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In this lecture, I'm going to be adding a second game object.

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And also we're going to be playing around with colliders and rigid bodies so objects can bump into each

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other and use the unity physics system to apply force to one another.

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So let's jump in and get started.

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Let's create ourselves something to bump into.

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So a little micro challenge for you here.

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Add a new sprite into our scene, which is a square or a circle.

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Okay.

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So over in our hierarchy, right click to the object sprites.

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I'm going to add a circle, I think, and then gives a chance to name it.

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I'll leave it as circle for the moment.

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I'm not exactly sure what it's going to be yet.

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I'm going to click on that circle hit.

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Just move it over to the side.

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Well, here we can also play around with the scaling of it.

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So I might do that, hit R on the keyboard and just scale it up a little bit around about there.

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You know what?

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I'm just going to type in to tab two.

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Tab two.

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When I say tab, I'm not typing tab, I'm just hitting tab to move to the next cell so that I can type

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in 2 to 2.

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There we go.

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We've got a two sized circle to bump into.

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I'm also going to change the color from within Sprite Renderer.

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You see color as a field.

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Click on the white space in there and change the color circle thing around the outside and then circle

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thing on the inside.

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It's kind of a yellowy orange color.

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There we go.

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So I'm going to click on play.

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We'll see what behavior we've got here at the moment.

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If I turn my vehicle towards the circle, drive over it or towards it, I just kind of drive past it.

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Nothing happens.

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The circle doesn't move.

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There's no bumping into going on here.

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So what do we need to do to get these things to bump?

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At the moment, all we've got is a Sprite renderer as the component on these game objects that says

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it looks a certain way.

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It's an image.

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Basically what we need to do is add to things.

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One of the things needs to go on both of these objects and the other thing needs to go and only one

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object.

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Okay, so what are these two things?

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First of all, we need to add colliders.

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So we go on to our player, click on our player, then find down the bottom in the inspector, add component.

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I'm going to search for Collider and we've got a whole bunch of options in here.

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Now, pay close attention to the fact that some of them say 2D and some of them don't say 2D.

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The ones that don't say 2D is when we're working with a three dimensional object.

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In other words, something that's not a Sprite.

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But when we're working with Sprite, as we are here, we want to be adding things that say 2D down the

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end.

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So what have I got here?

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Well, it's a capsule, so I'm going to look for a capsule.

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Collider two d click on that and then scroll right in.

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So you can see this.

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You can see we've got our capsule Collider 2D component.

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And what I'll do just for a moment is to turn off my Sprite renderer so that we don't have our image

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anymore.

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And you can see we've got this green line around the outside.

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Now, the player never sees the green line, but Unity knows that this green line is collision.

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It's an invisible force field that we can have things touch.

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And when they touch, we can say what the behavior will be.

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For example, they they bump off and go in a different direction or they can't pass through.

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So this is when we have a collider.

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We're also going to talk about triggers in the next lecture.

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That's something slightly different where you say some things can pass through this collision area,

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but when it does, we want to send a message.

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We want to know that it passed through it.

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You know, you've you've entered the force field and something happens or you've exited the force field

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or you're still inside the force field.

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So there's a lot of things we can do in relation to this collision.

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So I'll turn Sprite Renderer back on and then we'll jump over to our circle and we'll do the same thing.

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So little micro challenge for you again.

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Pause the video and add the appropriate sort of collider to your circle or to your square.

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If you added a square instead of a circle.

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Okay.

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So we click on Circle Add component.

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My search that I put in before is still there.

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So.

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Collider And because it's a circle, I'm going to add a circle collider to DX.

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If you added a square, then you would add a box collider to DX.

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And once again it should conform nicely to the shape of the object that we have in there, which is

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really handy.

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So you can see there we go, we've got our collision.

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Okay, so we have collision now on the outside of our objects.

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That means that unity knows, okay, what is going to bump into what.

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But there's one last step we need to do, and that is to add to at least one of these objects needs

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a rigid body.

