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‫Hello and welcome.

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‫In this lecture, we're going to be creating a new component in C++, this trigger box, which will

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‫report to us when we step inside the alcove or we place any object in the alcove.

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‫You can see we're getting a little blueprint message up in the top left hand corner.

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‫And to do that, we're going to have to understand how overlaps and blocking and different collision

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‫responses behave in Unreal.

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‫Let's dive in and find out.

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‫Now we've already become familiar with how trace channels work.

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‫We know that you can have trace responses on the different objects in our scene, such as this shrub.

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‫Here, you can see that it has a ignore response to weapon traces, but it does block visibility traces.

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‫Then there's this bulletproof glass example.

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‫It blocks weapons but allows visibility through and a brick wall which blocks both.

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‫So you can see how this system works with trace channels.

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‫Now, what happens if we're trying to decide which objects can overlap with each other, which ones

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‫pass through, which ones block each other?

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‫That can get a little bit more complicated.

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‫We saw this already when we tried to get the gargoyle to overlap with our pawn.

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‫Now this is how it works.

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‫Essentially, we use these object types.

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‫Each object can belong to can be a particular object type.

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‫And this is different to the kind of type system in C++.

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‫These are collision types.

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‫So you might have object A and object B and in their settings, if we go and have a look at the settings

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‫on our gargoyle, for example, you can see that they have their own object type.

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‫This one is a world static object, but then further down they have their responses to other types of

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‫objects as well.

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‫So you can see that this object will block other world statics, it will block other world dynamics,

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‫it will overlap the pawn types, it will block physics bodies and pretty much block every other type.

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‫And obviously the pawn itself if we go and find our BP player.

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‫And look in its capsule component, look at the details and scroll on down to where it's got a collision

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‫preset.

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‫If we can expand out the Pawn Collision preset, we can't edit it, but we can see what it's doing.

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‫And you can see that it has its own response to world static.

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‫So its response to the world static would be to block it.

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‫So we've actually got two different options here.

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‫The pawn is saying I block world statics, but the gargoyle is saying I overlap pawns.

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‫So what should happen?

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‫Well, this is where this table comes in and I've got a link to this blog post if you want to read it

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‫in full in the lecture resources.

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‫So you can see that it takes the least blocking interaction between the two.

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‫So if the object A was the pawn and we're saying, hey, I should block that gargoyle, but the gargoyles

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‫object B and it's saying, hey, I should overlap that pawn.

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‫So it's going to take the least blocking of those two and it's going to overlap.

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‫So it does mean that if you want two things to block each other, they both need to agree that that's

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‫what they want to do.

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‫So let's look at another example here.

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‫We've got the player which is of object type pawn, and it's object response to other pawns is to block

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‫them and world static objects is to block them.

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‫The brick wall is a world static object.

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‫It can block pawns and block world static.

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‫So these two would agree with each other.

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‫Now the shrub is also world static, but it overlaps pawns.

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‫It's very much like our gargoyle, but it blocks world statics.

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‫So if you go down and have a look at what would happen is the pawn would try and travel through the

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‫bush and it could because it takes the least blocking option, which is overlap and it generates an

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‫overlap event which we can hook into in code or blueprint, whereas it won't be able to pass through

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‫the brick wall and it generates a hit event again, something that we can hook onto in Blueprint or

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‫C++.

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‫So why do I go into all of this depth?

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‫Because what I want to do is put an object that we is basically invisible inside this wall that allows

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‫us to put the gargoyle in here and we get an event when that happens.

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‫So the gargoyle will prop up an event and say, Hey, I've got something overlapping with me.

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‫So why is all of this important?

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‫Because I want to put an object that's invisible but will overlap with the gargoyle and let us know

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‫about that fact.

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‫We can then query it from C++ or we can get events in Blueprint either way.

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‫And the way we're going to do this is, first of all, create a blueprint from this dungeon wall.

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‫So I'm going to click the blueprint button in the details pane, create a new subclass, and I'm going

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‫to name it beep, underscore secret wall and we're going to hit select to create it and a docket to

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‫our main window and it's got a mover on it.

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‫What I also want to add in here is essentially a component which is called a box collision.

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‫So if we click on a box collision, you can see it's completely invisible.

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‫It just gives you some box extents which we can change, we can make them larger so that anywhere we

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‫place the gargoyle in this box, it's going to accept it.

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‫And we can see that it has got collision options down here.

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‫We've got an overlap all dynamic as the default, but as the default preset.

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‫But if we hit custom, you can see we can change the object types and we can change how it responds

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‫to different things in here.

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‫And I think most importantly, as you can see, it's set up to overlap with most object types, which

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‫means that even if they're not set to overlap with world dynamic, it's going to overlap.

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‫It's not going to block anything.

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‫It's going to let us position the gargoyle in here.

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‫So I'm going to go and delete that component from the scene, because what I want to do is create a

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‫new component in C++ based off of that box collision.

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‫Now I just want to show you that with this box, if we set it back to the default preset it was on,

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‫which was overlap all dynamic I believe and we check or as is already checked actually generate overlap

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‫events is already checked.

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‫Then we can go over into our event graph and we can right click in here and look for overlap.

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‫And right at the top you can see an add on component begin overlap for the box.

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‫So if we click that and actually let's rename the box component to trigger area like.

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‫So then basically if we overlap with the trigger area, we're going to get a list of properties of the

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‫thing that's overlapping with us so we could take the.

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‫It's overlapping.

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‫We could get its name.

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‫So get display name is the name of the node.

