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In this lecture, we're taking on a meatier challenge where we're going to have particles that play

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when the character is touching the ground and turn off when the player is in the air.

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So let's get started.

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I'll start by showing you a new concept, and then I'm going to give you a nice, big, meaty challenge

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that brings together a lot of the stuff we've been talking about in this section.

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So you don't need to follow along with adding these things.

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I'm just showing it to illustrate, we've got two sprites, one on the left, one on the right, and

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each of them has a box collider on them.

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So if I turn off that sprite renderer.

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Yeah, you can see there's the box collider on the right one and the left one has the same.

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Now, what we know already is that when this one or when that one moves and goes bump and bumps into

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that, you can see the green line on here.

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I've left it like that.

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So you can see the green line.

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This one also has its green line, which is the collider and it goes bump.

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At that very moment we get an on collision enter event that happens that unity knows about and then

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we can use that moment to do stuff.

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We can say play a particle effect or end the level or do whatever or crash the player.

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So there's a moment bump that's on collision.

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Enter 2D we've been working through.

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There's also another thing we know is that when they are no longer touching, there's another event

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which is on collision exit.

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So it works exactly the same way.

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But one is when they touch and the other is when they stop touching.

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It's the same with trigger volumes.

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If the one that I'm wiggling here is a trigger as opposed to a collider, then as you pass through it

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you'll say that's an on trigger enter.

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And as you finally leave it just there, you'll get an on trigger exit event.

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And we can use that to say, okay, when is Barre the snowboarder?

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I'm just going to delete these guys don't need them anymore.

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Thanks very much.

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When is Barre, the snowboarder, touching the ground?

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That's when his collider is touching with the ground.

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Collider We know at the very moment that happens on trigger enter and then if Barre gets some sweet

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air off one of the jumps, then we get an on collision exit moment.

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So there's a little bit of theory here is the meaty challenge, I promise.

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First of all, I'd like you to create a new script called Dust Trail.

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Okay?

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So we're going to put all of our logic in this new script, and then I want you to make particles that

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can be scattered along behind the player.

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So just a little simple particle system doesn't need to be super fancy.

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And then here's the cool thing only play the particles when the player is touching the ground.

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And this is the main meat of the challenge.

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And if that's enough for you, if you're like, Yeah, I got this, Rick, no worries, then pause the

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video.

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Take that on if you'd like a couple of hints.

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Here are some hints for you consider using on collision into 2D and on Collision Exit 2D.

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The theory that I was just telling you about, I was telling it to you for a reason.

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It wasn't just random pondering from an old man for collision events, for entering and exiting.

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We can use other game object tag to find out what it is that we're colliding with now.

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I think in the past when we were bumping into triggers, we only used other tag.

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But if it's a collision event because we're getting information about the game object, that's what

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other is all about.

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Other game objects tag might be what you need to use and then consider using particle system stock.

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We've used particle system play, so I'm pretty sure you can figure out what particle system stop is

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because I know you're a clever cookie.

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So there's our challenge.

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It's a nice, meaty one.

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Give it your best shot.

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See you back here when you're done.

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Okay.

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So I'm going to make a particle system really quickly.

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Might look a bit ugly, but click on Barry Right Click Effects Particle System.

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I rename the particle system to be, say, dust particles.

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I know they're not technically dust, but kind of the thing we're doing is pushing dust behind us.

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Kind of snow, I guess.

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But we'll call it dust, pop it in the back of where we want to come out.

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And I'm just going to change the duration down to something quite small.

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So point one, leave on looping.

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That's fine because we want it to play, play, play, play until we tell it to stop, start lifetime.

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They're going a little bit too far at the moment.

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We'll put the Lifetime down to 0.5.

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I'll do some variation later on, but for now we're just getting the macro amount start speed.

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I think that's fine as well because I'll be moving away.

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We want them to be kind of sticking around in the world emission.

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I'm going to increase this to say 50.

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I'm going to go find my renderer down the bottom, change the material, click on the little selector

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to the square thingy.

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That's good.

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They're now too big.

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So I'll reduce the size of this from one down to, say, 0.2.

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Okay, so far, so good.

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Now I'm going to change the simulation space from local to world.

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So that means as we're cruising along, let me see if I can just simulate this for you here.

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As we're cruising along, we want them to stay where we leave them in the world.

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We don't want them to follow along with Barry.

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If I was to have them on local as I move this around, you can see the entire particle system moves

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around with me.