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What is a rigid body?

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A rigid body is a way of saying this thing has substance.

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And it's the thing that the unity physics engine understands that it's going to move around and it's

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going to be able to bump into and collide and have physics interactions.

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So let's scroll down, we'll click on our player, scroll down to add component and we'll search for

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rigid body, fine rigid body 2D and add that this now says the player.

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Our cruising MC drive can interact with things using the physics system in unity and if we click on

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play, we'll see some behavior here.

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That's quite interesting.

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Our object now just automatically drops off the screen.

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Why is that?

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Well, that's because we've got gravity on.

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So if we set gravity to zero, that means that this object is not going to have any gravity applied

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to it and it's not going to drop off the screen.

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Why would we want gravity?

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Well, if we're making a side scrolling platform, we want to be able to jump and drop and jump and

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drop.

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And gravity is quite useful and quite important.

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But for us, we're making a top down driving game and there's no gravity that we can see.

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So now when I click on play, we see it doesn't go anywhere.

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And if I drive my vehicle, drive, drive, drive and bump, it bounces into this and kind of gets flung

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out of the way.

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It's not actually moving the circle.

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We'll get to that in a second.

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But I can actually have this work with the collision.

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But it's a bit odd because I bounce into this thing and it's just staying there and not moving.

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That could be valid if you've got, say, a car and then you've got like a street post or a building

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or something that you don't want to have.

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Move like a car is not going to go and move a building.

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The building is going to stand there and say, No, you didn't hurt me at all.

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But what if we wanted to move this object?

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When we bumped into it, we wanted to have it respond a little bit.

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Well, this is a little micro challenge for you.

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Again, what can you add to our circle so that when the car bumps into it, it moves?

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We can add a rigid body to this object to the circle.

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So add component once again rigid body to and what do we need to do?

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First, we need to change the gravity scale to zero.

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That's important so it doesn't go dropping off the screen.

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Now I'm going to click on play, turn my vehicle around and there's a little bit of a reaction.

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It's moving a little bit when we bump into it.

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It's not going flying off the screen and that's all fine.

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But I'm finding it a little bit difficult to kind of push the object because I keep sliding off because

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we've got this precise collision on the front of our objects, all very sliding, if you will.

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It's not hitting it tightly.

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What you could do, it's going to click play is click on our player, and then I'm just going to roll

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up a lot of these components.

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So if you click on the little arrow triangle thing here, I'm going to roll these up, roll out the

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Sprite render.

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It's still there.

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It's just I'm not seeing all the details.

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It's a way of hiding it and making your inspector more clean and tidy.

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So roll up all of these.

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Roll up all of these.

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There we go.

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It's a little bit tidier.

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I can see what I've got.

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And the Capsule Collider I'm going to click the little checkbox that says, Don't use this when we play

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the game.

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We're not using this anymore.

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It's still there, but we're just not using it.

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I'm going to add a component which will be a collider, see a box collider to DX.

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Now, when I look at my player, you can see that it's more of a straight edge at the front.

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So when I click on play, drive over to my circle, it's going to act a little bit more like a a thing

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that can push a bit more of a bulldozer, if you will.

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It's not going to give a very good effect when I do that.

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Like you can see it's going to look odd for the player.

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So I'm using this a little bit sparingly just for you and I now to see that that is another way that

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we could push a thing.

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Instead of having this capsule random thing at the front, we can have it as a square collider and also

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showing you that you could change the collider.

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Now what I could do is for my capsule collider, I could right click and remove component and we've

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deleted that.

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That's not there anymore.

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I've just got this box collider on my player, so it's pretty easy to add and remove colliders as your

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heart desires.

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So just to recap, we've added colliders to our to game objects so that they have the ability to understand

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when they're connected and touching and bumping into things.

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And we've also added rigid bodies to both of them so that they both have the ability to respond to our

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physics system.

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They can be moved around, they can interact, they can bump and all those kind of good things.

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So there we go.

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A quick introduction to colliders and rigid bodies.