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COLTON OGDEN: All right.

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Good evening, everybody.

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Welcome back to GD50.

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This is lecture six.

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And today we're going to be
venturing out of the 8-bit world

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and back into a more
modern era of gaming.

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We're talking about Angry Birds today.

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I have pretty fond memories
of Angry Birds, actually.

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It was the first mobile
game that I remember

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playing where I realized that mobile was
actually a viable platform for gaming.

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I played it, I think, back in 2009,
was when it was first released.

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And I really enjoyed it.

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It has a very simple formula.

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The goal, if you're
unfamiliar, is you have

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birds that you control by a sling
shot on the left side of the screen.

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And then these pigs that
have stolen your eggs,

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you're trying to destroy
them or kill them

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by knocking down their fortresses made
out of various materials, wood, glass,

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metal.

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And you get a few different bird types.

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But the gist of it is, basically, just
sling shot a bird into some structure,

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knock it down.

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And the whole entire
underlying mechanism

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for how things work is
via a physics engine,

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which we'll talk about today in
lecture, called Box2D Probably

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the most ubiquitous 2D physics engine.

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But that's the overall
structure of the game.

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It's literally just throwing things
into structures, knocking them down.

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And then that tactile and fun game play
makes for really great mobile gaming.

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And I enjoyed it a lot back in the day.

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This is a screenshot of the first
level in the first Angry Birds, which

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most people I think have probably seen.

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This is a sample from
one of their newer games.

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As you can see, it's taken
a whole new layer here.

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There's stone and a bunch of intricately
varying structures and new creatures

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and stuff like that.

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The game has changed a lot, but
the formula has stayed the same.

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And today we'll explore the foundation
of what makes this game work.

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And the topics today,
a smaller than usual.

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But Box2D, we can consider as
being a pretty large topic.

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We'll be talking about
Box2D, which is the physics

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engine we'll be using today in lecture.

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And via Love2D, which has
its own wrapper for Box2D.

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And we'll also talk a little bit about
mouse input, which you haven't really

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done a lot.

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But it's very apt, especially
in the context of mobile gaming.

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Because mouse input and
touch input are synonymous.

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But first, let's get a lecture demo.

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If we have a volunteer come
up on stage to showcase

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what I've put together here.

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So let me make sure I'm in
the right directory here.

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So whenever you're ready,
go ahead and press Enter.

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So this is a little demo I put together
to demonstrate the concepts we'll

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talk about today in class.

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This is just the Start
screen, but it already

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shows Box2D representing a bunch of
these square shaped aliens, which

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we'll actually be what we're
trying to target in the game.

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But notice that they all fell
and had their own collision

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and their own physics that took place,
and I didn't have to manually code

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rotation and stuff like this.

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This is all stuff that
Box2D takes care of for us.

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And we'll see it used
to great effect soon.

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If you go ahead and just
click anywhere on the screen,

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we'll go to the main part of the game.

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So this is a very simple
representation of what Angry Birds is.

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You start on the left
side of the screen.

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You have a bird, in
this case an alien, we

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used a free art pack that
uses aliens instead of birds,

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but it's the same concept.

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You have an alien that
you can click and drag.

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So if you click it and
then drag around, you

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can see the trajectory that you'll
have when you let go of the mouse.

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So we're simulating where it's going
to go via these purple circles.

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And then the goal in Angry
Birds is to throw the bird into,

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or the alien, into the
fortress guarding the pigs,

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or in this case, square shaped aliens.

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So if you go ahead and just launch
the bird by letting go of the mouse

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you'll see.

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Oh, there we go.

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And we knocked down the.

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OK.

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What happened was we shot
the alien into the structure.

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It destroyed one of the wooden
blocks guarding the other alien.

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And then, as soon as that
happened, the top box,

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because these are all being
simulated via Box2D's physics engine,

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that other box was detected
as being unsupported.

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So it fell down, it hit the other alien.

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And we've coded it so that
when a collision occurs

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between an obstacle and our
alien of sufficient speed,

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it should kill the alien.

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Which is how it works in Angry Birds.

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So if you'll try it again.

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And this time we hit both
of those at the same time.

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So it triggered both
of those being deleted.

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But this guy is still alive.

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So after it stops moving,
which is similar to how

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it behaves in the original game, it's
going to let us try again to shoot.

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So if we try one more time.

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And then we launch and hit it, we
kill it and then we get a victory.

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So that's the overall underlying
foundation for what Angry Birds is.

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Obviously we're using a
very simple representation.

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It doesn't have a lot of the
frill that Angry Birds does.

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But we could easily build upon
this and create a fully fleshed out

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game very similar to Angry Birds.

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So thanks, Steven.

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I appreciate the demonstration.

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So that's our goal today.

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We'll be talking about how to construct
a very basic but functional simulation

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of what Angry Birds is at its core.

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Which is just flinging things
into obstacles, destroying them,

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and ultimately destroying the
things that they're protecting,

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the aliens, the pigs that
are in the base game.

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So here's a shot of what the different
sprite sheets we're going to be using

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are.

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There's a really great sprite sheet
that I got off of Open Game Art.

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Kenny is the artist.

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He makes a lot of great art.

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If you notice, it's very
similar looking to the art

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that we use in the Mario lecture.

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Actually, it's the same artist.

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So if you're ever looking for assets,
he's got a ton of awesome assets

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on open game art.

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So we have a set of aliens,
square and round shaped.

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I decided just arbitrarily we made
the round shaped aliens the birds.

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So we shoot those into
the structures that are

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protecting the square shaped aliens.

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The square shape aliens will
be the bad guys in this case.

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And then we have another sprite sheet
down here below on the left side.

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Which just, I used the tile here
just to make a ground element.

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The rest of these you could easily
include in the game if you wanted to,

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but we're only using the ground here.

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And then notice here, we
have this large sprite sheet

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which has a bunch of different
shapes and sizes of materials.

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The whole sprite sheet comes with metal
and explosive and glass sheets as well.

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But just for simplicity
we only use the wood here.

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But notice that we have
entirely whole pieces

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and then we have pieces
that are partially destroyed

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and then pieces that are hollow.

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You could easily model all of
these in your game and use them.

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But we only decided to use
just a couple of these,

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which was just the horizontal
and the vertical ones that

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are completely whole.

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These, unfortunately, don't have
quite the same systematic layout

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as the sprites that we used before.

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They're not laid out in
a grid evenly spaced.

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So in this case, in util
dot Lua, I ended up hard

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coding the different XY
width and height quads

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for each of these, which is what
you have to do in a situation

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where you're interacting
not with tiles per se,

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but with more organic shaped objects.

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So it can take a little
more time to end up

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constructing all of the
quads for your objects

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when you have a sprite sheet like this.

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But, fortunately, you
only have to do it once.

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Here's a few useful links before we get
started in talking about what Box2D is

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and how to use it, and basically
how it's called love dot

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physics, effectively, in love2D.

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The first two links are
documentation for love 2D,

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what the functions and objects
are that we'll be talking about.

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And a simple tutorial that
talks about how to make a ball

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bounce in love 2D using Box2D.

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The third is a great
resource that I used actually

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to learn most of what I
know about Box2D, especially

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in the context of this lecture.

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So it talks about a lot
of different concepts.

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It talks about all the things
that we'll be talking about.

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And then it goes into a
lot more detail about how

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you can go about constructing a lot of
really cool, crazy things like tanks

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and pulleys and a whole
bunch of different things

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that are worth looking into if you're
looking into potentially making

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a physics based game.

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Obviously we won't be going into
things of that complexity here.

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But you could easily do it with Box2D.

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It makes it very, very possible.

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So the very first thing
that we should talk

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about when we want to construct
a game, or simulation,

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or whatever we want to
do, with Box2D is we

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need some sort of system that will
actually perform the simulation for us.

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And the fundamental core of what a Box2D
app or game is, the core is the world

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object.

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So there is a world that you can
think of as sort of being your world,

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but what it effectively is is a machine
that simulates all of the pieces

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that you've told it interact
with each other in Box2D.

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So Box2D has a set of objects
called fixtures and bodies.

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Those perform the physical interactions.

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And it's up to the world
to update all of those

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and apply the relevant forces
and physics calculations

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that resolve collisions
and do all sorts of things.

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All of the things that
Box2D does for us, the world

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takes care of this for us.

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So we don't have to manually go
through and update every single object

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with its velocity that we've done
before and check for collisions.

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The world does this for
us, and resolves them

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based on how we tell it to resolve them.

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And the world also possesses,
like an actual world

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would, gravity on the x and y-axis.

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In this case, we have gravity
applied on the y-axis going down,

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so it's a positive value.

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We set it to 300 in this distro, but
you can set it to whatever you want.

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Setting a lower gravity
would have the effect

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of making it feel like we're
on the moon or something.

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Making it feel like we're
on a different planet.

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So that's what the world is.

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The world simulates everything.

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And we'll go through
just a few terms here

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before we look at some source code.

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But there's a few terms that we need
to understand before we can really

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understand what Box2D is doing.

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And this is the function that we
use to create a new world in love2D.

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Very simple, love dot
physics dot new world.

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And this love dot physics
is just a name space that

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encapsulates all of the Box2D functions
and objects that love2D has access to.

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So anything that you see in
love dot physics is effectively

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a wrapper for Box2D.

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And to clarify about Box2D, Box2D is
just a library that's written in C++

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that you can plug-in pretty
much anywhere you want to.

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Unity uses it and, actually,
most 2D game engines

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that I've ever seen including Live GDX,
for example, which is a very large Java

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2D game framework uses Box2D.

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You can use it anywhere.

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In this case we're using
love2D's own wrapper for it.

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So the people that created
love 2D, they took Box2D

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and then they just put
a bunch of Lua functions

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around them, around all
the objects and functions

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to make it possible to
use it in the same style

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that we use the rest of the framework.

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This is how you create a new world.

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This is the first step in getting
your Box2D simulation working.

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So any questions so far as
to how we can get that going?

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OK.

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So beyond the world object, which is the
foundation, sort of sets up our stage,

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you can think of it as
our stage, we need bodies

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to actually interact with each other.

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So a body is just an abstract container.

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00:11:47,880 --> 00:11:52,650
It basically holds a
position and a velocity.

240
00:11:52,650 --> 00:11:56,190
And you attach things to it
via what are called fixtures

241
00:11:56,190 --> 00:12:00,612
that allow you to give the body a
shape, and therefore a collision box,

242
00:12:00,612 --> 00:12:02,820
and therefore allow it to
interact with other things.

243
00:12:02,820 --> 00:12:07,590
But a body is essentially all the
disparate things in your scene interact

244
00:12:07,590 --> 00:12:09,510
with each other and move around.

245
00:12:09,510 --> 00:12:14,160
And so to create a new body we just
do love dot physics dot new body.

246
00:12:14,160 --> 00:12:17,610
We pass in the world, so
therefore when we do this,

247
00:12:17,610 --> 00:12:19,950
the world has a reference
to this body now.

248
00:12:19,950 --> 00:12:22,440
And every time we call
update on our world, which

249
00:12:22,440 --> 00:12:25,230
we'll see in the source
code, it will know, OK,

250
00:12:25,230 --> 00:12:29,280
I have a reference to this body,
perform all of the relevant checks

251
00:12:29,280 --> 00:12:33,660
on the collision for that body and
all the fixtures that it contains.

252
00:12:33,660 --> 00:12:38,770
Update its position, updates
velocity, and so forth.

253
00:12:38,770 --> 00:12:41,700
And not only a world, but
it also gets an x and a y,

254
00:12:41,700 --> 00:12:45,900
which will place it in the
world on instantiation.

255
00:12:45,900 --> 00:12:48,970
The last parameter here, type.

256
00:12:48,970 --> 00:12:51,330
There are three
fundamental types of bodies

257
00:12:51,330 --> 00:12:56,130
which we'll see in love 2D,
static, dynamic, and kinematic.

258
00:12:56,130 --> 00:12:59,580
And that basically influences how
it'll interact with the other objects,

259
00:12:59,580 --> 00:13:01,810
the other bodies, in our scene.

260
00:13:01,810 --> 00:13:04,860
So we have the world, which
encapsulates everything,

261
00:13:04,860 --> 00:13:06,900
all the bodies, all the fixtures.

262
00:13:06,900 --> 00:13:10,380
And then we have the bodies, which
are the entities in our game world

263
00:13:10,380 --> 00:13:14,310
that have position and
velocity, effectively.

264
00:13:14,310 --> 00:13:18,180
The last key ingredient
here that will allow

265
00:13:18,180 --> 00:13:23,820
us to create interactions between
the bodies that we have are fixtures.

266
00:13:23,820 --> 00:13:28,680
And fixtures, all a fixture
is, is this abstract object

267
00:13:28,680 --> 00:13:31,650
that will allow you to
attach a shape to a body.

268
00:13:31,650 --> 00:13:34,740
So bodies are shapeless by
default. They don't have a shape.

269
00:13:34,740 --> 00:13:39,930
They are just a container that has
position velocity, effectively.

270
00:13:39,930 --> 00:13:42,010
But they don't interact
with anything else.

271
00:13:42,010 --> 00:13:44,260
And they don't know how to
interact with anything else

272
00:13:44,260 --> 00:13:46,290
until you give them a fixture.

273
00:13:46,290 --> 00:13:50,170
And the fixture you will
give the body and a shape.

274
00:13:50,170 --> 00:13:52,860
So for example, if you
want the bird that we

275
00:13:52,860 --> 00:13:56,715
were looking at earlier, the alien, the
round alien, we create a body for it

276
00:13:56,715 --> 00:13:59,880
in our world, which
doesn't mean anything yet.

277
00:13:59,880 --> 00:14:03,810
But we say, I'm going to
attach a fixture to that alien.

278
00:14:03,810 --> 00:14:05,760
I'm going to give it a circle shape.

279
00:14:05,760 --> 00:14:08,970
And it'll then know whenever
it performs any calculations,

280
00:14:08,970 --> 00:14:13,170
that that alien should interact
with things as if it were round.

281
00:14:13,170 --> 00:14:16,410
And therefore trigger collisions
based on a circular hitbox,

282
00:14:16,410 --> 00:14:21,180
as opposed to a rectangular or
polygonal hitbox, as we'll see.

283
00:14:21,180 --> 00:14:24,390
Fixtures, in addition
to attaching shapes

284
00:14:24,390 --> 00:14:27,300
to bodies, which will,
as said here, influence

285
00:14:27,300 --> 00:14:32,010
how they collide with other bodies,
they have density, which we'll see.

286
00:14:32,010 --> 00:14:34,110
So that things with
higher density obviously

287
00:14:34,110 --> 00:14:38,704
will fall faster, or not fall faster,
but they will influence things

288
00:14:38,704 --> 00:14:39,870
as if they have more weight.

289
00:14:39,870 --> 00:14:43,660
They will push things farther
when they collide with them.

290
00:14:43,660 --> 00:14:46,110
They also have friction
and they have restitution.

291
00:14:46,110 --> 00:14:48,120
Restitution is bounciness.

292
00:14:48,120 --> 00:14:51,810
So if something, if we had our alien,
no restitution when it hits the ground

293
00:14:51,810 --> 00:14:53,590
it'll just fall flat.

294
00:14:53,590 --> 00:14:55,410
But if we give it a
higher restitution it

295
00:14:55,410 --> 00:14:58,080
will actually bounce
when it hits the ground.

296
00:14:58,080 --> 00:15:02,380
And therefore interact with the
world a little bit differently.

297
00:15:02,380 --> 00:15:08,000
So when we want to take a fixture
and apply a shape to a body,

298
00:15:08,000 --> 00:15:09,750
we have a few different
shapes that we can

299
00:15:09,750 --> 00:15:12,930
apply to it that are given
to us by default in love 2D.

300
00:15:12,930 --> 00:15:15,340
So circle shape, rectangle
shape, edge shape.

301
00:15:15,340 --> 00:15:18,520
These are just, effectively,
how we define how

302
00:15:18,520 --> 00:15:20,680
our bodies interact with other bodies.

303
00:15:20,680 --> 00:15:24,010
How, for example, if it's
something that's circular

304
00:15:24,010 --> 00:15:26,680
it should roll when it's
moving along the ground.

305
00:15:26,680 --> 00:15:29,680
Or when it hits something
the corner obviously of it

306
00:15:29,680 --> 00:15:32,990
won't hit something because it's
rounded, as opposed to something

307
00:15:32,990 --> 00:15:36,670
that has a square hit box, it'll affect
things in a slightly different way.

308
00:15:36,670 --> 00:15:40,840
And we can define arbitrarily shaped
hit boxes, thanks to the polygon shape.

