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In this lecture we're looking at triggers and using on trigger enter so that when the player crosses

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over a trigger volume, it will print something to the console.

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Let's get started.

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Okay, let's start this process by adding another game object that we can use as our trigger.

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So I want you to pause a video and add a box or something rectangular that we can use as a trigger.

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Okay.

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So in the hierarchy, right click to the object physics and we will add a square and square.

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We will move a little bit above or I'll move a little bit above and I'm going to stretch it a little

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bit as well.

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Just hit R and stretch it a little bit that way, change the color so we differentiate it.

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So clicking on my inspector, you can see that I've closed some things in here so it remembers.

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I wanted it closed.

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I'm going to open that up again.

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The Sprite renderer, click on the white area.

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Change this to a pink I think for our trigger.

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What do you think the next step in the process is?

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What do we need to add to this thing to know when we've passed through it, over it, around it, we

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need to add a collider.

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What sort of collider need to add a box collider to DH?

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That box collider to DS, you can see, has taken the exact shape of our object, which is great.

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Now let's see what happens when we drive our vehicle towards that new thing we've added.

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If I can drive correctly and we drive into it bump, okay.

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It doesn't move because there's no rigid body on it.

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That's fine.

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We don't need it to move, but we can bump into it.

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But what if I want to say this is like a start or finish line or this is some sort of pickup I want

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to drive over or some sort of indicator that says that the player passed from one zone to another.

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I don't want to bounce into it.

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I want to drive through it, but I still want to know when we've driven through it.

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There's one really simple thing if we've clicked on our square just here within our collider, you see

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is trigger.

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By clicking on that, we've now said that we want this collider to be a trigger sort of collider.

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Normally I wouldn't call it a trigger collider, I just call it a trigger.

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But you can see we've got a collider and we've said that collider is a trigger.

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Now when I click on play, I'm going to drive my car and my car is going to pass right over or through

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and not bumping into it, not getting stopped by it.

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Now, why is it going underneath?

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While we talked about this in the first section of the course, it's because of our layer order.

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This square is at Layer Order zero and our player is also at Layer Order zero.

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So it's a little bit random.

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Which one is going to be on top?

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Which one's going to be below?

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I'd like the player to always be on top of these things, so I'm going to change the order in layer

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for the player cruising drive to ten.

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Now when we drive over this, it should drive and actually you'll see it driving over there we go over

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the object, which is cool.

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What's the next step?

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Well, we need to jump into our script, into our collision CSS script, similarly to the way we said

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on Collision Enter, we're going to use a new method which is on trigger enter 2D.

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And I'm going to give this to you as a challenge to see how well you've been paying attention.

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Print When we trigger something so you use on trigger enter to DD and debug dot log to print yet another

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witty message to the console when we trigger something.

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So there's is your challenge pause video.

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Take that on, test that it works and I'll see you back here when you're done.

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Right.

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So in our code, I'm going to give myself a couple of new lines to give some space.

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I will type in on trigger, enter, find the 2D version, and it adds in all this stuff as it did before.

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I'm just going to remove private because that's what I like to do and tidy up my curly braces.

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Now from within this area, I'm going to type debug log parentheses, quotation marks and I will say,

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what was that?

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Not very witty once again, but I've got ouch when I bump into it.

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And what was that.

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Because the player pass through something, save back over into unity, make sure we're on the console

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so we can see what's going on there.

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Click play and we'll drive over the pink area bump and it says, What was that the moment I pass into

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it?

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So you can see right about now it increases my number in terms of my count bump just about there and

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it only does it when we first touch it the whole way, passing through.

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Nothing, nothing, nothing, nothing, nothing.

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And we leave.

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There's another method which is on trigger exit.

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If you want to know when someone leaves a particular area, you can use that method.

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But I'm going to bump, touch it and then it will increase.

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The other thing you could do is you could click on your square and turn off the sprite renderer so the

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player doesn't even know there's a thing there.

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I drive through it.

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I know it's there.

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You know it's there.

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That's our little secret.

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But see how my count is still increasing because I'm driving over that area.

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So that's the way that we can also use a trigger volume in a way that the player doesn't even know.

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So there's plenty of occasions in games where we want to say, Did the player reach this point or did

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something go off screen?

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If it did, then do something to it, or did I go into a particular zone so triggers a super useful.

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And with that, my friend, you have the foundation of many games out there.

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You now know to have how to have the player go through a trigger volume and to have something happen

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in the code when that happens.

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And also for the player to bump into something and to have something happen in the code when that happens.

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So that really is the foundation of so many things that we do in our games, the triggers and colliders.

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So that's all for this lecture.

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I will see you in the next one.