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‫Hello and welcome.

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‫In this lecture, we're going to be getting a line of sight to our player from the enemy so that we

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‫are able, as the player, to hide behind obstacles and not have that enemy followers not have it.

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‫Keep aiming at us until we pop back out and are visible to them.

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‫So you can see here I've hidden behind a corner and he can't find me.

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‫Let's dive in and see how this can be done using unreal tools.

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‫So it's not ideal that this enemy A.I. can currently follow us round corners.

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‫No matter how far we go out, no matter how much we hide behind pillars, it's still going to find us.

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‫It's still going to come and keep aiming at us.

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‫We want to correct that, and we're going to do this by checking the line of sight from the enemy to

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‫the player.

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‫Now, as many things here in Unreal, there is already a function for this in the eye controller called

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‫line of sight.

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‫And if you go and search for that, you can find that there's a function that returns a boolean.

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‫So telling us whether or not we have line of sight and then it takes the actor that we should try to

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‫check for line of sight to, and it automatically takes into account things like the eye position of

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‫the pawn in question.

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‫All this stuff is already coded into Unreal is really cool, so it should be fairly straightforward.

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‫If we go over to our AI controller DHCP, what we basically want to do is change things up in TIC so

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‫that we first of all do an if line of sight.

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‫Then what we want to do if we've got line of sight, is we want to move to and we want to set focus.

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‫However, if we do not so in the else, what we want to do is clear focus.

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‫Remember, we saw that function before and we want to do the let's see the stop movement, basically.

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‫And that's another function that exists that we haven't seen yet.

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‫So what I'm going to do here is I can challenge you to implement the whole of this yourself if you feel

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‫confident.

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‫Otherwise, this else is the more complex bit that we haven't seen before because the other two, we've

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‫already done a move to actor, we've already done our set focus, we've done that before.

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‫And there's just this if line of sight, which we have just seen.

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‫It's pretty straightforward.

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‫You could implement that.

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‫But how about this else?

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‫Let's give a go at implementing the just the ELT clause.

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‫It's not going to compile because you obviously need an if before an else, but let's go and just write

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‫out the ELT clause.

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‫So the first thing clearing focus, basically we're saying stop trying to track the player because you

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‫can't see the player.

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‫You shouldn't be giving off the impression that you know where the player is, even though the eye obviously

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‫can, because it can access the player's location and so on and so forth.

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‫But we need to give the illusion that the AI only knows as much as it can see.

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‫So what we're going to do is we're going to call to clear focus.

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‫And if we go over to the AI controller H and have a look at clear focus, you can see that it takes

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‫in the priority that we need to clear.

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‫Now, a reminder that these priorities are basically different levels of focus.

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‫So we have typically default movement and gameplay gameplay being the highest priority thing.

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‫And what we set by default is gameplay priority.

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‫So what we want to do is clear the gameplay priority, which means that if we have focused based on

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‫movement, for example, if our eye then wants to move back to its guard point, then that focus will

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‫not be cleared and it will be off moving back to its guarding point.

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‫So that's the way focus works.

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‫That's the way the priority system works there.

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‫So what we just want to do is copy this a focus priority code on colon gameplay, and that is the priority

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‫that we're wanting to clear on this line here.

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‫And then the other thing is to stop the movement.

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‫So we want to go over to the AI controlled RH again and have a look at the stop movement.

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‫And sure enough, there is a simple no arguments function called stop movement, which allows us to

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‫do just that.

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‫So there you go.

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‫That is basically the statement written.

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‫So now just reminds it remains a challenge for you to implement the if portion with the if line of sight

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‫and the move to and set focus.

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‫And you basically want to remove this code here.

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‫I'm just going to comment it out and sort out where you want that to be.

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‫So pause video.

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‫No challenge, slide here.

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‫Just go and implement these three lines for yourself.

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‫Okay.

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‫Welcome back.

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‫So let's start with that.

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‫If so, if open brackets line of sight to and then we want to do line of sight to the actor, which

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‫is the player pawn that we want to get access to.

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‫So let's just uncomment that player pawn here and it's mucked up our indentation a little.

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‫Let's fix that.

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‫And then we want our brackets, our curly brackets here, and we want to do a move to actor.

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‫Well, in fact, we can just copy and uncomment our move to actor here.

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‫And we want to uncomment it.

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‫Yes, there we go.

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‫And the focus, we can move that as well.

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‫Now, the focus, it doesn't matter whether you do it before or after move to actor, because while

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‫move to actor does set a focus, it sets a lower priority, the movement focus rather than the gameplay

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‫focus.

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‫So it doesn't matter which order we do those two operations in.

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‫And then finally we can remove this commented out line where we were getting the player pawn in begin

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‫play because we no longer need it and everything's in tick now so we could remove begin play.

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‫I'm going to leave it around in case we need it later on just to save me the hassle of adding it back

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‫in.

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‫Let's head over to Unreal and compile and when that's done, let's play.

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‫So let's see if we can hide from this actor.

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‫I'm going to try and move around the corners reasonably quickly.

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‫This is a little bit tricky because they can move just as fast as you can, but if you get round a corner

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‫like that, they go, He's lost sight of me.

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‫He's stopped trying to chase me.

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‫I can just peek around the corner and see that as I'm moving.

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‫He's not changing his aiming because we've cleared the focus.

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‫Can peek around the corner from the other side.

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‫Let's see.

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‫Pick round over here.

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‫There you go.

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‫You can see he's still aiming at the last location where I was.

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‫But if I pop up into sight, then he carries on aiming and moves within the acceptance radius.

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‫Talking of which, I want that acceptance radius to be configurable by the designer.

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‫So let's move it into a new property.

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‫I'm going to create a private section here with a new property.

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‫Which is going to be an edit anywhere.

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‫And we want that to be a float called acceptance radius and give it the default value of 200.

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‫And then this acceptance radius we can go ahead and use in our move to actor.

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‫And if you compile that, it's going to give you exactly the same behavior, except now that you can

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‫change that in the AI controller blueprint.

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‫So that's it for this lecture.

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‫We have discovered that line of sight function, allowing us to check whether the eye can or cannot

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‫see something.

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‫And we've implemented this basic hiding functionality so the AI doesn't follow us when it can't see

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‫us.

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‫Next lecture.

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‫We're going to take things up a notch from this custom programmed AI and use behavior trees.

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‫A really powerful tool in unreal to make our AI's just that much cooler.