309
00:15:40,840 --> 00:15:45,560
If we want something to be shaped
like a pentagon, for example,

310
00:15:45,560 --> 00:15:47,870
and have it roll around
and behave like such,

311
00:15:47,870 --> 00:15:51,730
we can just define a polygon
via a set of vertices.

312
00:15:51,730 --> 00:15:54,820
And then affix that
to a body and it will

313
00:15:54,820 --> 00:15:57,900
behave as if it were pentagon shaped.

314
00:15:57,900 --> 00:16:00,280
And this is how you would
instantiate just as we've

315
00:16:00,280 --> 00:16:03,940
seen with love dot physics dot new
world and love dot physics dot new body,

316
00:16:03,940 --> 00:16:07,180
love dot physics dot new fixture
takes in a body and a shape,

317
00:16:07,180 --> 00:16:10,180
and will apply that shape to the body.

318
00:16:10,180 --> 00:16:14,779
And the world after that will know
exactly how to collide with things.

319
00:16:14,779 --> 00:16:16,570
And so the last thing,
the last slide we'll

320
00:16:16,570 --> 00:16:19,229
look at here before we
start looking at source code

321
00:16:19,229 --> 00:16:20,770
is what the different body types are.

322
00:16:20,770 --> 00:16:25,600
So I alluded to having three different
body types before, static, dynamic,

323
00:16:25,600 --> 00:16:26,710
and kinematic.

324
00:16:26,710 --> 00:16:32,080
So a static body will exist in our world
but not actually be affected by gravity

325
00:16:32,080 --> 00:16:34,090
or the collision of anything else.

326
00:16:34,090 --> 00:16:36,730
Things can hit it and bounce off
of it and do their own thing,

327
00:16:36,730 --> 00:16:39,790
but the static body will never
be influenced by something else.

328
00:16:39,790 --> 00:16:43,817
It exists as some sort of permanent
structure, almost like the ground.

329
00:16:43,817 --> 00:16:46,900
You don't really affect the ground by
moving into it and bouncing into it,

330
00:16:46,900 --> 00:16:49,360
unless you do it with enough force.

331
00:16:49,360 --> 00:16:55,090
But in our Box2D world, a static body
cannot be influenced by anything else.

332
00:16:55,090 --> 00:16:57,770
A dynamic body is the opposite.

333
00:16:57,770 --> 00:17:03,310
It has the full simulation of Box2D.

334
00:17:03,310 --> 00:17:06,790
Gravity affects it, things collide
into it, it will bounce off of them.

335
00:17:06,790 --> 00:17:09,010
It'll do what you would
expect a normal body to do.

336
00:17:09,010 --> 00:17:13,150
If I throw a ball in this room and it
hits the wall, it's a dynamic body.

337
00:17:13,150 --> 00:17:15,940
The walls are the static
bodies in this case.

338
00:17:15,940 --> 00:17:19,720
And then a kinematic body
is a hybrid between the two.

339
00:17:19,720 --> 00:17:24,109
It's something that can move
and can rotate and do things,

340
00:17:24,109 --> 00:17:28,400
but it's not influenced by
other objects colliding with it.

341
00:17:28,400 --> 00:17:32,860
So, for example, if I have a platform
that's just spinning indefinitely,

342
00:17:32,860 --> 00:17:36,940
but it's not being affected by gravity
and it doesn't move when I hit it,

343
00:17:36,940 --> 00:17:38,170
that's a kinematic body.

344
00:17:38,170 --> 00:17:42,400
It's still moving and it's semi-static
and it influences other things,

345
00:17:42,400 --> 00:17:43,660
but it's not purely static.

346
00:17:43,660 --> 00:17:47,197
It does have a little bit of
behavior that it can grant it.

347
00:17:47,197 --> 00:17:49,030
So let's go ahead and
look at a few examples

348
00:17:49,030 --> 00:17:53,030
now and see how this
actually looks in code.

349
00:17:53,030 --> 00:17:56,380
So I'm going to go into an example,
if you're looking in the distro,

350
00:17:56,380 --> 00:17:58,600
there is an example called static.

351
00:17:58,600 --> 00:18:02,227
So we'll take a look here and see what
a static body looks like in our scene.

352
00:18:02,227 --> 00:18:04,560
And for all of these examples
leading up to Angry Birds,

353
00:18:04,560 --> 00:18:08,320
we're just going to render everything
with shapes for simplicity.

354
00:18:08,320 --> 00:18:14,350
But this, as anti-climactic as
it is, is a full Box2D world

355
00:18:14,350 --> 00:18:17,020
with just a single static body.

356
00:18:17,020 --> 00:18:19,410
And it's just this square
here, colored white.

357
00:18:19,410 --> 00:18:21,620
The static body doesn't
move, it doesn't do anything.

358
00:18:21,620 --> 00:18:25,000
Nothing can influence
how it moves or behaves.

359
00:18:25,000 --> 00:18:27,190
But it exists in our world
as a permanent fixture.

360
00:18:27,190 --> 00:18:30,370
And if we had dynamic bodies and
we threw a dynamic body at it,

361
00:18:30,370 --> 00:18:32,770
for example, the dynamic
body would bounce off,

362
00:18:32,770 --> 00:18:34,872
the static body would
stay there permanently.

363
00:18:34,872 --> 00:18:36,580
So let's go ahead and
take a look at what

364
00:18:36,580 --> 00:18:38,200
the source code looks like for that.

365
00:18:38,200 --> 00:18:42,820
So I'm here in main dot
Lua of our static file.

366
00:18:42,820 --> 00:18:46,630
And just as we've seen before,
we needed to find a world.

367
00:18:46,630 --> 00:18:49,270
So I have a world here on line 45.

368
00:18:49,270 --> 00:18:52,960
Love dot physics dot new
world, no x-able gravity,

369
00:18:52,960 --> 00:18:57,910
but we are going to have 300 units of
positive gravity on the y-axis, which

370
00:18:57,910 --> 00:19:01,720
is going from top to bottom.

371
00:19:01,720 --> 00:19:06,460
We need a body for our square that's
in our game world, our static square.

372
00:19:06,460 --> 00:19:08,800
So we're going to go ahead
and define a new body here.

373
00:19:08,800 --> 00:19:11,251
Love dot physics dot new
body takes in the world,

374
00:19:11,251 --> 00:19:14,500
recall, because that's how our world's
going to have a reference to that body,

375
00:19:14,500 --> 00:19:18,117
doesn't know about it unless we pass
it into here, our new body constructor.

376
00:19:18,117 --> 00:19:20,950
And then I'm just going to put it
right in the middle of the screen.

377
00:19:20,950 --> 00:19:25,030
So virtual width divided by 2
and virtual height divided by 2.

378
00:19:25,030 --> 00:19:29,020
The difference between
Box2D bodies and things

379
00:19:29,020 --> 00:19:31,270
that we've drawn before
or seen before is

380
00:19:31,270 --> 00:19:34,690
that everything is defined by its center
point, as opposed to its top left.

381
00:19:34,690 --> 00:19:37,150
So I'm able to say
virtual width divided by 2

382
00:19:37,150 --> 00:19:39,270
and virtual height divided by 2 here.

383
00:19:39,270 --> 00:19:42,790
But I don't actually need to say virtual
width divided by 2 minus whatever

384
00:19:42,790 --> 00:19:44,800
the half of that square is.

385
00:19:44,800 --> 00:19:50,740
By default, the center point
is the XY of that object.

386
00:19:50,740 --> 00:19:55,600
And this last string here in the
constructor for our new body, static,

387
00:19:55,600 --> 00:19:58,810
tells the constructor that this is
going to be a static body specifically,

388
00:19:58,810 --> 00:20:02,960
not a dynamic body and
not a kinematic body.

389
00:20:02,960 --> 00:20:05,962
So we have a body and it's static,
but it doesn't have a shape,

390
00:20:05,962 --> 00:20:08,920
it doesn't really know how to interact
with anything else in our world.

391
00:20:08,920 --> 00:20:10,270
So we're going to give it a--

392
00:20:10,270 --> 00:20:12,340
we're going to create a new shape first.

393
00:20:12,340 --> 00:20:18,347
So love gives us a few functions
in the form of new X shape.

394
00:20:18,347 --> 00:20:20,930
We have new rectangle shape, new
circle shape, new edge shape,

395
00:20:20,930 --> 00:20:22,620
a few other ones.

396
00:20:22,620 --> 00:20:26,380
We're just going to create a new
rectangle of width and height of 10.

397
00:20:26,380 --> 00:20:28,420
So that's what the 10 and 10 are here.

398
00:20:28,420 --> 00:20:31,070
Then we're going to
create a new fixture.

399
00:20:31,070 --> 00:20:37,370
We're going to affix the box shape
to our body with this function.

400
00:20:37,370 --> 00:20:44,420
And then once we do that, all we have
to do is then render a polygon with fill

401
00:20:44,420 --> 00:20:48,950
and then we get the coordinates for
our-- or the vertices for our polygon

402
00:20:48,950 --> 00:20:52,190
by saying, body get world points.

403
00:20:52,190 --> 00:20:55,940
So that's a function
off of any Box2D body

404
00:20:55,940 --> 00:21:01,400
that will basically get where it is
in the world and all of its vertices.

405
00:21:01,400 --> 00:21:04,730
And then you just pass in the shape
that you want to get the points for.

406
00:21:04,730 --> 00:21:08,300
And that will end up just exploding
here into a set of vertices

407
00:21:08,300 --> 00:21:10,790
that fill up this love
dot graphics dot polygon.

408
00:21:10,790 --> 00:21:17,090
And the end result of
that is we get a square.

409
00:21:17,090 --> 00:21:21,275
And we specifically use
polygon instead of love

410
00:21:21,275 --> 00:21:24,566
dot graphics dot new rectangle
because that's what the get

411
00:21:24,566 --> 00:21:26,690
world points function explodes out to.

412
00:21:26,690 --> 00:21:32,150
It doesn't explode out to the number
of arguments that would satisfy

413
00:21:32,150 --> 00:21:35,040
love dot graphics dot rectangle.

414
00:21:35,040 --> 00:21:37,460
So not a very exciting example.

415
00:21:37,460 --> 00:21:43,110
But this is basically the foundation
of a full Box2D application.

416
00:21:43,110 --> 00:21:46,411
So any questions as to
how this works at all?

417
00:21:46,411 --> 00:21:47,036
AUDIENCE: Yeah.

418
00:21:47,036 --> 00:21:48,032
I'm wondering.

419
00:21:48,032 --> 00:21:52,514
How does it determine the
center of a abnormal shape?

420
00:21:52,514 --> 00:21:54,804
Not like a polygon, square,
rectangle, or circle.

421
00:21:54,804 --> 00:21:56,720
COLTON OGDEN: The center
of an abnormal shape.

422
00:21:56,720 --> 00:21:57,710
I'm not entirely sure.

423
00:21:57,710 --> 00:22:00,774
The circle is just--

424
00:22:00,774 --> 00:22:01,680
AUDIENCE: [INAUDIBLE]

425
00:22:01,680 --> 00:22:02,471
COLTON OGDEN: Yeah.

426
00:22:02,471 --> 00:22:04,790
I'm not entirely sure
about a polygon though.

427
00:22:04,790 --> 00:22:06,790
I haven't looked into
that into too much detail.

428
00:22:06,790 --> 00:22:08,040
I can explore that and see.

429
00:22:08,040 --> 00:22:11,320
That's something that I think Box2D is--

430
00:22:11,320 --> 00:22:14,300
the actual library implements
that and calculates that.

431
00:22:14,300 --> 00:22:18,029
Probably based upon
calculating the area of--

432
00:22:18,029 --> 00:22:20,570
and to repeat for the camera if
I didn't repeat already, it's

433
00:22:20,570 --> 00:22:25,340
how does Box2D calculate the center
point of something non-symmetrical,

434
00:22:25,340 --> 00:22:27,860
like a polygon?

435
00:22:27,860 --> 00:22:33,230
And best I can understand is that it
would do an area calculation off of it

436
00:22:33,230 --> 00:22:38,567
and figure out where all the
vertices tend towards, I guess.

437
00:22:38,567 --> 00:22:41,150
But, yeah, that's something
that's implemented in the library.

438
00:22:41,150 --> 00:22:42,170
I'm not entirely sure.

439
00:22:42,170 --> 00:22:46,469
I can look into it and see and
then I'll post in the Slack.

440
00:22:46,469 --> 00:22:48,718
AUDIENCE: It seems like
[INAUDIBLE] you did have that,

441
00:22:48,718 --> 00:22:52,940
it would be difficult to
place in a very precise spot.

442
00:22:52,940 --> 00:22:55,010
COLTON OGDEN: Yeah.

443
00:22:55,010 --> 00:22:56,810
If it were-- yeah.

444
00:22:56,810 --> 00:23:00,220
If we did have an odd shape to
get it placed in a exact spot.

445
00:23:00,220 --> 00:23:01,440
Yeah, I'm not entirely sure.

446
00:23:01,440 --> 00:23:04,450
I'd have to explore that a little bit.

447
00:23:04,450 --> 00:23:05,450
Interesting idea though.

448
00:23:05,450 --> 00:23:07,980


449
00:23:07,980 --> 00:23:13,444
But, yeah, that's essentially how
we get a Box2D world up and running.

450
00:23:13,444 --> 00:23:14,360
We have a static body.

451
00:23:14,360 --> 00:23:16,580
It's not terribly interesting.

452
00:23:16,580 --> 00:23:19,130
But with one change--

453
00:23:19,130 --> 00:23:23,150
so I have a separate example called
dynamic in the source code distro.

454
00:23:23,150 --> 00:23:26,760
But all we need to do to
really see the difference

455
00:23:26,760 --> 00:23:32,360
between a static and dynamic body is on
line 48, just change static to dynamic,

456
00:23:32,360 --> 00:23:35,660
save it, and then rerun it.

457
00:23:35,660 --> 00:23:38,300
And then we'll immediately see
that it's affected by gravity

458
00:23:38,300 --> 00:23:41,930
and it moves downwards as we've
told the world that our gravity is

459
00:23:41,930 --> 00:23:43,880
set to positive 300.

460
00:23:43,880 --> 00:23:47,000
And so that behaves how
we would expect it to.

461
00:23:47,000 --> 00:23:50,730
Now, there's nothing else in the scene
so it's not particularly interesting.

462
00:23:50,730 --> 00:23:55,220
So I've created a another
example called ground.

463
00:23:55,220 --> 00:23:58,110
So let's go ahead and look at that.

464
00:23:58,110 --> 00:24:02,970


465
00:24:02,970 --> 00:24:09,408
So if we want more interesting behavior,
what do we need to do in a nutshell?

466
00:24:09,408 --> 00:24:11,719
AUDIENCE: Have more
shapes and make a ground.

467
00:24:11,719 --> 00:24:13,760
COLTON OGDEN: Some more
shapes and make a ground.

468
00:24:13,760 --> 00:24:14,600
Exactly.

469
00:24:14,600 --> 00:24:17,330
That's a simple way we
can start to get instantly

470
00:24:17,330 --> 00:24:19,490
a sense of how powerful Box2D is.

471
00:24:19,490 --> 00:24:22,940
Just introduce more shapes that interact
with each other in different ways.

472
00:24:22,940 --> 00:24:28,540
So ground is an example that just
introduces a ground into our scene,

473
00:24:28,540 --> 00:24:33,590
so that we can see the box fall down and
actually collide with something else.

474
00:24:33,590 --> 00:24:36,480
And Love2D makes this nice and easy.

475
00:24:36,480 --> 00:24:37,190
Excuse me.

476
00:24:37,190 --> 00:24:40,640
They have a actual edge
shape that will allow us

477
00:24:40,640 --> 00:24:44,150
to basically form where the ground is.

478
00:24:44,150 --> 00:24:48,710
Anything that collides with
this-- it's effectively a line.

479
00:24:48,710 --> 00:24:52,430
But no matter how fast
anything moves in are scene,

480
00:24:52,430 --> 00:24:56,690
the body will not move past that line.

481
00:24:56,690 --> 00:25:00,100
So it's a nice, easy way of
getting a ground in our scene

482
00:25:00,100 --> 00:25:03,560
without having to implement a polygon
that maybe has two vertices going

483
00:25:03,560 --> 00:25:05,387
left to right on the screen.

484
00:25:05,387 --> 00:25:06,470
So that's what we do here.

485
00:25:06,470 --> 00:25:11,720
We have a ground body, which
is a static body, recall.

486
00:25:11,720 --> 00:25:14,150
Because the ground shouldn't move.

