Unity Triggers / Game Tags / Layers / Prefabs

>> All right, everyone.

So this is part two of the Unity refresher.

Last class or last module, we talked about
creating scenes, I should say creating projects.

Creating scenes, importing 3D models,
adding lights, adding cameras.

We talked about creating materials in Unity.

We also talked about-- what
else did we talk about?

We talked about-- Oh, we also
talked about colliders and physics.

Okay. All right.

So, download the files for today.

You can look at the drills if you'd like to.

These drills are called Refresher Part II.

I have already added them into
my Unity Hub and loaded them.

This is exercise one.

Okay. This is my scene.

I have a red ball, okay,
and I have a yellow cube.

Okay. Now, if I put this in play
mode, not much is going to happen.

The reason why-- there we go.

Not much is going to happen and the reason
why is if I go back and I select this,

I don't have any physics
being applied to this, okay?

So it's not going to like move
or move around with gravity.

So I'm going to, just like we talked about
last class, I'm going to add physics,

which is going to be a rigid body.

Okay? If I go back, that should add physics,
which means it should fall with gravity.

Now, you'll notice it's falling
through the floor.

The reason why, and this goes back to what
we talked about, there's no collider on this.

So we're telling it to fall,
but it's not colliding.

You know, the way two objects collide in a game
system is they have to tell the program, "Hey,

these two things are knocking into each other."

The way that we can do that is
we are going to add a collider.

In this case, I'm going to
use a sphere collider, okay,

that goes around the entire
player, which is a ball.

What that should mean now is my
player should fall, hit the ground--

And it does.

Now I'm going to try to move
it, and I can't do that,

and that's because I need to add some code.

Okay. So in my scripts here, I'm going
to use this script called Player Move.

We'll talk about scripting later today.

But what I'm going to do is click
and add it to my character as such.

This allows my character to move.

I can play the game, I can move around.

What I'm going to do is hit this cube,
and I'm passing through the cube.

Okay. Why am I passing through the cube?

The answer is, well, if you click on the
cube, the cube does not have a collider on it.

So it's kind of like the same issue
that my red ball did, my player,

in that if both objects don't have
a collider, they don't collide.

So I'm going to add a collider.

I'm going to add a box collider to it.

All right.

And the results should be now that my
object or my player, which is the red ball,

should bounce off or collide
with the yellow cube.

And if I do that, boom, I'm doing that now.

Okay? Now that's great.

What I want to do though is I don't want
to get too deep into the code right now,

we'll cover that in a later video today.

But what I want to do is to-- I have this event,
okay, you guys remember events hopefully from p5

when you guys learned that in 327 and 427.

An event is something like a key press or like
a mouse press, right, so it's like, you know,

when you were writing code, it waited
for something to happen, right?

So I'm going to do this super quickly.

So if I go to p5.js, I can write some
code like this, function mouse pressed.

And what this will do is it waits for the event,

which in this case is a mouse
press and then it runs some code.

So I'm going to run this.

Nothing happens until I press
my kind and my, you know,

my mouse on my keyboard or mouse on my computer.

But then when I press it,
the code's been launched.

Okay? So what this is right here,
this is kind of the same thing.

The event here is though, not a
mouse press or a keyboard press.

Instead, what it is, it's waiting
for something to be triggered.

Okay. So the way I like to think
of it is kind of like a mouse trap.

All right.

So like I was saying-- sorry
for the pause there.

I was trying to get this slide going.

You got to think of a trigger kind of like
a mouse trap where it's like the action is,

you know, the thing coming down,
but the trigger is this, right?

The mouse steps on this and it
causes the trap to go, so to speak.

So what's happening is I
need to trigger this code.

Okay. I have some code written that says,
if-- I don't want to get too deep into this,

and we'll talk a little bit about this later.

This is a function, kind of
like the function I had here.

If I didn't close it or delete it, maybe I did.

Oops, maybe I did.

Anyway, in my example where I
was-- oh, I didn't close it.

All right.

So, this is a function, right?

And so is this.

And the function is basically saying, you
know, when this runs, you know, when--

"on trigger enter" means when a trigger
has been done, what's causing the trigger,

something to collide, colliding with
what, the other, do the following.

Okay? Which in this case is,
you know, causing this to occur.

Now, the way I'm going to get this to work,
I want that code, this line of code to work.

Now, normally it should show up in the console
here, but if I were to hit the play button--

Any day now.

Oops, there we go.

And I do this, it is colliding,
but it's not triggering,

even though it was supposed
to be a trigger code.