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So I want to leave that in world space.

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Let's click on play.

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Just see if it's generally in the ballpark.

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I don't want to finesse this too much at the moment because I want to get into the code, but let's

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see so you can actually see it.

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Okay.

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Yeah.

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So I mean, there's little particles flying along behind as we cruise along looks okay.

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I'm going to change it.

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So instead of it being in a emitted in a circle like this, let's change it the shape.

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So change the shape to be a cone, I think.

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And you can see it doesn't quite look like a cone.

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Click on to DH.

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You can see the cone is pointing into the screen into the Z or Z axis.

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So if we change the the Y, yep.

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There we go.

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Now we can have it pointing backwards.

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So I'm just going to do this at -90, you know, decrease the initial start point of it.

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That would be the radius.

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Drop that down a little bit, just kick it up a bit and we'll see how this is feeling.

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Okay.

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Not too bad.

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I'm just going to change one last thing and then move on.

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I'm going to change the start.

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Speed down to say two.

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There we go.

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Some little dust particles.

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Good enough for now.

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We can finesse that a bit more later on.

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But we've got something and it's called dust particles and it's sitting on Barry.

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Next thing I want to do is to create my script.

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So create C sharp and we'll call this dust trail.

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You know, first of all, what I'll do is add dust trail where I want it to be added.

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So I'm going to add dust trail as a script on Barry.

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So I will scroll down and just drag dust trail onto Barry.

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You might be saying, why not just put all of these things in the player controller?

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Rick We could just shove all of our code in there.

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You could do that.

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But then it becomes a big old mess every time you go into the player controller script.

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If you've got four or five or six or seven different things that it's doing, you're like, Where do

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I find it?

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What's what's doing what?

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How does it work?

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So if you've got these things as separate scripts, once you've set up the dust trail, it doesn't need

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to get in the way anymore if you're doing work in the player, controller and so on.

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So this is part of good coding practice is for each class or each script.

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Try to have it, do just one thing, have one purpose to it.

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Back to dust trail.

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Now first thing I want to do is point to or get a reference for our particles.

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So I'm going to serialize field and this will be particle system and the particle system I'm going to

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call dust particles.

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Now, pretty sure I'm not going to use start or update, so we'll delete those and I'm going to create

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myself an on collision enter to DH just remove the private tidy up the formatting a little bit.

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And you know, while I'm here, I'll also add my on collision exit to DX.

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So we've got our shape all ready and raring.

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I'm also going to jump over into my world, click on my level, sprite shape and tag that as ground.

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It's already tagged as ground.

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Oh, look at that.

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We didn't need to have that as a clue that was already done.

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So yeah, for us, I like looking at the visuals when I'm trying to figure out what the code is going

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to do if the player is touching the ground play particles, if the player is not touching the ground,

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don't play particles.

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So we want to make sure, first of all, that we're touching the ground.

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So if other remember we get the information about the other thing that we're touching are the dot game

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object tag equals equals and then we want to have ground.

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Make sure we spell that correctly.

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Then what do we want to do?

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We want to find our dust particles.

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So dust particles and we want to play them.

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Man There we go.

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Parentheses, semicolon.

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If we're touching the ground play and then if we exit, if we are not touching the ground.

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So if other game object tag equals equals ground.

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So in other words, if we've just gone and exited the ground, then what do we want to do?

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Dust particles, dot stop and let's save that up and see if by some miracle I haven't forgotten a step.

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What we do need to do is find Barry.

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We've got our dust script, we've got our particle system.

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We want to grab our dust particles, drag that over there.

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So it's very clear this is what we want to be popping out behind us.

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Make my screen a little bit bigger so we see what's going on here.

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If we're touching the ground, do we have particles?

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Okay, the particles started before we landed.

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We might want to look at that.

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And then we get some sweet air, but no particles whatsoever.

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Get some speed on that.

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Awesome.

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So they're turning on and off based upon whether we're touching the ground just with a little bit of

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simple logic there.

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So hopefully you went okay with that challenge.

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Let's do one last thing here where I'm going to click on the dust particles and we just need to turn

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off the plate on a week.

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We only want to have them play when we start touching the ground.

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Let's have a look.

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Touching the ground.

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Touching the ground.

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Okay.

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So if you wanted to, you could go and finesse your particles a bit more.

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I might do a little bit of that off camera, but not enough that you need to worry about just with that

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finessing of it.

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So good stuff.

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I look forward to seeing you in the next lecture.