487
00:25:14,150 --> 00:25:18,101
We're going to change the
box into a dynamic body,

488
00:25:18,101 --> 00:25:19,350
but the ground shouldn't move.

489
00:25:19,350 --> 00:25:21,183
The ground should be
unaffected by anything.

490
00:25:21,183 --> 00:25:23,210
It's going to be static in our scene.

491
00:25:23,210 --> 00:25:25,400
And it's going to have an edge shape.

492
00:25:25,400 --> 00:25:28,850
So notice here, we take 0, 0 as the XY.

493
00:25:28,850 --> 00:25:31,220
And then a virtual width is zero.

494
00:25:31,220 --> 00:25:35,510
So with shapes, when
we define them here,

495
00:25:35,510 --> 00:25:39,690
it's not going to draw the shape
at 0, 0, at virtual width in 0.

496
00:25:39,690 --> 00:25:42,680
This is relative to wherever
the body is located.

497
00:25:42,680 --> 00:25:45,350
So wherever our body
is, this shape will be

498
00:25:45,350 --> 00:25:49,460
drawn with these coordinates, this
X and Y and this width and height,

499
00:25:49,460 --> 00:25:50,930
relative to that.

500
00:25:50,930 --> 00:25:56,130
And specifically, relative to the center
point of wherever we place a body.

501
00:25:56,130 --> 00:26:01,440
So if this ground is set to 0,
0 at virtual width and zero,

502
00:26:01,440 --> 00:26:03,440
where do we need to place
the actual body for it

503
00:26:03,440 --> 00:26:08,125
to render the ground appropriately?

504
00:26:08,125 --> 00:26:09,829
AUDIENCE: The middle bottom.

505
00:26:09,829 --> 00:26:12,370
COLTON OGDEN: Yeah, so we place
it towards the middle bottom.

506
00:26:12,370 --> 00:26:18,670
So we actually end up placing the body
itself here at virtual height minus 30.

507
00:26:18,670 --> 00:26:21,850
And when we affix this edge
shape to the body, we'll end up,

508
00:26:21,850 --> 00:26:24,280
even though it says 0,
0 virtual width zero,

509
00:26:24,280 --> 00:26:27,070
it's relative to wherever
the body's XY are.

510
00:26:27,070 --> 00:26:31,210
So it's actually going to be
0 virtual height minus 30,

511
00:26:31,210 --> 00:26:35,800
virtual width zero will
be where that edge exists.

512
00:26:35,800 --> 00:26:37,990
And then lastly, just
as we did with our box,

513
00:26:37,990 --> 00:26:41,980
we need a ground fixture so
that the ground body knows how

514
00:26:41,980 --> 00:26:43,820
it should interact with other things.

515
00:26:43,820 --> 00:26:47,350
So we're going to affix the edge
shape, which is just a line,

516
00:26:47,350 --> 00:26:49,870
to our ground body.

517
00:26:49,870 --> 00:26:53,410
And then here we do
love dot graphics-- just

518
00:26:53,410 --> 00:26:58,030
as we did with the love dot
graphics dot polygon for our box,

519
00:26:58,030 --> 00:27:00,931
we're going to do love dot graphics
dot line for our ground body.

520
00:27:00,931 --> 00:27:03,430
And we're going to do the exact
same thing, get world points

521
00:27:03,430 --> 00:27:06,510
and get points passing
the edge shape here.

522
00:27:06,510 --> 00:27:09,850
And I'm also setting
a line width of 2 just

523
00:27:09,850 --> 00:27:11,920
so we can see it a little bit better.

524
00:27:11,920 --> 00:27:13,580
And I'm going to color it red.

525
00:27:13,580 --> 00:27:17,770
Again, I colored the box up here green.

526
00:27:17,770 --> 00:27:20,570
So go ahead take a look
at what this looks like.

527
00:27:20,570 --> 00:27:24,280
So I'm going to go into ground.

528
00:27:24,280 --> 00:27:27,120


529
00:27:27,120 --> 00:27:30,460
And so notice-- and I also added
a little bit of restitution

530
00:27:30,460 --> 00:27:33,910
to the-- as I said before, restitution
is a quality that a fixture can

531
00:27:33,910 --> 00:27:35,890
have which gives it bounciness.

532
00:27:35,890 --> 00:27:38,350
So rather than just falling
flat down onto the ground,

533
00:27:38,350 --> 00:27:39,740
it bounces a little bit as well.

534
00:27:39,740 --> 00:27:42,323
And we can see the interaction,
so I'll play it one more time.

535
00:27:42,323 --> 00:27:43,630
It starts in the middle.

536
00:27:43,630 --> 00:27:46,600
And then as soon as it
hits the ground body

537
00:27:46,600 --> 00:27:49,840
that we created before, the edge
shape, it bounces a couple of times.

538
00:27:49,840 --> 00:27:54,580
But it shows that the box is
dynamic, but the ground is static.

539
00:27:54,580 --> 00:27:57,040
Nothing influences the
position of the ground.

540
00:27:57,040 --> 00:28:01,900
It gets hard set and will
stay there permanently.

541
00:28:01,900 --> 00:28:05,260
So that shows a nice,
easy simple demonstration

542
00:28:05,260 --> 00:28:09,820
of an interaction between a
static and a dynamic body.

543
00:28:09,820 --> 00:28:13,250
I'm going to go ahead and
pull up another example here.

544
00:28:13,250 --> 00:28:18,460
So kinematic, recall, what was
the difference between a kinematic

545
00:28:18,460 --> 00:28:21,298
and a static or dynamic body?

546
00:28:21,298 --> 00:28:23,798
AUDIENCE: Kinematic can move
but not influence other shapes.

547
00:28:23,798 --> 00:28:24,714
COLTON OGDEN: Correct.

548
00:28:24,714 --> 00:28:26,030
So a kinematic body can move.

549
00:28:26,030 --> 00:28:31,000
You can ascribe it positional velocity
or angular velocity, it's rotation.

550
00:28:31,000 --> 00:28:35,290
But when something collides with it,
it's not going to be influenced by it.

551
00:28:35,290 --> 00:28:38,530
It's going to influence the
body that it collides with.

552
00:28:38,530 --> 00:28:40,780
It's going to affect it
in some way, but nothing

553
00:28:40,780 --> 00:28:42,700
colliding with the
kinematic body is going

554
00:28:42,700 --> 00:28:45,790
to have an effect on its
position or its velocity.

555
00:28:45,790 --> 00:28:48,970
It's something that exists
and does something programmed

556
00:28:48,970 --> 00:28:50,920
and will just do that
indefinitely, but it

557
00:28:50,920 --> 00:28:55,260
will interact with other dynamic
bodies as we have programmed.

558
00:28:55,260 --> 00:28:57,760
And it will not interact with
other kinematic bodies either.

559
00:28:57,760 --> 00:29:00,280
They will almost pretend that
each other doesn't exist.

560
00:29:00,280 --> 00:29:03,785
If you overlap a static and a kinematic
body or kinematic and a kinematic body,

561
00:29:03,785 --> 00:29:06,160
they render on top of each
other, but they don't actually

562
00:29:06,160 --> 00:29:09,470
influence each other's
position or anything like that.

563
00:29:09,470 --> 00:29:13,695
So I'm going to go ahead and
run the kinematic example.

564
00:29:13,695 --> 00:29:19,550


565
00:29:19,550 --> 00:29:23,780
So here we have a few things going on.

566
00:29:23,780 --> 00:29:27,410
We have the box body that we
had before, the dynamic box that

567
00:29:27,410 --> 00:29:29,520
falls from the middle of the screen.

568
00:29:29,520 --> 00:29:31,700
We have the ground on the
very bottom to catch it.

569
00:29:31,700 --> 00:29:35,240
But we have three kinematic
boxes in the very center that

570
00:29:35,240 --> 00:29:39,440
are spinning that
influence the green box

571
00:29:39,440 --> 00:29:41,700
when the green box collides with them.

572
00:29:41,700 --> 00:29:44,510
So as you can see, it
tosses it around and then

573
00:29:44,510 --> 00:29:46,610
the green body falls back to the bottom.

574
00:29:46,610 --> 00:29:49,070
And in this example I've
taken away its restitution.

575
00:29:49,070 --> 00:29:53,300
So as soon as it hits the
ground, it just falls flat.

576
00:29:53,300 --> 00:29:54,870
Just like that.

577
00:29:54,870 --> 00:29:57,330
And so, as you can see, these
blue bodies, they're moving.

578
00:29:57,330 --> 00:30:00,830
They have angular velocity indefinitely.

579
00:30:00,830 --> 00:30:04,940
Specifically 360 degrees per second.

580
00:30:04,940 --> 00:30:09,080
And they will stay in that exact
position and rotate in that exact way

581
00:30:09,080 --> 00:30:10,080
forever.

582
00:30:10,080 --> 00:30:13,370
But as soon as they interact
with a dynamic body,

583
00:30:13,370 --> 00:30:16,670
they actually cause a collision
with that dynamic body.

584
00:30:16,670 --> 00:30:19,550
And the collision resolves
and this green body

585
00:30:19,550 --> 00:30:21,710
gets tossed around because it's dynamic.

586
00:30:21,710 --> 00:30:27,350
It will basically do whatever it
can to interact with the game world

587
00:30:27,350 --> 00:30:30,590
as long as it's interacting
with other bodies

588
00:30:30,590 --> 00:30:32,270
and resolving its collision that way.

589
00:30:32,270 --> 00:30:34,800


590
00:30:34,800 --> 00:30:39,860
And so that's the key example between
what the three different bodies are

591
00:30:39,860 --> 00:30:40,580
fundamentally.

592
00:30:40,580 --> 00:30:45,182
And with these three body types you
can construct pretty much any scene

593
00:30:45,182 --> 00:30:45,890
that you want to.

594
00:30:45,890 --> 00:30:50,180
And obviously the bodies and the
fixtures can get insanely complex.

595
00:30:50,180 --> 00:30:55,010
I mean, we can look back
here at this first example.

596
00:30:55,010 --> 00:31:05,780
These structures are a composition of
many different types of dynamic bodies

597
00:31:05,780 --> 00:31:11,330
that have been given anchors and
joints and all sorts of other things

598
00:31:11,330 --> 00:31:15,170
to make them look as if
they're big constructions.

599
00:31:15,170 --> 00:31:18,370
But at the end, they're all
just a bunch of little bodies

600
00:31:18,370 --> 00:31:20,870
that are welded together,
fixtures that are welded together.

601
00:31:20,870 --> 00:31:23,480


602
00:31:23,480 --> 00:31:27,710
And these fundamental building blocks
are how you construct scenes like this.

603
00:31:27,710 --> 00:31:32,210
Put a bunch of these blocks together,
weld them together with joints,

604
00:31:32,210 --> 00:31:33,050
in this case.

605
00:31:33,050 --> 00:31:35,840
We won't cover joints in
the context of this lecture.

606
00:31:35,840 --> 00:31:39,290
But if you're wondering how
all of these individual things

607
00:31:39,290 --> 00:31:44,729
can be collideable while still
constructing these massive scenes

608
00:31:44,729 --> 00:31:46,520
and having physics
applied to them, they're

609
00:31:46,520 --> 00:31:51,140
just jointed together using weld joints
or other types of joints, pulley joints

610
00:31:51,140 --> 00:31:52,640
depending on what they are.

611
00:31:52,640 --> 00:31:58,760
In this case, there is two circle
shapes here, circle fixtures,

612
00:31:58,760 --> 00:32:01,190
that are the wheels
on this cart and then

613
00:32:01,190 --> 00:32:06,740
they're welded to the
flat constructions here.

614
00:32:06,740 --> 00:32:09,980
Allowing those to be dynamic allows
the wheels to roll, and therefore

615
00:32:09,980 --> 00:32:12,650
carry the other load with it.

616
00:32:12,650 --> 00:32:14,390
Same with this bridge.

617
00:32:14,390 --> 00:32:18,710
I forget the exact name of the joint,
but it's a chain of fixtures together

618
00:32:18,710 --> 00:32:20,720
that are welded by a
specific kind of joint.

619
00:32:20,720 --> 00:32:23,090
And by putting them
together in this way,

620
00:32:23,090 --> 00:32:27,740
you get a bridge and all sorts of
things that you could think of,

621
00:32:27,740 --> 00:32:33,830
including tanks, which
is in the notes here.

622
00:32:33,830 --> 00:32:36,080
This third link, one
of them talks about how

623
00:32:36,080 --> 00:32:37,970
to implement a tank
by having treads going

624
00:32:37,970 --> 00:32:40,580
around circles and then a massive body.

625
00:32:40,580 --> 00:32:45,156
You could do anything with
Box2D, it's an awesome library.

626
00:32:45,156 --> 00:32:47,030
In the context of Angry
Birds, really we just

627
00:32:47,030 --> 00:32:49,400
scratched the surface for
what is possible here.

628
00:32:49,400 --> 00:32:52,470


629
00:32:52,470 --> 00:32:54,590
So I'm going to demo now.

630
00:32:54,590 --> 00:32:59,480
Actually, I enjoyed, I think,
this demo, this bit of code,

631
00:32:59,480 --> 00:33:03,410
more than I enjoyed the
Angry Birds implementation.

632
00:33:03,410 --> 00:33:06,400
And it's a program that
I wrote called Ball Pit.

633
00:33:06,400 --> 00:33:08,160
Oh, by the way, before I get into that.

634
00:33:08,160 --> 00:33:11,840
So I'll leave that as a
little teaser, I guess.

635
00:33:11,840 --> 00:33:15,440
Looking at kinematic, really quickly.

636
00:33:15,440 --> 00:33:18,590
We're going to look and
see that I've created

637
00:33:18,590 --> 00:33:23,450
a table for the kinematic
bodies, a table for the fixtures,

638
00:33:23,450 --> 00:33:24,802
and then one shape.

639
00:33:24,802 --> 00:33:26,510
Because you only need
one shape actually,

640
00:33:26,510 --> 00:33:28,400
and you can apply one
shape to as many bodies

641
00:33:28,400 --> 00:33:32,960
as you want to as long as
they all have the same shape.

642
00:33:32,960 --> 00:33:35,690
I just create three
kinematic bodies here.

643
00:33:35,690 --> 00:33:39,590
So spacing them out relative to
the center with this math here.

644
00:33:39,590 --> 00:33:41,019
They get the string kinematic.

645
00:33:41,019 --> 00:33:42,560
And that's really the key difference.

646
00:33:42,560 --> 00:33:45,830
And then before finishing,
I make sure that I

647
00:33:45,830 --> 00:33:47,920
set them to have an angular velocity.

648
00:33:47,920 --> 00:33:49,400
So this is how you spin something.

649
00:33:49,400 --> 00:33:51,483
If you want to set something
to spin indefinitely,

650
00:33:51,483 --> 00:33:52,730
just set an angular velocity.

651
00:33:52,730 --> 00:33:56,540
In this case, 360 times
degrees to radians.

652
00:33:56,540 --> 00:34:01,880
And that's just a formula written out as
a constant, which is just the number--

653
00:34:01,880 --> 00:34:05,942
I forget offhand what
exactly the formula is.

654
00:34:05,942 --> 00:34:06,650
But it's up here.

655
00:34:06,650 --> 00:34:13,070
It's degrees to radians
0.01745329, et cetera.

656
00:34:13,070 --> 00:34:15,949
But just like pi, it's
a number that you can

657
00:34:15,949 --> 00:34:19,540
use to multiply a number in degrees,
and you'll get a number in radians.

658
00:34:19,540 --> 00:34:22,120
And there's the reverse
up there as well.

659
00:34:22,120 --> 00:34:26,949
We have to do this because Box2D
expects, for any types of rotation,

660
00:34:26,949 --> 00:34:28,239
it expects it in radians.

661
00:34:28,239 --> 00:34:30,050
I prefer thinking in degrees.

662
00:34:30,050 --> 00:34:33,370
So I passed in 360 times
degrees to radians.

663
00:34:33,370 --> 00:34:37,340
And so we render down here, just
as we did with the box body.

664
00:34:37,340 --> 00:34:42,790
We render the kinematic bodies,
polygon fill, kinematic bodies at i

665
00:34:42,790 --> 00:34:45,639
get world points kinematic
shape get points.

666
00:34:45,639 --> 00:34:47,179
Nothing terribly different.

667
00:34:47,179 --> 00:34:50,949
The only real key difference is that
we've added kinematic as a string

668
00:34:50,949 --> 00:34:53,659
to the constructor for the body.

669
00:34:53,659 --> 00:34:55,810
And we've added some angular velocity.