So what I'm going to do is the reason why
it's not working is if I go to my scene,

I need to have what's called a trigger.

Okay. What this says is if someone--
if something collides with the object,

it will trigger possibly some code.

Okay. Now the way I'm going to do that is, well,

we have this little option
here that says is trigger.

And I'm going to turn that on.

And let's hit play.

And what's going to happen
is now when I do this,

you can see I'm triggering
down here in my console.

Now, the other problem is this,
you might notice that, oops, well,

the collider is not actually
acting like a collider anymore.

I'm actually able to like run right
through this, like it, you know,

and that's not what I want either.

So the thing about this is like, well,
when you make a collider a trigger,

it no longer acts as a collider, okay?

I kind of feel like there should be a separate
component for this, but unfortunately,

at least currently, this is how it works.

So what I would say is like,
okay, I'm going to--

the way we can fix this problem is
I'm going to add another box collider.

Okay. So there's actually two box colliders,
one that's the trigger, one that's the collider.

So now one is going to stop the ball from going

through it while the other
is going to trigger the code.

And boom, okay.

So if I try to run through
this, that's not going to work.

Okay. So that's what a trigger is.

Trigger like it sounds like causes
possibly at least code to occur.

Okay? I'm going to go to
exercise, scene two here.

And I have a ball and I've actually already
added-- you know, it already has the rigid body

and the collider and I have this code
being applied to it that allows it to move.

Okay? And if I hit play--

What's going to happen is it's going to run
and it's going to hit that back wall there.

Okay? See what happened there?

And I want to write some code that if it
hits this, that's like the finish line.

I wanted to say in the console, you
would hit the finish line, right?

So I'm going to open up the code real quick,

which the one that's being applied
here is called Player Move Finish Line.

And what would happen is if I had something
like this, any time you collided with anything,

it would say you reached the finish line.

Okay. I'm going to save that.

Now, that's actually not what I want,
because like I'm going to show you why

that wouldn't necessarily
be something that we want.

Sorry, I'm waiting for my
code to save the update here.

Oops.

Uh-oh, what happened?

All right.

So the reason why I wouldn't want that to
happen is I'm going to add a cube to my scene.

Okay. Let me just make it real big.

And I'm just going to make it like black.

Okay. Let's also put-- let's say
that also has a trigger on it.

Okay. I'm just going to place it like here.

Okay. Now, there's two objects in my scene
and they both have triggers on it, right?

So if I were to run this, how does my
program know which one is the finish line?

Because they both have the trigger and then
what would happen is if I run into this--

oops, I don't know if I hit the trigger on it.

Oh, there it is.

So it's accidentally not,
you know, doing it correct.

Okay. Because the problem is
it's like the game can't--

or the game engine can't tell the
difference between this and this

because they all have triggers on it, right?

And all that my code basically says
is if you collide with something else

and then it has a trigger on
it, then you run this code.

So what I need to do instead is we
need to make it a little more precise.

And the way that-- an easy way to do that is
we can work with something called a game tag.

What a game tag is a game-- sorry about that.

Game tag allows you to organize elements
in your scene for coding purposes.

Okay. So what I'm going to do is if you
want to add a game tag, come up here,

and actually normally there will be some
already built into the scene, usually we'll have

like respawn and camera and
player, and stuff like that.

If you want to add one, I'm going
to go to where it says "add tag",

and I've already actually added a few.

I'm going to hit the plus sign here and
I'm going to add one that says-- oops.

Let me delete that.

Let me do it again.

And I'm going to call this finish
line, all lowercase, no spaces.

Okay. Now what I'm going to do is I'm
going to click on this and I'm going to set

that to that new finish line tag.

Okay. And then if I come into
here, what's actually happening,

hopefully, you guys remember if statements.

Remember in programming, if means, if whatever
it evaluates as true, then do the following.

Okay. So what this is saying basically is if
the object you collide with has a game tag

of the finish line, then do this.

So in other words, the finish line code,
you've reached the finish line will only run if

and only if it collides something--

collides with something that has a
game tag, a finish line applied to it.

So, because this one has that trigger,
but not the tag, it won't do that.

So let's just try that out.

If I hit the object here.

Oops. Oops.

I think I didn't turn on the trigger.

Yeah, this has to be a trigger.

Let's try that one more time.

Okay. See how that worked.

Now, I would actually fly
through it because once again,

because this is a trigger it
no longer acts as a collider.

So I'm going to add a collider to it.

Another thing that's kind of fun
is you technically don't even have

to have this be visible for the trigger to work.

You can turn off what's called
the mesh renderer.