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‫And then we could take that and print the result string and hook that up to the execution pin and we

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‫can go ahead and hit play.

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‫And if we walk up to the area, you can see that it's saying the beep player is the thing overlapping

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‫it.

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‫Now I can't see that area because it's so dark.

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‫So I'm just going to go to the secret wall again, a beep and I'm going to add in a spot light component,

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‫which I'm going to place in this little alcove, rotating it to face down and illuminating the space

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‫where we want the object.

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‫Now in the scene, we can see it very clearly.

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‫So let's go ahead and hit play and we can walk up to that alcove.

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‫If we overlap it, it says there's the beep player overlapping and we can go and grab our gargoyle from

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‫this cell using our newly minted grabber, and we can take that gargoyle and place it in this area.

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‫However, it doesn't seem to be generating any overlap events, and that's because just like we need,

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‫there's two parties to the collision.

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‫There's also two parties to generating overlap events.

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‫So just because we have it enabled on that box component doesn't mean that the gargoyle moving into

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‫it is actually going to alert us to any overlap events.

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‫So what we have to do is we have to go to the gargoyle and check it, generate overlap events as well.

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‫So then the overlap events should happen.

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‫Let's go and pick up the gargoyle, take him over to the alcove and stick him in.

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‫And now we are getting an event coming up.

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‫When that happens, the Gargoyle statue is indeed being registered.

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‫Now, I don't want to be using blueprint events in this particular case.

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‫So what I want to do is take our trigger area component and actually turn that into some a C++ component

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‫that can evaluate whether it's got the Gargoyle statue at once or not already in it.

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‫The way we're going to do this is we're going to go to the add components, create a new C++ component.

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‫And as the parent class, instead of choosing active component or scene component, we're going to go

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‫to all classes and we're going to search for the box component instead.

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‫And you can see the shape components, box components, the one we want and we can go ahead and hit

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‫next.

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‫So I'd like to challenge you to create this component now that I've shown you how to set the parent

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‫class.

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‫So you're going to name it trigger components and you're going to have to copy some things from the

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‫other components we've created because it's not set up in the same way.

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‫Seeing as we're deriving from a different parent, you're going to have to copy the you class line.

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‫That whole line is basically empty on the trigger component as you will create it.

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‫So copy that from either your grabber or your mover, and otherwise you won't be able to add your components

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‫in to your blueprints.

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‫So then you should use this new trigger components to replace our current box component and print something

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‫from Begin Play.

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‫Again, it big in play won't be set up automatically for you, so you're going to have to copy from

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‫the header file and C++ file of our other components in order to set it up.

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‫Pause the video and have a go.

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‫Okay.

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‫Welcome back.

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‫So I'm going to call it the trigger component.

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‫All one word and hit to create class.

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‫So as predicted you class line is got nothing inside the parentheses and if we go and have a look at

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‫our editor and go to the BP secret wall, try to add this component and search for trigger, you can

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‫see nothing comes up.

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‫And the reason for this is if we went over to our grab a dot H and had a look at its use class line,

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‫you can see that there's a bit in here that says blueprint spawn able component.

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‫So crucially, we need to copy this.

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‫It also has a class group.

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‫We might as well copy the whole thing because this allows us to create this component in blueprint so

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‫we can go and paste this as the class line for the trigger component.

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‫And then the other thing, if we go to grab, you can see it's got big in play, it's within a protected

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‫section and we can just copy the definition of that begin play function, copy it over into our trigger

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‫component and put it as it was in the grabber, just underneath the generated body.

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‫Then we can go into our grab a CP and see how big in play was defined.

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‫In here you can see that it has this cool to super big in play that is actually important.

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‫So we're going to copy that, go over into a trigger component.

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‫CP And we're going to change the you grab a colon colon to you trigger component, begin play.

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‫And then in here we can put in our you log and we're just going to write a simple message such as trigger

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‫component alive and we'll go ahead and compile.

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‫This may take a little while, seeing as we've made some fairly significant changes to our header file.

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‫And once that's done, we can go into our BP secret wall, go to add and search for trigger.

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‫And in here you can see we've got that trigger component.

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‫We can now add that in.

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‫We can remove our trigger area that we've set up previously.

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‫Just go ahead and delete that and check yet we want to delete it.

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‫It's going to basically invalidate this event that we created and we can check that the collisions are

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‫set up as we want on the trigger if we're going to have a look.

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‫Yet, it's set to overlap all dynamic and to generate overlap events.

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‫And finally, what we need to replace is this event here where we're going to select our trigger right

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‫click and go to unfurl the add event for trigger collision and add on on component begin overlap.

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‫That's what we were using before.

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‫Hook up the active pin and hook up the execution pin to head over to the dungeon level.

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‫Go and pick up the gargoyle, try and stick it in the alcove and we notice that's not working.

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‫So now we've got that trigger set up.

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‫Let's go to the viewport and you can see that actually the trigger isn't been it hasn't been made big

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‫enough.

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‫We haven't positioned it correctly.

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‫So let's go and position it in the center of the alcove and let's increase the box extent properties

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‫so that we catch whatever we've put inside this alcove area.

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‫Doesn't matter if it is a little bit bigger and gives us a safety margin and we can go into the dungeon,

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‫hit play and then step into the alcove.

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‫And sure enough, it detects that the BP player has walked in to that alcove.

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‫Great stuff.

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‫In this lecture, we've learned all about object types and object type responses, and we've used that

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‫to set up this trigger component.

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‫I'll see you in the next lecture.