670
00:34:55,810 --> 00:34:58,082
And recall, this will
make it spin indefinitely,

671
00:34:58,082 --> 00:35:00,790
but it will never be influenced--
its angular velocity will never

672
00:35:00,790 --> 00:35:03,850
be influenced, its position
will never be influenced

673
00:35:03,850 --> 00:35:06,310
by anything else in our scene.

674
00:35:06,310 --> 00:35:10,060
So now with that out of the way,
I'm going to pull up Ball Pit.

675
00:35:10,060 --> 00:35:13,170


676
00:35:13,170 --> 00:35:15,590
And maybe I'm just a little
bit too excited about this.

677
00:35:15,590 --> 00:35:18,160
But I enjoyed this a lot.

678
00:35:18,160 --> 00:35:22,300
So what it is, is this is
like a bigger demonstration

679
00:35:22,300 --> 00:35:24,680
of putting all these pieces together.

680
00:35:24,680 --> 00:35:26,994
We have a bunch of circle shapes.

681
00:35:26,994 --> 00:35:28,660
They're all interacting with each other.

682
00:35:28,660 --> 00:35:29,770
They all have physics.

683
00:35:29,770 --> 00:35:33,190
And then I have a larger
shape here, this square,

684
00:35:33,190 --> 00:35:35,510
which has a higher density
than everything else.

685
00:35:35,510 --> 00:35:38,660
And by pressing Spacebar
I can just dive into--

686
00:35:38,660 --> 00:35:41,440
throw it into the ball pit,
and it'll cause an interaction

687
00:35:41,440 --> 00:35:42,670
with everything else.

688
00:35:42,670 --> 00:35:46,780
And a bug slash feature
that I discovered

689
00:35:46,780 --> 00:35:51,070
about this is that if you press
Spacebar over and over again,

690
00:35:51,070 --> 00:35:53,510
it never resets its velocity.

691
00:35:53,510 --> 00:35:55,854
So it just slams down into the ball pit.

692
00:35:55,854 --> 00:35:58,270
So it's just kind of fun, and
I think there might actually

693
00:35:58,270 --> 00:36:00,580
be possibly a game idea in here.

694
00:36:00,580 --> 00:36:02,710
But, I mean, well, what
are the pieces here?

695
00:36:02,710 --> 00:36:04,000
What's different about this?

696
00:36:04,000 --> 00:36:07,388


697
00:36:07,388 --> 00:36:10,949
AUDIENCE: They're all dynamic shapes.

698
00:36:10,949 --> 00:36:11,740
COLTON OGDEN: Yeah.

699
00:36:11,740 --> 00:36:13,490
So they're all dynamic shapes.

700
00:36:13,490 --> 00:36:15,410
Except for the ground
at the very bottom.

701
00:36:15,410 --> 00:36:21,994
And also, hidden from view are
actually two more static shapes

702
00:36:21,994 --> 00:36:22,910
on the left and right.

703
00:36:22,910 --> 00:36:25,160
Because if we didn't have
those, all of the balls

704
00:36:25,160 --> 00:36:28,520
would fall to the side out of view.

705
00:36:28,520 --> 00:36:33,020
But yeah, we have the static
delimiters for our scene.

706
00:36:33,020 --> 00:36:38,420
But we have a bunch of dynamic
bodies, the balls are all dynamic.

707
00:36:38,420 --> 00:36:42,470
And then the square is also dynamic.

708
00:36:42,470 --> 00:36:45,387
And then, like I said before, the
only real difference between them

709
00:36:45,387 --> 00:36:47,220
is that obviously the
square is a rectangle.

710
00:36:47,220 --> 00:36:49,200
But it also just has a higher density.

711
00:36:49,200 --> 00:36:53,027
And so by giving it a higher density
it pushes everything else-- oh,

712
00:36:53,027 --> 00:36:53,860
what happened there?

713
00:36:53,860 --> 00:36:54,485
That was weird.

714
00:36:54,485 --> 00:36:57,410
It pushes-- I think it went to
sleep because we didn't do anything

715
00:36:57,410 --> 00:36:57,980
for a while.

716
00:36:57,980 --> 00:37:01,550
But it's able to fall
through everything else

717
00:37:01,550 --> 00:37:05,960
because it knows that it's heavier,
and that it should push and apply

718
00:37:05,960 --> 00:37:09,800
a larger force to everything
else that's around it.

719
00:37:09,800 --> 00:37:14,030
And so by using these fundamental
building blocks of what Box2D is,

720
00:37:14,030 --> 00:37:18,320
you can construct a lot of really cool
simulations and other fun programs

721
00:37:18,320 --> 00:37:20,840
and actually get interesting game ideas.

722
00:37:20,840 --> 00:37:25,010
I'm inclined to believe that Angry Birds
started out as somebody messing around

723
00:37:25,010 --> 00:37:27,780
with the Box2D, or
physics engine like this.

724
00:37:27,780 --> 00:37:31,430
And it was inspired by some other game
that I should look into a little bit.

725
00:37:31,430 --> 00:37:34,837
But the creators of that game,
presumably, found this physics engine

726
00:37:34,837 --> 00:37:36,170
and were like, oh, this is cool.

727
00:37:36,170 --> 00:37:39,650
I'm going to put a tower of blocks
here and just throw something at it.

728
00:37:39,650 --> 00:37:42,130
And then they realized, oh, we
can make a game out of this.

729
00:37:42,130 --> 00:37:46,890
And so I encourage you, if you're ever
curious to just experiment with things

730
00:37:46,890 --> 00:37:47,390
like that.

731
00:37:47,390 --> 00:37:49,040
We could probably turn this into a game.

732
00:37:49,040 --> 00:37:49,581
I don't know.

733
00:37:49,581 --> 00:37:50,480
I like this a lot.

734
00:37:50,480 --> 00:38:00,050
It's a good segue from the abstract,
for lack of a better word, examples

735
00:38:00,050 --> 00:38:05,030
that we used earlier, and
merges it more into the realm

736
00:38:05,030 --> 00:38:09,230
of how can we make
something fun with this?

737
00:38:09,230 --> 00:38:14,570
And so that's how we're going to
start moving into the distro today.

738
00:38:14,570 --> 00:38:21,320
So the main topic of today's lecture is
Box2D and how we use it to make a game.

739
00:38:21,320 --> 00:38:23,780
Another thing that we should
consider is mouse input.

740
00:38:23,780 --> 00:38:25,480
We haven't really used it yet.

741
00:38:25,480 --> 00:38:29,450
And I believe I've mentioned
it before, slightly offhand.

742
00:38:29,450 --> 00:38:31,060
But Love2D makes it super easy.

743
00:38:31,060 --> 00:38:33,761
It's just like we do
with keyboard input.

744
00:38:33,761 --> 00:38:36,260
We just have a couple of callbacks
that are in main dot Lua,

745
00:38:36,260 --> 00:38:38,390
mouse pressed and mouse released.

746
00:38:38,390 --> 00:38:41,705
The difference between these
and key pressed and key

747
00:38:41,705 --> 00:38:45,500
released is that they also get
an X and a Y. Because usually,

748
00:38:45,500 --> 00:38:47,420
when you click the mouse
or release the mouse,

749
00:38:47,420 --> 00:38:49,461
you want to know where it
happened because that's

750
00:38:49,461 --> 00:38:53,250
obviously pertinent to what you're
doing when you're using a mouse.

751
00:38:53,250 --> 00:38:58,940
So these are fired by Love2D every time
you click or release a mouse button.

752
00:38:58,940 --> 00:39:01,670
And they get the X the
Y and the key, and you

753
00:39:01,670 --> 00:39:03,350
can do whatever you want with those.

754
00:39:03,350 --> 00:39:05,900
And just as we've done
in prior lectures so

755
00:39:05,900 --> 00:39:10,220
that we can use mouse input in
other modules besides main dot Lua,

756
00:39:10,220 --> 00:39:13,505
there's a function called love
dot mouse dot key pressed and key

757
00:39:13,505 --> 00:39:15,341
released that I implemented
in main dot Lua.

758
00:39:15,341 --> 00:39:16,340
You can check those out.

759
00:39:16,340 --> 00:39:20,540
They're very similar to how we did the
input tables for the keyboard before.

760
00:39:20,540 --> 00:39:24,020
But they allow us to use
this functionality inside

761
00:39:24,020 --> 00:39:30,350
of other functions, other
modules, besides main dot Lua.

762
00:39:30,350 --> 00:39:35,180
So let's go ahead and start looking at--

763
00:39:35,180 --> 00:39:42,140
this is where we're going to start
looking at the distro for Angry Birds

764
00:39:42,140 --> 00:39:46,489
and how we can take all these pieces
and form them into an actual game.

765
00:39:46,489 --> 00:39:49,530
So the first thing we'll do, we'll
take a look at just a couple of things

766
00:39:49,530 --> 00:39:51,530
and then we'll take a
short break and then we'll

767
00:39:51,530 --> 00:39:53,150
get more into the meat of it.

768
00:39:53,150 --> 00:39:55,820
But let me go ahead and
clear out all of these.

769
00:39:55,820 --> 00:39:58,800


770
00:39:58,800 --> 00:40:02,460
And then we're going to pull up--
so the distro is in Angry 50.

771
00:40:02,460 --> 00:40:06,270
And so main dot Lua is here.

772
00:40:06,270 --> 00:40:08,280
So not a whole lot is different in here.

773
00:40:08,280 --> 00:40:11,700
So we have two states in our game.

774
00:40:11,700 --> 00:40:14,490
So we had a start and a play
state, as we saw before.

775
00:40:14,490 --> 00:40:16,810
The start state is
like we've done before.

776
00:40:16,810 --> 00:40:20,070
The only difference is in this
start state, well, for one,

777
00:40:20,070 --> 00:40:22,020
it's running a Box2D simulation.

778
00:40:22,020 --> 00:40:25,800
And two, we're actually
using mouse input.

779
00:40:25,800 --> 00:40:27,780
So actually, let's
look at main so you can

780
00:40:27,780 --> 00:40:31,540
see where I've added this,
which is different than before.

781
00:40:31,540 --> 00:40:35,310
So we have love dot key
pressed, as we've seen before.

782
00:40:35,310 --> 00:40:38,520
But we also have mouse
pressed and mouse released.

783
00:40:38,520 --> 00:40:40,660
And then mouse was pressed
and mouse was released.

784
00:40:40,660 --> 00:40:44,340
So those are the main differences in
main dot Lua this time, as opposed

785
00:40:44,340 --> 00:40:49,020
to last prior lectures, which
we only had keyboard input.

786
00:40:49,020 --> 00:40:53,490
And as you can see here, we have input
tables for keys pressed and released

787
00:40:53,490 --> 00:40:54,570
on the mouse.

788
00:40:54,570 --> 00:40:57,870
And so we initialized those
to empty on every update frame

789
00:40:57,870 --> 00:41:00,840
just like we've done with the keyboard.

790
00:41:00,840 --> 00:41:05,820
And then the input tables get
updated in the callback functions

791
00:41:05,820 --> 00:41:07,517
as we've done before.

792
00:41:07,517 --> 00:41:10,600
And so that's basically all that's
different about main dot Lua this time.

793
00:41:10,600 --> 00:41:15,540
And that's how we've tied together the
new mouse functions that we've just

794
00:41:15,540 --> 00:41:17,040
looked at into our game.

795
00:41:17,040 --> 00:41:19,830


796
00:41:19,830 --> 00:41:24,270
The states that exist in our game
are play state and start state.

797
00:41:24,270 --> 00:41:25,110
So very simple.

798
00:41:25,110 --> 00:41:27,480
Very similar to last week
where we looked at Zelda,

799
00:41:27,480 --> 00:41:31,470
we only basically had a
start state and a play state.

800
00:41:31,470 --> 00:41:37,860
The start state, we can see
here, just to tie together

801
00:41:37,860 --> 00:41:41,160
the last bit of our usage of the mouse.

802
00:41:41,160 --> 00:41:43,920
Love dot mouse dot was pressed 1.

803
00:41:43,920 --> 00:41:46,695
Does anybody know what this 1 is?

804
00:41:46,695 --> 00:41:48,120
AUDIENCE: Is that left click?

805
00:41:48,120 --> 00:41:49,411
COLTON OGDEN: It is left click.

806
00:41:49,411 --> 00:41:53,850
So Love2D assigns integer values
to all of your mouse buttons.

807
00:41:53,850 --> 00:41:58,230
And 1 is traditionally the
default value for left click.

808
00:41:58,230 --> 00:42:00,420
Some frameworks will use 0.

809
00:42:00,420 --> 00:42:06,300
But Lua, 1 index so start
with 1 instead of 0.

810
00:42:06,300 --> 00:42:10,810
The thing about the start state here
that's kind of cool and interesting.

811
00:42:10,810 --> 00:42:18,030
So I'm going to go ahead
and play it again, the game.

812
00:42:18,030 --> 00:42:21,440
So we start off and right off the
gate, just to make things interesting

813
00:42:21,440 --> 00:42:23,940
rather than just have a
static screen that says

814
00:42:23,940 --> 00:42:28,050
Anger 50 click to start, we're
actually running a Love2D,

815
00:42:28,050 --> 00:42:30,790
a Box2D simulation here.

816
00:42:30,790 --> 00:42:33,720
It's a world with a bunch of squares.

817
00:42:33,720 --> 00:42:37,812
And so what kind of
bodies are all of these?

818
00:42:37,812 --> 00:42:38,810
AUDIENCE: [INAUDIBLE].

819
00:42:38,810 --> 00:42:40,518
COLTON OGDEN: They're
all dynamic bodies.

820
00:42:40,518 --> 00:42:44,210
And we've encapsulated them all, just as
we did before in the ball pit example,

821
00:42:44,210 --> 00:42:47,895
with some invisible static bodies on the
left, right, and bottom of the screen.

822
00:42:47,895 --> 00:42:49,770
Because if we didn't
have those static bodies

823
00:42:49,770 --> 00:42:52,980
they would just fall all the way down.

824
00:42:52,980 --> 00:42:56,100
And the nice thing is we don't
actually have to render anything.

825
00:42:56,100 --> 00:43:01,850
So if you want maybe an invisible
barrier for something in your game,

826
00:43:01,850 --> 00:43:04,364
or you want to encapsulate
something, something physical,

827
00:43:04,364 --> 00:43:05,780
you don't have to render anything.

828
00:43:05,780 --> 00:43:10,160
You can just have arbitrarily
shaped and positioned static bodies.

829
00:43:10,160 --> 00:43:11,977
And that will act as a container.

830
00:43:11,977 --> 00:43:13,310
So that's all we're doing there.

831
00:43:13,310 --> 00:43:17,960
We have a container set for all
of our little square alien guys.

832
00:43:17,960 --> 00:43:22,580
And by creating, I think, a hundred
of them and just letting them drop,

833
00:43:22,580 --> 00:43:27,140
we have this interesting
visual start to our game

834
00:43:27,140 --> 00:43:29,310
with very, very minimal effort.

835
00:43:29,310 --> 00:43:31,340
So we can take a look at this.

836
00:43:31,340 --> 00:43:36,260
So in our start state init, as
I said before, we have a world.

837
00:43:36,260 --> 00:43:38,570
We obviously need a member of new world.

838
00:43:38,570 --> 00:43:40,670
Anytime we do any Box2D
stuff you have to start

839
00:43:40,670 --> 00:43:43,185
by having a love dot
physics dot new world,

840
00:43:43,185 --> 00:43:46,730
else you won't be able
to run any simulations.

841
00:43:46,730 --> 00:43:51,740
Going to create a ground, walls,
and then a bunch of aliens.

842
00:43:51,740 --> 00:43:57,630
So this here, we can see that we have a
table that we're inserting aliens into.

843
00:43:57,630 --> 00:44:00,980
But we have a class called alien.

844
00:44:00,980 --> 00:44:04,520
So anybody want to ballpark
what an alien class ultimately

845
00:44:04,520 --> 00:44:05,930
encapsulates or ultimately is?

846
00:44:05,930 --> 00:44:10,421


847
00:44:10,421 --> 00:44:15,694
AUDIENCE: Probably the way
it looks, like the skin.

848
00:44:15,694 --> 00:44:18,110
COLTON OGDEN: It is, yeah,
that's definitely a part of it.

849
00:44:18,110 --> 00:44:19,880
So the way it looks, or it's skin.

850
00:44:19,880 --> 00:44:23,210
So it does have a reference to that.

851
00:44:23,210 --> 00:44:31,970
And then more functionally, it also
possesses a body and a fixture.

852
00:44:31,970 --> 00:44:35,000
So rather than having a
bunch of bodies and fixtures

853
00:44:35,000 --> 00:44:38,780
that are separated out
and maybe just in tables

854
00:44:38,780 --> 00:44:44,240
at the surface level of whatever,
our level, just wrap them in a class.