The mesh render is what-- the mesh is the
visual part that the light bounces off of.

So if you turn it off, it
actually will make it invisible.

But the object is still there.

So what I'm going to do now, you can see
how we no longer see the finish line, right?

And then I'm going to go forward like this.

And you can see I'm hitting that wall there and
it's triggering even though we can't see it.

Okay? So game tags are useful.

We can use them to our advantage.

I would recommend that you-- you
know, the reason why you might want

to do it is maybe you want to
make a game tag for like enemy

and every time your character
hits an enemy, something happens

or every time your character
hits a tree, something happens,

or maybe every time your character
picks up an apple or whatever it is,

you can use game tags to kind of work with that.

Okay? Another thing we can
do-- so I have this scene here.

And I already have this, you know, here's my
player and the player has spheres, you know,

it has a collider on it, it has gravity
applied, and it has a script being applied.

All of the elements here have colliders on them.

Okay. So if I were to play this game or put
this into, you know-- what should happen is--

Oops.

Oops. Sorry.

Give me one second.

Let's try that again.

I hadn't set up my file correctly.

Yours should be set up correctly though.

So what should happen here is you can see

that I'm bouncing off all of
these objects here, right?

Okay. Let's just say for the sake of
argument, I want to have these objects here,

but let's just say for the sake of
argument, I don't want to have--

you know, I don't want the sphere
to interact with the cubes.

Let's just say for some reason,
I'm allowed to pass

through those, but not through other objects.

Okay? So, and maybe other objects
might interact with the cubes.

So I don't want to just make it
from everyone, just my player.

What I can do, another way to
organize this is you can actually work

with something called layers.

Okay? What you can do is you
can organize things into layers,

and then you can actually use those layers

to tell the program what is
allowed to interact with what.

Okay. So, I'm going to add a layer here.

And when I do that, you're going
to see I get things like these.

And what I'm going to do is I'm going to type
in-- I'm going to make a layer called Player

and I'm going to make a layer called Squares
and I'm going to make a layer called Spikes.

Okay. So, I've made these
layers, I'm going to close this.

And then what I'm going to do is I'm going
to put the player into the Player layer.

I'm going to put the cubes into
the cube or the Square layer.

I guess I should have called
it cubes, but whatever.

And I'm going to put the spikes
into the Spikes layer, okay?

Now by default that, you know, they are
organized, that doesn't really do a lot.

You couldn't turn off everything in one
layer if you really wanted to do that.

There are ways of turning
off objects within a layer,

but that's not what I really
want to do right now.

But if I hit play, nothing's
going to happen yet.

So, give me a second.

All right.

So see how I don't-- see how I'm not hitting
those objects, but I am hitting those.

Now-- actually, once again.

All right.

So, you can see that I did put them in layers,
but I'm still bumping in the things, right?

I don't want my player to hit these
objects, anything that's in either

of the Spikes or the Squares layer.

Okay? So what I can actually do is I'm going
to go to the project settings as a whole.

Remember, this is where we play
it around with the gravity.

I'm going to go under physics.

And under physics, this is where gravity was.

There's also this thing here
called Layer Collision Matrix.

And it might seem a little confusing.

But what it's doing is it's basically saying
what layers interact with what other layers.

Okay. The reason why doing this can help
is the more that your computer has to think

about all the things going on in your world,
the slower your world is going to run.

If your game doesn't have to worry
if two objects are colliding or not,

or anything from one layer is going to
collide with anything from another layer,

it makes the job of the game a little easier
and therefore it's going to run a little faster.

So the only thing I'm going to
worry about is here is this player.

See how player is set to Spikes,
Squares, UI, blah, blah, blah, blah.

What this is saying is, does the
player or anything on the Player layer,

which in this case is my red ball, is it going
to collide with things on the spike, square,

UI, water, player, and then default?

Okay. I don't want the player to
interact with the Spike layer.

And I don't want it to interact
with the Squares layer.

Okay. It will interact with
all of the other layers here.

Okay. So that means that it should interact
with my orange rings because although--

the reason why I should collide
with them is they're set

to the default layer, not
to one of these layers.

And so far, my Player layer should
be able to collide with this,

this, this, this, and this, and this.

Okay. So let's try that again.

Now, I'm going to go into game mode here.

And what's going to happen is you can see
I'm not going to hit any of those objects

but I will bounce off of these
because those were in default.

Okay. Now if I decided later on I didn't
want my player to interact with these.

Let's take the rings and put
them onto the Squares layer.

I think both of them got that.

No, let's send them both to Square.

