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‫Hello and welcome.

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‫In this lecture, we are going to be starting to add even more functionality into our behavior tree

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‫by adding a custom task, this clear blackboard value, we're going to make that entirely custom in

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‫C++.

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‫Let's dive in and see how to do it.

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‫Okay.

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‫So I'd like to expand out the behavior of this behavior tree so that we can get to investigate.

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‫And once we're done investigating, we move on to going back home.

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‫So I'm going to add a little move to task here afterwards, which just returns us to the start location.

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‫And what we need to do in order to get there is to have some notion of whether we've already visited

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‫the last known play location.

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‫And the way I'm going to do that is essentially by setting the last known player location once we have

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‫investigated it now, if we don't currently have a way of doing that.

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‫But first of all, let's create the decorator.

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‫So add a decorator to investigating Blackboard that is going to be going to go and rename it to has

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‫investigated like so and this is going to check if the last known location is set.

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‫And that means that we need to have some sort of node that allows us to unset a blackboard key.

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‫Now that doesn't actually exist.

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‫You just thought it does, but it doesn't.

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‫So this is a great opportunity for me to show you how we can create a custom task.

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‫Now, you could do it very easily using Blueprint, or I'm going to show you the slightly harder way,

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‫but the one that gives you a lot of power, which is doing it through C++.

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‫So we're going to go over to our main content browser, go to add new and go to new C++ class and we're

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‫going to want to show all classes checkbox.

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‫And then we're searching for Beat Task and there's a lots of options here.

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‫You can see a lot of them are actually those built in tasks such as make noise or there is a move to

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‫here or wait.

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‫Now you could go and have a look at the C++ to see how those are implemented.

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‫That's always useful, but what we're interested in is what should we inherit from?

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‫What should we use as the basis for our own node?

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‫Now there's a couple of options here.

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‫You could choose to have a task node as your basis, or you could use the blackboard base.

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‫Now what's the difference between the two?

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‫Let's have a quick look.

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‫So move to actually uses the blackboard base.

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‫And what that means is that it has this blackboard key dropdown that allows us to choose a blackboard

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‫key to work with.

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‫That means we don't have to hard code into our task the blackboard keys that we're working with, which

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‫is great because it allows us to reuse those tasks in different situations.

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‫So if you need a blackboard key, then the blackboard base is a great one to go with, otherwise you

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‫use the other one.

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‫So let's go and add new add a new C++ class again, show all classes and we're looking for the beat

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‫task again and we're selecting the Blackboard Base hit next.

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‫Now I'm going to rename this to Beat Task, Underscore Clear Blackboard Value and we're going to go

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‫ahead and create that class here.

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‫Now, initially, this will fail.

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‫So let's click yes and see what the error message is here.

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‫It's saying something about Link, which stands for Link, unresolved external symbol, blah, blah,

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‫blah.

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‫Usually when you've got this kind of error from the linker, this is saying that you've got something

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‫in your header files that wasn't in your C++ or in this case it means that there isn't a module included

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‫that we are relying upon.

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‫And based on the types of symbols that it's looking for, I can see here it's the AI gameplay task owner

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‫interface.

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‫It seems to be looking for something to do with gameplay tasks and that is a module in actual fact.

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‫So if we go over to our Visual Studio code and just open up the file browser, it's just going to scroll

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‫up to my project.

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‫Then under source simple shooter.

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‫There should be a simple shooter build X or whatever your project name is, build.

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‫And in here, if I give us a little bit more space, you can see that we've got this public dependencies,

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‫module names and the module name here that we want to add to this list is going to be game play.

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‫Tasks with an S and if we go ahead and add that and go back and compile now, hopefully everything should

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‫compile successfully for whatever reason.

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‫This doesn't automatically get added when you override for a boot task.

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‫Now once that's done, let's go and have a look at what was created here.

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‫We should have a new class, which is our beta task, underscore clear blackboard value and it's pretty

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‫empty at the moment.

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‫Now what I want to do is if we were to add this in to our behaviour tree at the moment, it would have

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‫an ugly name.

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‫So we want a nice human readable name for this task.

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‫And the way we're going to do this is by adding in a constructor and setting a property.

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‫So let's create a public constructor here.

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‫The constructor always has the same name as the class so we can copy that.

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‫Doesn't need to take any arguments semicolon at the end and then let's create the implementation over

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‫in the C++.

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‫And the implementation just needs to set a variable called node name.

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‫So if you set node name and then you use a string, then the string that we set is going to be the node

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‫name.

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‫So it's going to be clear blackboard.

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‫Value just with the spaces and the correct capitalization should be nice and easy.

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‫Now, one thing that I forgot to do at the time of recording is to surround this by the text macro.

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‫Now you should go ahead and do that in your code, but you'll see that in my code.

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‫It will persist in just being like this, and we should be able to go and compile that now.

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‫Awesome that compiled successfully.

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‫So I challenge you to add this new node.

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‫So add it to the end of the investigation behavior and just check that it completes.

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‫Basically, it should automatically complete without doing anything at all.

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‫But check that the name is correct.

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‫Check that you're able to add it and we'll look at adding the behavior in the next lecture.

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‫So pause video and have a go.

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‫Okay.

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‫Welcome back.

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‫So let's go to our enemy A.I. and add in at the end of the investigate behavior.

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‫We're going to add in our clear blackboard value.

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‫You can see it's got the nice name there.

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‫And you can also see that if you go over to the details pane, you can select a blackboard key.

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‫We're going to select the last known player location.

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‫Even though that doesn't do anything yet, you can see that we have that functionality because we inherited

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‫from Blackboard Base and let's just check that it completes automatically.

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‫It should do and then it should move on.

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‫Let's move it on to a weight task afterwards so that we can see that just goes straight through or completes

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‫automatically.

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‫So I'm going to play I am going to go and hide myself around a corner as much as I can, and then I'm

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‫going to go and have a look at the investigating it went through and actually he's seen me.

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‫So let's go and hide again.

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‫Go and hide around the corner if I can.

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‫I would go and then I'm going to go to the.

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‫There you go.

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‫It's gone right through the clear blackboard value, which must mean that it succeeded, because we

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‫know that if it was a sequence and it failed, it must have it will have stopped and not gone onto the

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‫weight.

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‫So that's working correctly.

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‫The clear black world value is just returning success straight away and going on to waiting the next

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‫lecture, we're going to look at how we can actually add in the functionality.

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‫I'll see you there.