855
00:44:44,240 --> 00:44:46,370
And then we just can
maintain a reference

856
00:44:46,370 --> 00:44:50,630
to each individual alien's
body and fixture that way.

857
00:44:50,630 --> 00:44:53,240
So it's a little bit more encapsulated.

858
00:44:53,240 --> 00:44:57,500
It's a little bit more object oriented,
little bit cleaner in my opinion.

859
00:44:57,500 --> 00:45:03,230
The alien class can take
square or round as its--

860
00:45:03,230 --> 00:45:05,900
well, it can take anything
you want to as its type.

861
00:45:05,900 --> 00:45:09,290
So this will ultimately decide how
it's rendered and what shape it gets.

862
00:45:09,290 --> 00:45:13,670
But if it's square, which is
the default, so if you just

863
00:45:13,670 --> 00:45:18,020
create an alien with
no type, it will get

864
00:45:18,020 --> 00:45:21,350
a love dot physics dot rectangle shape.

865
00:45:21,350 --> 00:45:23,720
So as we saw before, that's just a box.

866
00:45:23,720 --> 00:45:26,510
And then if not, we just
default to circle shape.

867
00:45:26,510 --> 00:45:29,450
But you could program it to
take in whatever shape you want,

868
00:45:29,450 --> 00:45:30,980
and then just give it that shape.

869
00:45:30,980 --> 00:45:33,230
And you don't really
have to do much in terms

870
00:45:33,230 --> 00:45:36,890
of coding how it interacts with anything
else in terms of collision, at least.

871
00:45:36,890 --> 00:45:40,220
Because, thankfully, Box2D
will know, OK, it's a circle.

872
00:45:40,220 --> 00:45:43,790
It should spin around and interact
with things like a circle.

873
00:45:43,790 --> 00:45:47,090
Or it's a rectangle so it should
interact with things like it's a box.

874
00:45:47,090 --> 00:45:48,680
Just nice and convenient.

875
00:45:48,680 --> 00:45:52,070
And then we'll just
create a fixture here.

876
00:45:52,070 --> 00:45:55,860
This set user data
function here is important

877
00:45:55,860 --> 00:46:01,850
because we'll see in the context of
how we actually resolve collisions

878
00:46:01,850 --> 00:46:05,300
in a customized way,
we'll need user data

879
00:46:05,300 --> 00:46:08,840
to be able to differentiate
what gets collided in our world.

880
00:46:08,840 --> 00:46:14,900
But at the moment you can just know that
this basically allows us to pass in--

881
00:46:14,900 --> 00:46:17,720
to set arbitrary data onto a fixture.

882
00:46:17,720 --> 00:46:22,850
So we can say, fixture set user
data alien, the string alien.

883
00:46:22,850 --> 00:46:28,520
And what that means is that fixture has
some customized metadata about it that

884
00:46:28,520 --> 00:46:30,290
says, this is an alien.

885
00:46:30,290 --> 00:46:31,892
It's whatever we want to do with it.

886
00:46:31,892 --> 00:46:33,350
We could give this a table as well.

887
00:46:33,350 --> 00:46:35,570
We could just say, the
user data is a table

888
00:46:35,570 --> 00:46:40,190
and then has a bunch of information
that we can then use at collision time

889
00:46:40,190 --> 00:46:42,050
to perform different work on it.

890
00:46:42,050 --> 00:46:44,210
But this set user data
function is how we

891
00:46:44,210 --> 00:46:48,900
are able to resolve collisions between
obstacles and aliens differently than,

892
00:46:48,900 --> 00:46:53,460
say players and aliens, or
even the alien and the ground.

893
00:46:53,460 --> 00:46:57,110
Because when we do any Box2D
collision, right, the world's

894
00:46:57,110 --> 00:46:59,150
taking care of the collisions for us.

895
00:46:59,150 --> 00:47:04,460
How do we tell the world, OK, when I
hit the ground I want to play a sound,

896
00:47:04,460 --> 00:47:05,810
but not do anything.

897
00:47:05,810 --> 00:47:10,130
If I hit this box at this
velocity, I want it to destroy it.

898
00:47:10,130 --> 00:47:12,860
If I hit the alien, I want
the alien to disappear

899
00:47:12,860 --> 00:47:16,280
and I want to show a victory label.

900
00:47:16,280 --> 00:47:18,890
How do we do all these different things?

901
00:47:18,890 --> 00:47:21,770
We do that with what are
called collision callbacks

902
00:47:21,770 --> 00:47:23,400
in the context of Box2D.

903
00:47:23,400 --> 00:47:24,720
And we'll see how that works.

904
00:47:24,720 --> 00:47:30,870
But suffice to say, user data will
be very important coming forward.

905
00:47:30,870 --> 00:47:33,350
And then this launched false,
actually we don't end up

906
00:47:33,350 --> 00:47:34,910
using this so this is irrelevant.

907
00:47:34,910 --> 00:47:43,190
But it has a render function here,
which just takes in the bodies X and Y

908
00:47:43,190 --> 00:47:46,242
and will draw it at
the angle that it's at.

909
00:47:46,242 --> 00:47:47,450
So that's an important thing.

910
00:47:47,450 --> 00:47:52,400
When we before, what we were doing
is drawing things via shapes.

911
00:47:52,400 --> 00:47:55,790
So love dot graphics dot polygon,
love dot graphics dot circle,

912
00:47:55,790 --> 00:47:57,710
love dot graphics dot line.

913
00:47:57,710 --> 00:48:03,440
But if we want to draw
a sprite instead, we

914
00:48:03,440 --> 00:48:06,440
need to draw it at the right
position, first of all, right?

915
00:48:06,440 --> 00:48:09,890
And then things also rotate in Box2D.

916
00:48:09,890 --> 00:48:13,500
So we need to draw it
at the right angle.

917
00:48:13,500 --> 00:48:17,270
So what we do is we can actually
query the body for its X.

918
00:48:17,270 --> 00:48:21,770
We can query the body for its Y. And we
can also query the body for its angle.

919
00:48:21,770 --> 00:48:24,560
And then we can draw
the texture and the quad

920
00:48:24,560 --> 00:48:28,470
that we want to using
those XY and the angle,

921
00:48:28,470 --> 00:48:33,560
and that will have the effect of
drawing a sprite in the world that

922
00:48:33,560 --> 00:48:37,190
mirrors what's going on in Box2D,
rather than just a simple shape.

923
00:48:37,190 --> 00:48:42,260
So that's as simple as it is for
drawing a sprite instead of a shape.

924
00:48:42,260 --> 00:48:46,230
You can see here, the 17.5 17.5.

925
00:48:46,230 --> 00:48:48,404
Does anybody know what that's for?

926
00:48:48,404 --> 00:48:49,240
AUDIENCE: Not sure.

927
00:48:49,240 --> 00:48:52,940
COLTON OGDEN: So 17.5 17.5 at
the end is half of the width

928
00:48:52,940 --> 00:48:56,030
and half of the height of the aliens.

929
00:48:56,030 --> 00:48:58,670
So aliens are 35 by 35 in this game.

930
00:48:58,670 --> 00:49:00,050
We pass those in.

931
00:49:00,050 --> 00:49:02,450
This is the center of origin.

932
00:49:02,450 --> 00:49:05,600
So when we rotate something
by center of origin,

933
00:49:05,600 --> 00:49:11,620
it basically describes where the
rotation is going to take place.

934
00:49:11,620 --> 00:49:15,237
So if it's rotated about the top
left and we rotate something,

935
00:49:15,237 --> 00:49:17,570
it's going to have the effect
of the sprite going around

936
00:49:17,570 --> 00:49:20,150
in a circle in sort of an odd way.

937
00:49:20,150 --> 00:49:23,960
If we rotate the sprite based on the
center of origin of the actual sprite

938
00:49:23,960 --> 00:49:28,760
itself, that will have the effect of
rotating the sprite on its center.

939
00:49:28,760 --> 00:49:31,520
So you can set that origin
wherever you want to

940
00:49:31,520 --> 00:49:35,180
and it'll perform a 360 degree
rotation about that point.

941
00:49:35,180 --> 00:49:37,590
And we're setting that point to half--

942
00:49:37,590 --> 00:49:40,040
to basically the middle of
where we're drawing the sprite.

943
00:49:40,040 --> 00:49:42,720
So that will have the effect of
when we give it this angle here,

944
00:49:42,720 --> 00:49:46,880
self dot body to get angle, the
rotation will take place in place.

945
00:49:46,880 --> 00:49:50,570
It won't take place-- it won't be some
sort of weird about the top left corner

946
00:49:50,570 --> 00:49:52,770
rotation, which is not what we want.

947
00:49:52,770 --> 00:49:55,840
So when you see center of
origin being modified like that,

948
00:49:55,840 --> 00:49:58,610
you can assume that it's
because we have an offset

949
00:49:58,610 --> 00:50:01,550
and we're trying to find the
center of where we're drawing

950
00:50:01,550 --> 00:50:04,980
and rotate about that to
do an in place rotation.

951
00:50:04,980 --> 00:50:08,720
But not necessarily, you
could also draw something.

952
00:50:08,720 --> 00:50:12,800
You could also, maybe you want something
some sort of magical ball of energy

953
00:50:12,800 --> 00:50:15,230
to rotate about a rod or something.

954
00:50:15,230 --> 00:50:17,780
And so you want it to rotate
around a different center,

955
00:50:17,780 --> 00:50:20,660
or whatever you want arbitrarily.

956
00:50:20,660 --> 00:50:23,840
But typically, at least
mostly that I've seen,

957
00:50:23,840 --> 00:50:27,950
this is useful for making sure that
your rotations, your in place rotations,

958
00:50:27,950 --> 00:50:29,360
are accurately rendered.

959
00:50:29,360 --> 00:50:33,320
So any questions about
how the alien class works?

960
00:50:33,320 --> 00:50:36,860


961
00:50:36,860 --> 00:50:38,340
All right.

962
00:50:38,340 --> 00:50:40,650
So that's the alien class.

963
00:50:40,650 --> 00:50:44,160
That's the basically the fundamental
building block of our game.

964
00:50:44,160 --> 00:50:48,120
The other part is the obstacle.

965
00:50:48,120 --> 00:50:50,280
We have obstacles and we have aliens.

966
00:50:50,280 --> 00:50:53,610
The obstacles and aliens
are actually very similar.

967
00:50:53,610 --> 00:50:55,560
So what's the difference between--

968
00:50:55,560 --> 00:50:58,080
I mean, ultimately,
how are they similar?

969
00:50:58,080 --> 00:51:03,470


970
00:51:03,470 --> 00:51:05,430
AUDIENCE: They're both
dynamic [INAUDIBLE]..

971
00:51:05,430 --> 00:51:07,580
COLTON OGDEN: They're
both dynamic bodies, yeah.

972
00:51:07,580 --> 00:51:11,720
Really, the only thing that's
different about a obstacle and an alien

973
00:51:11,720 --> 00:51:14,570
is what we do with them in our
scene and how they're rendered.

974
00:51:14,570 --> 00:51:16,760
But they function very similarly.

975
00:51:16,760 --> 00:51:18,950
They're just dynamic bodies
that we give a shape to

976
00:51:18,950 --> 00:51:21,200
and we render them with that shape.

977
00:51:21,200 --> 00:51:24,680


978
00:51:24,680 --> 00:51:28,670
In this case, the obstacle
constructor, we've

979
00:51:28,670 --> 00:51:33,540
decided to design it such that it could
take a shape horizontal or vertical,

980
00:51:33,540 --> 00:51:36,620
which is similar to the type that
we saw before with the alien,

981
00:51:36,620 --> 00:51:38,840
where it could be square or circular.

982
00:51:38,840 --> 00:51:45,860
In this case, if we look back
at our sprite sheet back here,

983
00:51:45,860 --> 00:51:48,124
we can see there's a
ton of different shapes.

984
00:51:48,124 --> 00:51:51,290
But the only two shapes that we're going
to use in the context of this game,

985
00:51:51,290 --> 00:51:55,970
just for this demonstration, are the
horizontal, clean wooden shape here

986
00:51:55,970 --> 00:51:59,150
and the vertical one that's right here.

987
00:51:59,150 --> 00:52:02,120
And so in order to find
those out I had to open up

988
00:52:02,120 --> 00:52:05,567
basically this sprite
in my sprite editor,

989
00:52:05,567 --> 00:52:08,150
figure out where the XY width
and height were, and then create

990
00:52:08,150 --> 00:52:10,340
a quad manually off of that.

991
00:52:10,340 --> 00:52:14,120
And then I edited the util
dot Lua-- or not util dot Lua,

992
00:52:14,120 --> 00:52:17,480
the dependencies dot Lua here.

993
00:52:17,480 --> 00:52:21,050
Normally we just create gframes
and then we use generate quads.

994
00:52:21,050 --> 00:52:25,460
And you can do that like with the
aliens and with the tiles, the tiles

995
00:52:25,460 --> 00:52:28,190
being this sprite sheet that--

996
00:52:28,190 --> 00:52:29,510
this one right here.

997
00:52:29,510 --> 00:52:31,310
These are 35 by 35.

998
00:52:31,310 --> 00:52:32,720
These are 35 by 35.

999
00:52:32,720 --> 00:52:34,130
These are not 35 by 35.

1000
00:52:34,130 --> 00:52:38,280
These are a bunch of
different shapes and sizes.

1001
00:52:38,280 --> 00:52:47,840
So I went through and gframes wood
is for manually created quads here.

1002
00:52:47,840 --> 00:52:53,540
And then there's four because I also
added the semi broken shapes as well.

1003
00:52:53,540 --> 00:52:55,820
But we don't actually use those.

1004
00:52:55,820 --> 00:53:03,100
But you could decide to turn
these into these on collision,

1005
00:53:03,100 --> 00:53:06,350
perhaps maybe if the velocity isn't
strong enough to break it necessarily,

1006
00:53:06,350 --> 00:53:09,740
but you want to have some sort of
feedback that you collided with it.

1007
00:53:09,740 --> 00:53:15,140
You can just set maybe the frame to
1 or 2 on collision for that object,

1008
00:53:15,140 --> 00:53:18,950
instead of 2 and render
it appropriately.

1009
00:53:18,950 --> 00:53:21,380
But if you're dealing
with a sprite sheet

1010
00:53:21,380 --> 00:53:26,450
and that sprite sheet has odd
distribution of its sprites,

1011
00:53:26,450 --> 00:53:29,480
sometimes you have to figure out
where the offsets are manually

1012
00:53:29,480 --> 00:53:31,190
and do it that way.

1013
00:53:31,190 --> 00:53:34,910
The ideal is that you don't have to and
that you can do it programmatically.

1014
00:53:34,910 --> 00:53:38,270
But it really depends on the
game, what your domain is

1015
00:53:38,270 --> 00:53:42,090
and what objects you're
interacting with in the scene.

1016
00:53:42,090 --> 00:53:44,950
Any questions on the
why or how as to that?

1017
00:53:44,950 --> 00:53:47,700


1018
00:53:47,700 --> 00:53:48,320
Cool.

1019
00:53:48,320 --> 00:53:51,780
So back to the obstacle.

1020
00:53:51,780 --> 00:53:54,020
So they're horizontal or
vertical, and what that does

1021
00:53:54,020 --> 00:53:55,730
is it sets the frame to 2 or 4.

1022
00:53:55,730 --> 00:54:02,180
And the 2 or 4 being in gframes that
would, the 4 quads that I had a hand,

1023
00:54:02,180 --> 00:54:03,620
figure out the coordinates for.

1024
00:54:03,620 --> 00:54:06,350


1025
00:54:06,350 --> 00:54:09,800
And really, it's not a whole
lot different at that point.

1026
00:54:09,800 --> 00:54:15,260
If it's a horizontal
or a vertical shape,

1027
00:54:15,260 --> 00:54:17,690
then we need to set its width
and height appropriately.

1028
00:54:17,690 --> 00:54:19,820
Because it's going to have a different
width and a different height.

1029
00:54:19,820 --> 00:54:22,770
If it's vertical, obviously the
height is higher than the width.

1030
00:54:22,770 --> 00:54:25,910
And if it's horizontal,
the opposite is true.

1031
00:54:25,910 --> 00:54:27,929
But they're both a rectangle shape.

1032
00:54:27,929 --> 00:54:29,720
So you can pass in the
width and the height

1033
00:54:29,720 --> 00:54:32,520
after you calculate that,
and give it the right shape,

1034
00:54:32,520 --> 00:54:33,770
and then ascribe it a fixture.