Now, what should happen is my player-- or my
character shouldn't interact with those either

because it doesn't interact with
anything on the Squares layer.

All right.

See that, see how I passed right through that.

Okay. The last thing I'm going to talk
about, let's kind of put everything together.

Okay.

All right.

I have this player.

And if I click on this, it
already has the, you know,

rigid body applied and it
has this script applied.

Okay. And I'm going to run
the script real quick.

And the script essentially--

It sets up a variable.

Okay. Hopefully, you guys remember
variables from like p5 and all that.

And what it basically says is that
if you collide with another object

and that object has a game tag of ring, turn
off the other object, ring equals ring plus one.

So, you know, you have a variable
called ring, it was set to zero,

then it's going to be one, then two, then three.

Okay. And then it's going to say,
you have collected a ring, you know,

this is going to print the console.

So let's try this.

I have this ring right here and it
actually already has a collider applied

to it and it has a trigger.

Okay? What I'm going to do is I'm
going to create a game tag called Ring.

I keep doing that.

Let's do it again.

Plus sign, ring, okay.

And then I'm going to select
this and set this to ring.

And what should happen is when I-- you
know, when my character rolls, it should--

make that disappear.

And then I get a little message.

Now that's one ring, right?

Now, what if I wanted to
add multiple rings to this?

I could-- what I could do is I could add another
object, add another material, add another box,

the lighter, you know, do this, add,
set, you know, that that's a lot of work.

Okay? There's another way we can
kind of save ourselves a little bit

of time and it's called a prefab.

Okay? Prefab is short for prefabrication.

And what it means is that you can take any
object in Unity and make it kind of like sort

of like a finished model and you can
duplicate that object really quickly.

Okay. So what I'm going to
do is I want to take--

I'm going to get rid of this object,
which is the second ring here.

I'm just going to delete it.

And what I'm going to do to make this a
prefab, I already have a menu called pre--

or sorry, a folder called prefab, it doesn't--

you don't have to have this,
but I just think it's easier.

And what I'm going to do is literally drag it
into this folder, this project folder here.

Okay. And when I do that,
it's going to make a prefab.

Okay. You can tell it's a prefab because
if you look down here, it says ring.prefab.

Okay. This is showing you what that ring has.

So it has a yellow material applied to it.

It has a box collider.

It has a trigger.

It has a tag of ring.

Okay. And it tells you who's the
original parent, which is ring.

What I'm going to do is from this prefab,

I'm actually just going to
add a bunch of rings here.

So I'm just like clicking and
dragging and dragging this in.

And then I'm just going to
kind of rotate these--

as such. Maybe I'll put some back here.

Okay. So all of these rings
I've added to my scene,

they're all a prefab, they're
all a copy of this one.

Okay. And if I click on all of them, you'll
notice all of them have the same thing.

They have a box collider with the trigger,
and they have the tag of ring, box collider,

trigger, game tag a ring, box
collider, trigger, game tag a ring,

so on and so on and so on and so on.

Okay, I'm going to go and hit-- let's hit play.

All right.

And boom, boom, boom, boom, boom, boom, boom.

Okay. Now what's nice about prefabs are
if you were to ever change a prefab,

it would actually edit all of your copies.

So for instance, an easy
way to do this is I'm going

to take this prefab and I'm going to edit it.

I'm going to double-click, one, two.

And when you do that, you kind of get this kind
of blue, kind of, I call it the nether world,

the nether world where it's like,
it just kind of exists on its own.

And I can make any changes I want,

and any changes I make are going
to affect all of the copies.

So for instance, maybe I'm going to
change the material from yellow to red.

I'm just going to drag the red material
and you can see that they're updated.

Okay. Maybe I'm going to take
this model and, you know, maybe--

I don't think I can edit it from here, but
I'm going to use one of the existing ones.

So I'm actually going to switch
out the mesh for another mesh.

Maybe not.

I'm going to use a capsule.

So I'm using one of the existing meshes here.

All right.

And then I'm going to get out of this
by hitting this little back button.

And when I do that, see how
everything automatically changed.

So it's like I was able to swap out
all, not just the color but models.

I could have added or subtracted code or
anything I wanted to do, I could have done that.

It's a little confusing now.

So maybe I'll make this the yellow item.

And I'm going to hit Play.

And there you go.

All right.

So hopefully, you see why prefabs are helpful.

It's really good when you have big, more
complicated worlds to use prefabs so that

if you need to make changes,
you can kind of quickly do that.

Okay. In the next video, I'm going to
talk about programming, okay, using C#.