Remember, line of sight is a method on the AI controller and then you need to update or clear the key

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‫depending on your line of sight check and then place this node in the behavior tree.

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‫Where do you think is going to be the right level of the behavior tree for this service to run?

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‫How will think about that?

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‫Had a little bit of a chin scratch, pause a video and have a go.

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‫Okay.

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‫Welcome back.

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‫So this has opened up a new beauty service over in Visual Studio code.

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‫Now it's pretty much going to be identical in the header, so I'm going to go ahead and copy that over

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‫into our newly generated header, the exception being that we need to change the name of the constructor

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‫to match.

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‫Now we're going to create an implementation for the constructor and give it a node name to update player

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‫location if seen and add a semicolon on the end here.

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‫Let's not forget that this time.

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‫Then back into the C++ going to implement tick node as well and I'm just going to copy across if we

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‫can find ourselves the player location.

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‫CP And just going to copy across the call to super and the getting of the player pawn and the checking

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‫of the null return.

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‫In fact, I'm going to copy the whole body and we're going to modify it from there.

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‫So copying that across and also we're going to be copying the access to the blackboard component with

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‫the include for the blackboard component, the gameplay statics and the pawn, because we need access

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‫to all of those.

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‫In fact, much of the functionality is shared here.

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‫You could think about having them somehow share this code, but I think there's not so much duplication

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‫that we care enough.

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‫So what we going to have to do here is also check that we have an eye controller.

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‫So I'm going to do an if the owner component or owner comp dot get I owner is equal to null pointer,

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‫then we're going to want to go ahead and return at this stage.

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‫Then the next thing we're going to want to do is check our visibility.

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‫So we're going to do an if owner comp dot get I owner and then we're going to do an arrow here and we

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‫need to include our controller here.

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‫So it's going to be hash include.

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‫And then it's going to be I controller H.

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‫Then we want to do line and let's see what's the correct usage here.

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‫If we go over to the I controller CP, it's line of sight two is what we want.

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‫So line of sight two then we need to do line of sight to the player pawn.

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‫In this case, do we have line of sight to the player pawn?

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‫Is that what we're doing over in the CP?

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‫Let's just double check that.

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‫Yes, we are.

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‫Then we're going to want to go ahead and set the values differently.

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‫So we're setting the vector value to the player pawn get actor location.

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‫Yes, that's if we've got line of sight else.

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‫If we do not have line of sight, we know that we need to be clearing that value.

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‫So we're going to be still getting the owner component, get blackboard component.

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‫Then it's going to be clear value and we're going to be clearing the value of the selected blackboard

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‫key still, and that should pretty much cover us for the implementation of player location.

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‫If seen, let's go and compile and see if it works well.

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‫The compilation succeeded.

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‫Let's go in to the behavior tree.

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‫Now the level I want this to run at is basically at the top level in the initial selector, because

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‫I want it to be updating the player location basically all the time because we need to be able to abort

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‫any of these other behaviors based on the player location being set.

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‫So we need to be able to set an unset it at any time.

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‫So I'm going to go and right click on the top level selector, add service, add the play location if

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‫seen.

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‫And then we're going to need to select that service node and select its blackboard key, which is going

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‫to be our player location.

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‫So that one set in the player location, the update player location, the more dumb one is updating

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‫the last known player location.

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‫And we should now be able to go down to our AI controller and essentially remove all of this code in

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‫TTIC because it's been superseded by our services instead.

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‫And we can go ahead and compile and see if that works.

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‫Let's go over to the editor and play and see if we've still got our enemy coming up to us.

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‫He's coming running to us, loses sight, then comes back at us, starts shooting.

213
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‫Yep.

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‫Basically everything is working as it was doing before, except now it's doing it entirely via services

215
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‫that we wrote for ourselves in C++.

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‫Next lecture, we're going to be fixing that pesky bug where the AI continues to shoot and eventually

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‫manages to kill itself off.

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‫I'll see you there.