1035
00:54:33,770 --> 00:54:37,310
And then set user data in this
case, we set user data to obstacle.

1036
00:54:37,310 --> 00:54:40,760
So now that obstacle,
the fixture specifically,

1037
00:54:40,760 --> 00:54:45,080
knows that it's an obstacle, as
opposed to being an alien, as opposed

1038
00:54:45,080 --> 00:54:47,510
to being anything else, as
opposed to being the ground.

1039
00:54:47,510 --> 00:54:54,500
And so when we explore in a few minutes
what the custom collision, world

1040
00:54:54,500 --> 00:54:56,420
collision callbacks,
that we can actually

1041
00:54:56,420 --> 00:54:58,940
define all this interesting
collision behavior for,

1042
00:54:58,940 --> 00:55:01,370
this user data is going to be relevant.

1043
00:55:01,370 --> 00:55:08,310
And then we render it just like
we render the alien as before.

1044
00:55:08,310 --> 00:55:10,875
So any questions on obstacles
and aliens, how they differ,

1045
00:55:10,875 --> 00:55:11,750
how they're the same?

1046
00:55:11,750 --> 00:55:14,588


1047
00:55:14,588 --> 00:55:15,750
Cool.

1048
00:55:15,750 --> 00:55:16,250
All right.

1049
00:55:16,250 --> 00:55:18,500
Let's take a five minute now.

1050
00:55:18,500 --> 00:55:21,710
When we get back, we're going to
actually look at the play state.

1051
00:55:21,710 --> 00:55:23,870
We're going to look
at what makes a level.

1052
00:55:23,870 --> 00:55:27,650
And we're going to actually look
at how we can customize the world

1053
00:55:27,650 --> 00:55:32,480
to resolve collisions in ways that
are relevant to our game behavior.

1054
00:55:32,480 --> 00:55:36,080
As in, how to make things break
when we collide with them,

1055
00:55:36,080 --> 00:55:40,310
how to make the victory screen pop
up when we've destroyed the bird,

1056
00:55:40,310 --> 00:55:41,240
so on and so forth.

1057
00:55:41,240 --> 00:55:43,971


1058
00:55:43,971 --> 00:55:44,470
All right.

1059
00:55:44,470 --> 00:55:45,250
Welcome back.

1060
00:55:45,250 --> 00:55:47,110
So before we took a
break, we were talking

1061
00:55:47,110 --> 00:55:51,120
about the aliens and
obstacles that are in our game

1062
00:55:51,120 --> 00:55:52,880
world that interact with each other.

1063
00:55:52,880 --> 00:55:58,900
They are the backbone of what makes
our games slash Angry Birds work.

1064
00:55:58,900 --> 00:56:02,170
You throw aliens into the
obstacles, obstacles break,

1065
00:56:02,170 --> 00:56:07,660
the bad pigs slash aliens die
and then you score points.

1066
00:56:07,660 --> 00:56:10,120
But we actually have to
model these interactions

1067
00:56:10,120 --> 00:56:13,030
and we have to tell our
game, our world, what

1068
00:56:13,030 --> 00:56:16,900
to do when these collisions happen
in order for things more interesting

1069
00:56:16,900 --> 00:56:19,354
than just things bouncing
off each other to work.

1070
00:56:19,354 --> 00:56:20,520
That's the default behavior.

1071
00:56:20,520 --> 00:56:26,230
Box2D's goal, by default,
is when two things overlap,

1072
00:56:26,230 --> 00:56:29,170
assuming that they're dynamic or
at least one of them is dynamic,

1073
00:56:29,170 --> 00:56:34,840
is to push the dynamic bodies
away until they no longer overlap

1074
00:56:34,840 --> 00:56:38,950
via either position or rotation.

1075
00:56:38,950 --> 00:56:42,640
But that's not the gist
or the goal of our game.

1076
00:56:42,640 --> 00:56:45,490
Because what we want to have
happen is different things happen

1077
00:56:45,490 --> 00:56:49,330
and certain things to disappear and
to break and all sorts of other things

1078
00:56:49,330 --> 00:56:52,210
to happen when different
kinds of objects

1079
00:56:52,210 --> 00:56:56,290
interact with different kinds
of objects at differing speeds.

1080
00:56:56,290 --> 00:57:00,790
So in order to do this, we need
to define collision callbacks

1081
00:57:00,790 --> 00:57:01,630
for our world.

1082
00:57:01,630 --> 00:57:04,810
So a callback, recall,
is a function that gets

1083
00:57:04,810 --> 00:57:06,850
called back when something happens.

1084
00:57:06,850 --> 00:57:12,950
It's just something that will get
called at a specific time or later on.

1085
00:57:12,950 --> 00:57:16,090
And we can define these
callbacks for our world

1086
00:57:16,090 --> 00:57:19,210
such that when two things
collide with each other,

1087
00:57:19,210 --> 00:57:23,350
it will execute this call back and
then perform the corresponding logic

1088
00:57:23,350 --> 00:57:25,750
that we've defined therein.

1089
00:57:25,750 --> 00:57:30,850
And with every collision in Box2D, there
are four callbacks that take place.

1090
00:57:30,850 --> 00:57:35,770
There's begin contact, so when
two things begin to overlap

1091
00:57:35,770 --> 00:57:37,630
or begin to contact one another.

1092
00:57:37,630 --> 00:57:40,480
End contact, so once that
ends, once two objects

1093
00:57:40,480 --> 00:57:42,990
are pushed away from each other.

1094
00:57:42,990 --> 00:57:46,270
Presolved, which happens right
before the collision actually gets

1095
00:57:46,270 --> 00:57:50,200
solved in Box2D, meaning that the
things get pushed away from each other.

1096
00:57:50,200 --> 00:57:54,130
And then postsolved, meaning right after
they get pushed away from each other.

1097
00:57:54,130 --> 00:57:58,040
And the postsolved in
particular is interesting

1098
00:57:58,040 --> 00:58:02,540
because it gets the information about
how the collision needed to resolve.

1099
00:58:02,540 --> 00:58:08,650
So how much velocity or rotation needed
to happen within that interaction.

1100
00:58:08,650 --> 00:58:12,340
And we will not be using end
contact, presolve, or postsolve.

1101
00:58:12,340 --> 00:58:15,370
We will only be using begin
contact because, really, that's

1102
00:58:15,370 --> 00:58:18,612
all we need in order to model the
behavior that we're looking for.

1103
00:58:18,612 --> 00:58:20,320
Because anything that
happens in our game

1104
00:58:20,320 --> 00:58:23,170
we can just figure it out as soon
as two objects touch each other.

1105
00:58:23,170 --> 00:58:25,730


1106
00:58:25,730 --> 00:58:28,600
And these are things, if you're
interested in a tutorial that

1107
00:58:28,600 --> 00:58:31,420
goes over these in perhaps
a little bit more detail,

1108
00:58:31,420 --> 00:58:33,520
there's a link here in the slides.

1109
00:58:33,520 --> 00:58:38,470
But I'll show you how to actually
implement these callbacks yourself.

1110
00:58:38,470 --> 00:58:42,040
You do this via a function
called world set callbacks,

1111
00:58:42,040 --> 00:58:45,110
in this case, F1, F2, F3, F4.

1112
00:58:45,110 --> 00:58:47,770
And recall, because Lua is a
dynamic language where functions

1113
00:58:47,770 --> 00:58:52,210
are first class objects, you can
pass in functions as arguments

1114
00:58:52,210 --> 00:58:53,300
to other functions.

1115
00:58:53,300 --> 00:58:54,260
And that's what we're doing here.

1116
00:58:54,260 --> 00:58:56,218
So this is assuming that
we have four functions

1117
00:58:56,218 --> 00:59:00,820
we've defined called begin contact,
end contact. presolve, or postsolve.

1118
00:59:00,820 --> 00:59:03,250
Their actual names don't matter at all.

1119
00:59:03,250 --> 00:59:05,881
These are just the de
facto names for them.

1120
00:59:05,881 --> 00:59:09,130
What matters is that you have the logic
there and you pass in function objects

1121
00:59:09,130 --> 00:59:11,170
that perform something.

1122
00:59:11,170 --> 00:59:15,130
And you can pass in all empty functions
and Box2D will still behave as normal.

1123
00:59:15,130 --> 00:59:20,680
These are only for when you want more
complicated behavior out of your game

1124
00:59:20,680 --> 00:59:23,320
than just things bouncing
off of each other

1125
00:59:23,320 --> 00:59:26,200
and moving relative to one another.

1126
00:59:26,200 --> 00:59:29,620
So does that make sense?

1127
00:59:29,620 --> 00:59:32,020
So we'll see how this actually works.

1128
00:59:32,020 --> 00:59:34,390
We're going to go ahead
and open up level dot Lua.

1129
00:59:34,390 --> 00:59:37,090
So level dot Lua is a
container class that

1130
00:59:37,090 --> 00:59:40,120
basically has our game
level in it, including

1131
00:59:40,120 --> 00:59:42,430
the world and all the entities.

1132
00:59:42,430 --> 00:59:47,391
And we update it and are
able to model, effectively,

1133
00:59:47,391 --> 00:59:48,640
like a level from Angry Birds.

1134
00:59:48,640 --> 00:59:50,080
That's really what it is.

1135
00:59:50,080 --> 00:59:51,220
It has a world.

1136
00:59:51,220 --> 00:59:55,720
So the level has its own world with 300
positive Y gravity, as we saw before.

1137
00:59:55,720 --> 00:59:58,630
It has a table called destroyed bodies.

1138
00:59:58,630 --> 01:00:01,160
And we'll see that in a second.

1139
01:00:01,160 --> 01:00:02,710
And then here we have four functions.

1140
01:00:02,710 --> 01:00:06,730
Starting on line 22, we have begin
contact, which is a long function.

1141
01:00:06,730 --> 01:00:09,510
And then we have end contact,
presolve, and postsolve.

1142
01:00:09,510 --> 01:00:11,590
Those are the four
callback functions that I

1143
01:00:11,590 --> 01:00:14,659
alluded to just a few seconds ago.

1144
01:00:14,659 --> 01:00:16,450
They take in slightly
different signatures.

1145
01:00:16,450 --> 01:00:19,150
The first three take
A, B, and collision.

1146
01:00:19,150 --> 01:00:23,260
And then the last one takes in A, B,
collision, and then a normal impulse

1147
01:00:23,260 --> 01:00:26,680
and a tangent impulse, which are the
forces that it needed to apply in order

1148
01:00:26,680 --> 01:00:29,620
to push apart the two objects.

1149
01:00:29,620 --> 01:00:31,840
Like I said, we won't be
using these three functions.

1150
01:00:31,840 --> 01:00:36,550
But there might be a situation where
you need to use those functions.

1151
01:00:36,550 --> 01:00:40,330
Maybe you want end contact because,
in your game, two objects attached

1152
01:00:40,330 --> 01:00:43,640
to one another, when they collide
maybe they're magnetic or something,

1153
01:00:43,640 --> 01:00:46,550
and then once they pull apart
maybe you want a particle effect

1154
01:00:46,550 --> 01:00:50,690
or something to show that
they've separated or something.

1155
01:00:50,690 --> 01:00:52,310
And then presolve and postsolve.

1156
01:00:52,310 --> 01:00:54,980
Presolve, offhand I can't
think of a use case,

1157
01:00:54,980 --> 01:00:59,360
but postsolve could be useful
for, depending on your game,

1158
01:00:59,360 --> 01:01:03,552
whether you need to just figure
out maybe the amount of force

1159
01:01:03,552 --> 01:01:04,760
that they needed to separate.

1160
01:01:04,760 --> 01:01:11,540
Maybe you multiply that by some amount
and cause some sort of dramatic effect.

1161
01:01:11,540 --> 01:01:14,120
Those are ultimately dependent
on the domain of your game.

1162
01:01:14,120 --> 01:01:16,120
The important function
that we'll be using today

1163
01:01:16,120 --> 01:01:18,830
is the first one, begin contact.

1164
01:01:18,830 --> 01:01:21,050
And notice, that we've
defined these four functions,

1165
01:01:21,050 --> 01:01:23,460
even if these three are just empty.

1166
01:01:23,460 --> 01:01:27,080
But we pass in, as I said
before, the set callbacks

1167
01:01:27,080 --> 01:01:29,510
function takes in those four functions.

1168
01:01:29,510 --> 01:01:33,410
And notice another interesting thing,
because of Lua's dynamic nature, line

1169
01:01:33,410 --> 01:01:35,330
11 you can see that we
have level init, which

1170
01:01:35,330 --> 01:01:37,820
is the constructor for our level class.

1171
01:01:37,820 --> 01:01:41,060
Within the constructor we
are defining more functions.

1172
01:01:41,060 --> 01:01:45,020
You can define functions as
many layers deep as you want to.

1173
01:01:45,020 --> 01:01:47,690
And you can even return
functions from functions, which

1174
01:01:47,690 --> 01:01:50,959
are called higher order functions.

1175
01:01:50,959 --> 01:01:52,250
Really do whatever you want to.

1176
01:01:52,250 --> 01:01:55,730
In this case we're just defining
the collision callbacks here inside

1177
01:01:55,730 --> 01:01:56,321
of our init.

1178
01:01:56,321 --> 01:01:58,320
But you could put the
most anywhere you want to.

1179
01:01:58,320 --> 01:02:01,370
You can have them outside of the class,
you can have them wherever you want.

1180
01:02:01,370 --> 01:02:03,828
You can have them be global
functions in your main dot Lua,

1181
01:02:03,828 --> 01:02:05,660
which I don't know
how I feel about that.

1182
01:02:05,660 --> 01:02:08,930
But you can do whatever you want
to as long as the functions exist

1183
01:02:08,930 --> 01:02:11,180
and you can reference their
symbols, you can pass them

1184
01:02:11,180 --> 01:02:14,540
into self dot world set callbacks.

1185
01:02:14,540 --> 01:02:19,490
And now, whenever a collision
happens in the world period,

1186
01:02:19,490 --> 01:02:22,640
it's going to call all
four of those functions

1187
01:02:22,640 --> 01:02:26,040
at each stage of each collision.

1188
01:02:26,040 --> 01:02:29,960
So you could see that
potentially getting a little bit

1189
01:02:29,960 --> 01:02:33,810
hairy if you were to scale high
enough with all of your logic.

1190
01:02:33,810 --> 01:02:36,100
If you had a million lines
of code in each of these

1191
01:02:36,100 --> 01:02:38,796
and its executing million
lines of code per collision,

1192
01:02:38,796 --> 01:02:39,920
you could run into trouble.

1193
01:02:39,920 --> 01:02:43,910
But, fortunately, we're not
going anywhere near that.

1194
01:02:43,910 --> 01:02:49,100
The gist of begin contact, so it
takes in an A and a B and a collision.

1195
01:02:49,100 --> 01:02:53,100
We don't end up using the collision
itself, we just use the A and the B

1196
01:02:53,100 --> 01:02:56,060
because that's all we
need for our game world.

1197
01:02:56,060 --> 01:02:58,868
The A and the B are what?

1198
01:02:58,868 --> 01:03:00,368
Do we know what the A and the B are?

1199
01:03:00,368 --> 01:03:02,000
AUDIENCE: Probably the
two objects [INAUDIBLE]..

1200
01:03:02,000 --> 01:03:02,810
COLTON OGDEN: The two objects.

1201
01:03:02,810 --> 01:03:04,685
Do you know whether it's
a body or a fixture?

1202
01:03:04,685 --> 01:03:08,749


1203
01:03:08,749 --> 01:03:10,040
AUDIENCE: It would the fixture.

1204
01:03:10,040 --> 01:03:11,623
COLTON OGDEN: It would be the fixture.

1205
01:03:11,623 --> 01:03:14,640
The fixtures collide with
each other, not the bodies.

1206
01:03:14,640 --> 01:03:18,420
So when you have a body, recall that the
fixture attaches the shape to a body.

1207
01:03:18,420 --> 01:03:22,830
The body is just a position and velocity
container for a bunch of fixtures,

1208
01:03:22,830 --> 01:03:24,150
the body is.

1209
01:03:24,150 --> 01:03:27,810
Each individual fixture
collides with other things,

1210
01:03:27,810 --> 01:03:30,150
other fixtures in your game world.

1211
01:03:30,150 --> 01:03:33,700
And so, recall that
before we had fixture

1212
01:03:33,700 --> 01:03:36,480
set user data because
that's what we ended up

1213
01:03:36,480 --> 01:03:39,720
needing to have data on
when we do the collisions.

1214
01:03:39,720 --> 01:03:43,650
We check to see via get
user data what something is

1215
01:03:43,650 --> 01:03:46,230
or what metadata we've
given to that fixture.

1216
01:03:46,230 --> 01:03:51,690
And then we can then separate
different classes of objects this way.

1217
01:03:51,690 --> 01:03:55,630
We can say, oh, this object was an
alien, or this object was an obstacle,

1218
01:03:55,630 --> 01:03:56,880
or this object was the ground.

1219
01:03:56,880 --> 01:03:59,129
And then we can say, oh, did
we collide with an alien?

1220
01:03:59,129 --> 01:04:01,830
Was the collision between
an alien and the ground?

1221
01:04:01,830 --> 01:04:04,620
If it was, OK, let's play
a bounce sound effect.

1222
01:04:04,620 --> 01:04:07,230
And if it was between an alien
and the other alien, the player

1223
01:04:07,230 --> 01:04:10,170
and the other alien, and the
velocity was fast enough,

1224
01:04:10,170 --> 01:04:11,820
OK, the alien should die.

1225
01:04:11,820 --> 01:04:12,420
Right?

1226
01:04:12,420 --> 01:04:15,810
We can do arbitrary things.

1227
01:04:15,810 --> 01:04:19,320
And so the way that I've
programmed it here such that we

1228
01:04:19,320 --> 01:04:21,870
can see what two things
interacted with each other,

1229
01:04:21,870 --> 01:04:26,280
and this is a very
simple use of user data.

1230
01:04:26,280 --> 01:04:31,020
All we we're doing in this code base
is just assigning strings to fixtures,

1231
01:04:31,020 --> 01:04:34,770
but you could assign tables to
fixtures with arbitrary amounts of data

1232
01:04:34,770 --> 01:04:36,780
and do all sorts of things.

1233
01:04:36,780 --> 01:04:39,120
In this case, we're only using strings.

1234
01:04:39,120 --> 01:04:42,960
So I create a table, an
empty table, and then I just

1235
01:04:42,960 --> 01:04:47,490
assign at table, at that string, true.

1236
01:04:47,490 --> 01:04:49,360
And then I can just query that table.

1237
01:04:49,360 --> 01:04:52,200
Do I have a key player and a key alien?

1238
01:04:52,200 --> 01:04:56,324
Do I have a key obstacle
and a key obstacle?

1239
01:04:56,324 --> 01:04:58,740
This is how you can figure out
what your two objects were.

1240
01:04:58,740 --> 01:05:02,242
Because A could be a player
and B can be an obstacle.

1241
01:05:02,242 --> 01:05:04,200
A can be an obstacle and
B could be the player.

1242
01:05:04,200 --> 01:05:08,050
So you have to take both
of that into consideration.

1243
01:05:08,050 --> 01:05:12,990
So it allows us to do if types
obstacle and types player, so

1244
01:05:12,990 --> 01:05:20,370
a collision between the player and an
obstacle, if it's fast enough, then we

1245
01:05:20,370 --> 01:05:22,750
can destroy the obstacle.

1246
01:05:22,750 --> 01:05:23,880
This is what we do here.

1247
01:05:23,880 --> 01:05:29,760
So I take the absolute value
of the velocity on the X and Y.

1248
01:05:29,760 --> 01:05:33,790
So I do vel X vel Y gets
the body's linear velocity.

1249
01:05:33,790 --> 01:05:37,220
So linear velocity is just
where it's moving in the world.

1250
01:05:37,220 --> 01:05:42,360
And it returns two values because
velocity has an X and Y component.

1251
01:05:42,360 --> 01:05:48,810
And then we sum it here by taking
its absolute value of both parts

1252
01:05:48,810 --> 01:05:50,230
and adding it together.

1253
01:05:50,230 --> 01:05:54,450
So if it's moving fast on the
x-axis, but not fast on the y-axis,

1254
01:05:54,450 --> 01:05:57,420
or if it's not moving fast on either,
or if it's moving fast on both,

1255
01:05:57,420 --> 01:06:02,220
we have a sense, in general, what's
the average velocity of our object.

1256
01:06:02,220 --> 01:06:04,620
If it's moving fast
on any of the axes, we

1257
01:06:04,620 --> 01:06:08,580
can assume that that's sufficient
force to cause an object

1258
01:06:08,580 --> 01:06:10,500
to get destroyed, right?

1259
01:06:10,500 --> 01:06:14,250
So we do if the velocity is greater
than 20, just an arbitrary value

1260
01:06:14,250 --> 01:06:16,680
that I came up with
that seemed appropriate,

1261
01:06:16,680 --> 01:06:19,370
then we're going to do this.

1262
01:06:19,370 --> 01:06:24,280
Table dot insert self dot destroyed
bodies, which we saw earlier.

1263
01:06:24,280 --> 01:06:25,860
And then the obstacles body.

1264
01:06:25,860 --> 01:06:30,030
Now, why are we inserting
that value here as

1265
01:06:30,030 --> 01:06:33,968
opposed to, maybe just destroying
it inside this function?

1266
01:06:33,968 --> 01:06:38,155


1267
01:06:38,155 --> 01:06:39,530
AUDIENCE: Destroying the fixture.

1268
01:06:39,530 --> 01:06:41,080
COLTON OGDEN: Destroying the body.

1269
01:06:41,080 --> 01:06:43,490
The fixture, yeah, in this case.

1270
01:06:43,490 --> 01:06:45,110
AUDIENCE: I mean the fixture, sorry.

1271
01:06:45,110 --> 01:06:47,360
Because you're still referencing
it later in the code.

1272
01:06:47,360 --> 01:06:49,735
COLTON OGDEN: You're still
referencing later in the code.

1273
01:06:49,735 --> 01:06:52,070
Box2D maintains a reference
to all of the bodies, all

1274
01:06:52,070 --> 01:06:58,820
of the fixtures in your
world, regardless of

1275
01:06:58,820 --> 01:07:00,440
whether you've deleted them or not.

1276
01:07:00,440 --> 01:07:03,470
But if you delete them while
it's in the middle of a,

1277
01:07:03,470 --> 01:07:06,950
like checking for collision,
it'll try to do another collision

1278
01:07:06,950 --> 01:07:12,100
with that destroyed body and you'll
get a crash or a stack overflow error.

1279
01:07:12,100 --> 01:07:14,300
I found I experienced both of those.

1280
01:07:14,300 --> 01:07:19,940
You don't want to ever delete or destroy
anything while inside a collision

1281
01:07:19,940 --> 01:07:21,260
callback for your world.

1282
01:07:21,260 --> 01:07:24,192
It will cause horrible things to happen.

1283
01:07:24,192 --> 01:07:26,900
So what we do is we maintain a
reference to everything that we're

1284
01:07:26,900 --> 01:07:29,480
going to destroy by just inserting it.

1285
01:07:29,480 --> 01:07:37,220
So if we do table dot insert the body of
whatever we want into destroyed bodies,

1286
01:07:37,220 --> 01:07:40,250
we can then loop over that
after the world updates.

1287
01:07:40,250 --> 01:07:45,750
And then just destroy them one by
one outside of the update function.

1288
01:07:45,750 --> 01:07:49,760
And the reason that we are passing
in the body and not the fixture

1289
01:07:49,760 --> 01:07:55,430
is when we destroy a body,
it destroys all the fixtures

1290
01:07:55,430 --> 01:07:57,451
associated with that body as well.

1291
01:07:57,451 --> 01:07:59,700
So we're just destroying the
top level container here.

1292
01:07:59,700 --> 01:08:04,970
In this case, it doesn't matter too much
whether we destroy a fixture or a body

1293
01:08:04,970 --> 01:08:09,090
because it's a one to one relationship.

1294
01:08:09,090 --> 01:08:14,012
But if you had, let's say, a body
that has five fixtures on it.

1295
01:08:14,012 --> 01:08:16,220
And if that entire thing
collides with something else

1296
01:08:16,220 --> 01:08:18,080
and you want to destroy
that entire thing,

1297
01:08:18,080 --> 01:08:20,479
you want to destroy the body,
not an individual fixture.

1298
01:08:20,479 --> 01:08:24,410
Because when you destroy the body, it
destroys all the fixtures, not just

1299
01:08:24,410 --> 01:08:25,760
the one fixture.

1300
01:08:25,760 --> 01:08:29,990
So that's we're deleting the body,
adding the body to destroyed bodies,

1301
01:08:29,990 --> 01:08:34,189
and then later performing
a delete off of that.

1302
01:08:34,189 --> 01:08:39,740
The function is destroy here.

1303
01:08:39,740 --> 01:08:42,350
So on line 157--

1304
01:08:42,350 --> 01:08:45,859
well, 155 to 159, this
is where we actually

1305
01:08:45,859 --> 01:08:48,310
iterate over everything
that we wanted to flag,

1306
01:08:48,310 --> 01:08:51,560
or that we've flagged as
destroyed, and we destroy it.

1307
01:08:51,560 --> 01:08:55,910
So if not body is destroyed, destroy it.

1308
01:08:55,910 --> 01:09:01,790
And then once we destroy it, we're
going to go down here and end up

1309
01:09:01,790 --> 01:09:05,420
actually removing the
obstacle and the alien class

1310
01:09:05,420 --> 01:09:09,410
from our list of aliens and obstacles.

1311
01:09:09,410 --> 01:09:12,479
Because that maintains a
reference to what we're drawing

1312
01:09:12,479 --> 01:09:13,979
and we want to also delete that.

1313
01:09:13,979 --> 01:09:17,450
So not only do we want to delete
the object from the world,

1314
01:09:17,450 --> 01:09:19,970
we want to delete the
objects that we've created

1315
01:09:19,970 --> 01:09:23,090
that are a wrapper for
the bodies and fixtures

1316
01:09:23,090 --> 01:09:26,540
and also the drawing of our aliens so
it no longer gets drawn to the scene,

1317
01:09:26,540 --> 01:09:27,388
basically.

1318
01:09:27,388 --> 01:09:30,020


1319
01:09:30,020 --> 01:09:36,410
So yeah, don't ever delete a body
or a fixture inside your callbacks.

1320
01:09:36,410 --> 01:09:39,109
Always flag them and
delete them afterwards.

1321
01:09:39,109 --> 01:09:43,700
Basically, don't delete in the
middle of a world update function

1322
01:09:43,700 --> 01:09:45,410
call, which we see here.

1323
01:09:45,410 --> 01:09:49,550
Notice that this takes place,
152, were doing self world update.

1324
01:09:49,550 --> 01:09:55,850
And then on 155 to 159, we've populated
destroyed bodies via the collision

1325
01:09:55,850 --> 01:09:57,780
callback that we defined up above.

1326
01:09:57,780 --> 01:10:00,650
So in here, this is where we
can actually destroy everything.

1327
01:10:00,650 --> 01:10:04,920
This is outside of the update function,
here, the world update function.

1328
01:10:04,920 --> 01:10:08,210
We don't need to worry about stack
overflow or a segfault, which

1329
01:10:08,210 --> 01:10:13,070
we get by deleting something
while it's in the middle

1330
01:10:13,070 --> 01:10:16,280
of processing its collisions.

1331
01:10:16,280 --> 01:10:17,390
So unfortunate bug.

1332
01:10:17,390 --> 01:10:21,620
If you ever find yourself running
into stack overflows or segfaults

1333
01:10:21,620 --> 01:10:25,680
in your collision callbacks, make
sure you're not deleting anything.

1334
01:10:25,680 --> 01:10:28,430
But we can see here, it's
very similar, the behavior

1335
01:10:28,430 --> 01:10:32,960
we defined between obstacles and the
player, between obstacles and aliens,

1336
01:10:32,960 --> 01:10:34,940
and between the player and alien.

1337
01:10:34,940 --> 01:10:38,480
Ultimately, it's check to see
whether the average of its velocity

1338
01:10:38,480 --> 01:10:41,000
is greater than a certain
number, in this case, 20.

1339
01:10:41,000 --> 01:10:44,627
And if it is, flag it as destroyed.

1340
01:10:44,627 --> 01:10:46,460
So if the player hits
the alien, destroy it.

1341
01:10:46,460 --> 01:10:48,560
If a obstacle hits
the alien, destroy it.

1342
01:10:48,560 --> 01:10:51,230
And it's similar to how
it works in Angry Birds.

1343
01:10:51,230 --> 01:10:57,020
When you throw something at a structure
in Angry Birds and a piece of debris

1344
01:10:57,020 --> 01:11:00,740
falls off of it and hits the
pig, usually kills the pig too.

1345
01:11:00,740 --> 01:11:04,331
And if your bird hits the pig,
that usually kills the pig.

1346
01:11:04,331 --> 01:11:06,830
But if you're not moving fast
enough or if a piece of debris

1347
01:11:06,830 --> 01:11:09,530
isn't moving fast enough,
it'll just nudge the pig,

1348
01:11:09,530 --> 01:11:11,000
it won't actually kill the pig.

1349
01:11:11,000 --> 01:11:13,820
So that's why we're taking all
of this into consideration.

1350
01:11:13,820 --> 01:11:18,780
We're not just doing a blind delete
off of the body's in our code,

1351
01:11:18,780 --> 01:11:22,540
we're actually making sure, is
it also moving fast enough, i.e.

1352
01:11:22,540 --> 01:11:24,170
does it have enough force?

1353
01:11:24,170 --> 01:11:28,890
And if it does, then perform the code,
then perform the deletion or flag it

1354
01:11:28,890 --> 01:11:30,210
as being deleted.

1355
01:11:30,210 --> 01:11:33,110
And so once again, that's
why user data is important.

1356
01:11:33,110 --> 01:11:37,920
Because that's how we're able to--
because notice in the callback

1357
01:11:37,920 --> 01:11:41,820
we just get an A and a B. And those
are always going to be fixtures.

1358
01:11:41,820 --> 01:11:44,520
Fixtures, in order for it to
know what kind of a fixture

1359
01:11:44,520 --> 01:11:48,000
it is, whether it belongs
to a player or an alien,

1360
01:11:48,000 --> 01:11:50,010
we need to give it some information.

1361
01:11:50,010 --> 01:11:55,090
So the set user data flags the
fixtures as being of a specific type.

1362
01:11:55,090 --> 01:11:58,170
And then we can fetch it
here with get user data

1363
01:11:58,170 --> 01:12:02,490
and then actually perform
the relevant game logic.

1364
01:12:02,490 --> 01:12:05,424
Any questions as to how this works?

1365
01:12:05,424 --> 01:12:11,412
AUDIENCE: Are you checking for if
two obstacles knock into each other?

1366
01:12:11,412 --> 01:12:14,370
COLTON OGDEN: Am I checking with two
obstacles collide with each other?

1367
01:12:14,370 --> 01:12:15,570
I might not be.

1368
01:12:15,570 --> 01:12:18,720
In that case-- you should.

1369
01:12:18,720 --> 01:12:21,930
In that case, since we're not,
they'll just bump into each other.

1370
01:12:21,930 --> 01:12:24,780
But, yeah, if we wanted
two wooden obstacles

1371
01:12:24,780 --> 01:12:27,240
to destroy each other
if they hit fast enough,

1372
01:12:27,240 --> 01:12:29,340
you would just do the same thing here.

1373
01:12:29,340 --> 01:12:32,850
If types obstacle, I guess.

1374
01:12:32,850 --> 01:12:35,490
But in this case, because
they're both the same key,

1375
01:12:35,490 --> 01:12:39,342
you would have to do if types--

1376
01:12:39,342 --> 01:12:40,800
let's see how we're doing it again.

1377
01:12:40,800 --> 01:12:45,310
So types obstacles is true,
types obstacles is true.

1378
01:12:45,310 --> 01:12:50,740
You would say if types obstacle and not
types alien, not types player, not--

1379
01:12:50,740 --> 01:12:52,300
there's a cleaner way to do it.

1380
01:12:52,300 --> 01:12:54,390
AUDIENCE: Like a series
of [INAUDIBLE] statements.

1381
01:12:54,390 --> 01:12:54,630
COLTON OGDEN: Yeah.

1382
01:12:54,630 --> 01:12:55,800
AUDIENCE: [INAUDIBLE] statements.

1383
01:12:55,800 --> 01:12:56,591
COLTON OGDEN: Yeah.

1384
01:12:56,591 --> 01:12:57,330
That's true.

1385
01:12:57,330 --> 01:12:59,680
Yeah, there's a lot of ways.

1386
01:12:59,680 --> 01:13:02,702
And if I were to re-engineer this,
I would also abstract out this code

1387
01:13:02,702 --> 01:13:03,660
and make it a function.

1388
01:13:03,660 --> 01:13:07,620
Because it's pretty much the same
code between all three of these.

1389
01:13:07,620 --> 01:13:09,630
But just to illustrate
and just for simplicity

1390
01:13:09,630 --> 01:13:12,080
because it's pretty
similar interactions,

1391
01:13:12,080 --> 01:13:15,420
didn't really put too much
engineering forethought into it.

1392
01:13:15,420 --> 01:13:20,580
Definitely if you expand upon
it, I would recommend doing that.

1393
01:13:20,580 --> 01:13:26,070
But that's the gist of making our
world behave beyond just resolving

1394
01:13:26,070 --> 01:13:28,620
collisions and pushing obstacles
away from each other, which

1395
01:13:28,620 --> 01:13:31,690
is the default behavior.

1396
01:13:31,690 --> 01:13:33,090
So we set the callbacks.

1397
01:13:33,090 --> 01:13:33,630
We're good.

1398
01:13:33,630 --> 01:13:36,671
Now things, when we interact with each
other, they'll behave differently,

1399
01:13:36,671 --> 01:13:39,210
they'll trigger different behavior.

1400
01:13:39,210 --> 01:13:42,270
We have this thing called a launch
marker, an alien launch marker.

1401
01:13:42,270 --> 01:13:43,711
Anybody know what that might be?

1402
01:13:43,711 --> 01:13:47,559


1403
01:13:47,559 --> 01:13:50,697
AUDIENCE: Is that the little
dots that show the trajectory?

1404
01:13:50,697 --> 01:13:53,280
COLTON OGDEN: Yeah, so it's the
dots that show the trajectory.

1405
01:13:53,280 --> 01:13:56,220
It's one, the alien being rendered
on the left side of the screen

1406
01:13:56,220 --> 01:14:00,180
without any physics applied to
it, that's click and dragable.

1407
01:14:00,180 --> 01:14:02,040
And it also renders a trajectory.

1408
01:14:02,040 --> 01:14:07,050
And when you release the mouse,
it launches an actual Box2D alien

1409
01:14:07,050 --> 01:14:12,630
traveling in the direction
that that trajectory foretells.

1410
01:14:12,630 --> 01:14:19,024
If we look at alien launch marker here,
it basically maintains a reference to

1411
01:14:19,024 --> 01:14:20,190
whether we're aiming or not.

1412
01:14:20,190 --> 01:14:21,600
So it's got a couple of states.

1413
01:14:21,600 --> 01:14:25,190
It's got a launch state
and an aiming state.

1414
01:14:25,190 --> 01:14:27,960
An alien that we'll have a
reference to eventually, which

1415
01:14:27,960 --> 01:14:30,400
will spawn and will give it an impulse.

1416
01:14:30,400 --> 01:14:36,420
So an impulse is effectively setting
its velocity immediately to some value,

1417
01:14:36,420 --> 01:14:38,160
as opposed to something over time.

1418
01:14:38,160 --> 01:14:40,170
We can apply force to
an object, which would

1419
01:14:40,170 --> 01:14:43,230
be like you driving your
car up against something

1420
01:14:43,230 --> 01:14:46,110
and then gradually accelerating,
that's applying force.

1421
01:14:46,110 --> 01:14:49,920
And we can also apply impulse
by going full speed with our car

1422
01:14:49,920 --> 01:14:52,230
and hitting an object,
and that will have

1423
01:14:52,230 --> 01:14:56,220
the effect of applying an
impulse at a certain velocity.

1424
01:14:56,220 --> 01:15:00,450
When we drag our alien
and then we release it,

1425
01:15:00,450 --> 01:15:03,480
we want to apply an impulse in the
opposite direction of where we're

1426
01:15:03,480 --> 01:15:06,060
dragging based on a certain amount.

1427
01:15:06,060 --> 01:15:10,500
I scaled it by 10, but you
can have it be arbitrary.

1428
01:15:10,500 --> 01:15:14,550
And then the trajectory
models where it's going.

1429
01:15:14,550 --> 01:15:20,110
And the trajectory is
calculated via these lines here.

1430
01:15:20,110 --> 01:15:22,250
So from line 90 to 104.

1431
01:15:22,250 --> 01:15:25,620
There is a formula
for, in that Box2D set

1432
01:15:25,620 --> 01:15:27,390
of tutorials, that
actually shows you how

1433
01:15:27,390 --> 01:15:31,890
to calculate an estimated trajectory
given a starting impulse and a starting

1434
01:15:31,890 --> 01:15:33,900
position.

1435
01:15:33,900 --> 01:15:36,060
Which is this formula here.

1436
01:15:36,060 --> 01:15:38,190
It's semi-complicated.

1437
01:15:38,190 --> 01:15:40,500
The article goes into
detail as to how it works,

1438
01:15:40,500 --> 01:15:45,420
but it effectively
calculates 1/60 of a second,

1439
01:15:45,420 --> 01:15:48,580
assuming that we're running our
simulation at 1/60 of a second,

1440
01:15:48,580 --> 01:15:52,810
it will, over 90
iterations here, 1 to 90,

1441
01:15:52,810 --> 01:15:56,310
calculate each individual
step of that simulation.

1442
01:15:56,310 --> 01:15:58,900
And then I only render every 5 here.

1443
01:15:58,900 --> 01:16:03,180
So if i is mod 5 s 0,
then I'll actually end up

1444
01:16:03,180 --> 01:16:05,640
drawing a circle at
trajectory X, trajectory

1445
01:16:05,640 --> 01:16:07,830
Y. Trajectory X and Y being here.

1446
01:16:07,830 --> 01:16:10,950
Shifted X, shifted Y being
the starting location.

1447
01:16:10,950 --> 01:16:15,180
And then we multiply i by 1/60
of a second, which will give us

1448
01:16:15,180 --> 01:16:19,860
the scalar for this impulse here.

1449
01:16:19,860 --> 01:16:23,600
And then with gravity we have
to do this i squared plus

1450
01:16:23,600 --> 01:16:31,530
i times 1/2 times the gravity on
the y-axis times 1/60 squared.

1451
01:16:31,530 --> 01:16:34,530
The article goes into a little bit
more detail as to how it works.

1452
01:16:34,530 --> 01:16:38,910
But that's it converted
into source code.

1453
01:16:38,910 --> 01:16:41,010
But it's effectively
a gravity simulation

1454
01:16:41,010 --> 01:16:44,490
and a velocity simulation over time.

1455
01:16:44,490 --> 01:16:47,670
And by rendering it based
on 90 iterations, which

1456
01:16:47,670 --> 01:16:51,210
is one and a half seconds,
at 1/60 of a second

1457
01:16:51,210 --> 01:16:54,750
we can forecast where
exactly we're going.

1458
01:16:54,750 --> 01:17:00,620
And then when we apply this impulse, X
and Y, the ball will actually travel,

1459
01:17:00,620 --> 01:17:04,690
the alien will actually travel in that
direction at that exact trajectory.

1460
01:17:04,690 --> 01:17:09,050


1461
01:17:09,050 --> 01:17:12,050
That's the complicated
part of the launch marker.

1462
01:17:12,050 --> 01:17:16,550
The other part is that it has a
couple of states, like I said before.

1463
01:17:16,550 --> 01:17:20,180
So when we click and we're not
launched, it should go into aiming mode.

1464
01:17:20,180 --> 01:17:25,790
And so if we're aiming then we're
going to set a rotation to--

1465
01:17:25,790 --> 01:17:31,610
actually, rotation is not relevant
because this was before I ended up

1466
01:17:31,610 --> 01:17:34,760
using the predictive trajectory method.

1467
01:17:34,760 --> 01:17:39,470
The shift at X and Y though, those are
relevant because that's the starting

1468
01:17:39,470 --> 01:17:41,240
location for your trajectory.

1469
01:17:41,240 --> 01:17:43,084
That's wherever your mouse is.

1470
01:17:43,084 --> 01:17:45,500
And we clamp it so that it
doesn't go past a certain limit

1471
01:17:45,500 --> 01:17:49,730
on the left or the right, so
that it stays within a box area.

1472
01:17:49,730 --> 01:17:52,160
But this will be whenever
you let go of the mouse, that

1473
01:17:52,160 --> 01:17:55,670
will be where we spawn
the Box2D alien and apply

1474
01:17:55,670 --> 01:17:59,460
an impulse in a negative direction
relative to where we move the mouse.

1475
01:17:59,460 --> 01:18:01,820
So if we move the mouse
to the left and down,

1476
01:18:01,820 --> 01:18:05,620
it's going to negate that
with an impulse going up

1477
01:18:05,620 --> 01:18:08,330
and to the right, if that makes sense.

1478
01:18:08,330 --> 01:18:10,378
And that's what's shown
by the trajectory.

1479
01:18:10,378 --> 01:18:13,130


1480
01:18:13,130 --> 01:18:15,560
And then, aside from that,
it renders different things

1481
01:18:15,560 --> 01:18:16,827
depending on whether or not--

1482
01:18:16,827 --> 01:18:17,660
what state we're in.

1483
01:18:17,660 --> 01:18:20,600
So if we haven't launched, it
will render just the alien.

1484
01:18:20,600 --> 01:18:23,660
If we're in aiming mode then it
should actually render and calculate

1485
01:18:23,660 --> 01:18:24,710
the trajectory.

1486
01:18:24,710 --> 01:18:27,080
Otherwise, it would
just render the alien.

1487
01:18:27,080 --> 01:18:34,130
And so once we release the mouse,
so was released 1 and were aiming,

1488
01:18:34,130 --> 01:18:35,960
launched is true, spawn an alien.

1489
01:18:35,960 --> 01:18:40,610
So we create a new alien
with self world, it's round.

1490
01:18:40,610 --> 01:18:43,400
We started at shifted
X and shifted Y. We

1491
01:18:43,400 --> 01:18:48,720
set its linear velocity to the same
values that we calculated before.

1492
01:18:48,720 --> 01:18:51,960
So it's base X minus shifted X times 10.

1493
01:18:51,960 --> 01:18:53,450
So the times 10 is a scalar amount.

1494
01:18:53,450 --> 01:18:56,450


1495
01:18:56,450 --> 01:19:03,421
And then the base X is where
we've moved it, effectively.

1496
01:19:03,421 --> 01:19:03,920
Or, no.

1497
01:19:03,920 --> 01:19:07,970
Base X is where it starts and
shifted X is where we've moved it.

1498
01:19:07,970 --> 01:19:11,390
And so by subtracting
shifted from the base,

1499
01:19:11,390 --> 01:19:16,280
we get the negative direction that
we want to effect the impulse.

1500
01:19:16,280 --> 01:19:21,560
And then the impulse is set
here with linear velocity.

1501
01:19:21,560 --> 01:19:26,660
And then we also set it to
have a restitution of 0.4.

1502
01:19:26,660 --> 01:19:29,420
Recall, restitution is bounciness.

1503
01:19:29,420 --> 01:19:32,450
So our alien bounces a little
bit when it hits the ground.

1504
01:19:32,450 --> 01:19:37,170
And then anybody know what
angular damping might be?

1505
01:19:37,170 --> 01:19:39,680
Any guesses?

1506
01:19:39,680 --> 01:19:45,860
Angular damping is when it rotates,
basically, friction on its rotation.

1507
01:19:45,860 --> 01:19:49,520
So that when it rotates on the
ground, it doesn't roll indefinitely.

1508
01:19:49,520 --> 01:19:52,997
If we don't set that, it'll just roll
forever and ever and ever and ever.

1509
01:19:52,997 --> 01:19:54,080
Which is not what we want.

1510
01:19:54,080 --> 01:19:56,990
We want it to stop at a certain
point because once it stops,

1511
01:19:56,990 --> 01:20:00,170
we know, OK, now we can get
the next alien ready to launch.

1512
01:20:00,170 --> 01:20:03,170


1513
01:20:03,170 --> 01:20:05,420
And that's the gist
behind the launch marker.

1514
01:20:05,420 --> 01:20:07,294
How we render trajectory.

1515
01:20:07,294 --> 01:20:10,460
For the math on that, a little bit more
in detail, I would explore that URL.

1516
01:20:10,460 --> 01:20:12,740
It goes into it into pretty good detail.

1517
01:20:12,740 --> 01:20:18,156
I use that as a reference for
creating this bit of code here.

1518
01:20:18,156 --> 01:20:20,030
But yeah, effectively,
is it's just rendering

1519
01:20:20,030 --> 01:20:24,470
a bunch of circles with that
trajectory and calculating it

1520
01:20:24,470 --> 01:20:30,770
over 90 ticks, 90 frame iterations.

1521
01:20:30,770 --> 01:20:32,860
Back to the level.

1522
01:20:32,860 --> 01:20:37,402
Sorry, any questions overall as
to how the launch marker works?

1523
01:20:37,402 --> 01:20:38,334
AUDIENCE: No.

1524
01:20:38,334 --> 01:20:40,000
COLTON OGDEN: Cool.

1525
01:20:40,000 --> 01:20:40,500
All right.

1526
01:20:40,500 --> 01:20:44,190
So then we have an alien's
table, an obstacles table,

1527
01:20:44,190 --> 01:20:47,580
edge shape for the ground.

1528
01:20:47,580 --> 01:20:50,660
And then we just create
an alien to destroy.

1529
01:20:50,660 --> 01:20:52,140
Spawn a few obstacles here.

1530
01:20:52,140 --> 01:20:56,280
So in this case, two vertical
obstacles and a horizontal one.

1531
01:20:56,280 --> 01:20:59,580
Positioned such that the horizontal
one is over the vertical ones

1532
01:20:59,580 --> 01:21:04,730
and they're spaced apart such that
the aliens are in the middle of them.

1533
01:21:04,730 --> 01:21:08,980
Then the ground here, we give
the ground some friction, 0.5.

1534
01:21:08,980 --> 01:21:12,280
And that's pretty much it
for setting up our level.

1535
01:21:12,280 --> 01:21:18,330
So if we wanted to, after this
point, we have the foundation

1536
01:21:18,330 --> 01:21:24,030
necessary to really spawn arbitrary
levels with admittedly simple obstacles

1537
01:21:24,030 --> 01:21:24,900
at this point.

1538
01:21:24,900 --> 01:21:26,970
But we could set--

1539
01:21:26,970 --> 01:21:30,270
because all we're doing here is
just simple insertions to our aliens

1540
01:21:30,270 --> 01:21:36,030
and obstacles table, we could create
pretty much any level just by, maybe

1541
01:21:36,030 --> 01:21:40,710
in data, specifying level
could be like a table

1542
01:21:40,710 --> 01:21:44,220
and then aliens could be another table.

1543
01:21:44,220 --> 01:21:53,100
And then maybe all it is just
a like X equals some value,

1544
01:21:53,100 --> 01:21:55,170
and then Y equals some value.

1545
01:21:55,170 --> 01:21:59,340
And then obstacles is the same thing.

1546
01:21:59,340 --> 01:22:02,640
And then all we do is just we
iterate over this level definition

1547
01:22:02,640 --> 01:22:07,440
and we just say, new alien
for every table here.

1548
01:22:07,440 --> 01:22:09,390
And then new obstacle
for every table in here.

1549
01:22:09,390 --> 01:22:11,640
And then now your
levels are data driven.

1550
01:22:11,640 --> 01:22:13,260
It's easy just to make levels.

1551
01:22:13,260 --> 01:22:15,134
You don't have to code, really, much.

1552
01:22:15,134 --> 01:22:16,800
And you can put this in a separate file.

1553
01:22:16,800 --> 01:22:21,240
Be like, levels dot Lua, and then
just load individual levels at a time.

1554
01:22:21,240 --> 01:22:28,020
Level 1 equals-- levels would
be the top level container.

1555
01:22:28,020 --> 01:22:33,720
And then you would have 1
equals all of this, and then 2

1556
01:22:33,720 --> 01:22:36,004
equals another one,
3 equals another one.

1557
01:22:36,004 --> 01:22:37,920
And then you're not
really programming as much

1558
01:22:37,920 --> 01:22:40,170
as you are just laying
things out in data.

1559
01:22:40,170 --> 01:22:41,640
Super nice and concise.

1560
01:22:41,640 --> 01:22:44,980
That's a nice thing about a
language like Lua, is that you can,

1561
01:22:44,980 --> 01:22:47,130
and it's the same thing
in JavaScript with JSON,

1562
01:22:47,130 --> 01:22:50,970
you can just define things
as data and then write

1563
01:22:50,970 --> 01:22:54,630
a script to go over it and construct
your actual relevant data structures

1564
01:22:54,630 --> 01:22:55,760
that way--

1565
01:22:55,760 --> 01:22:57,240
in your code that way.

1566
01:22:57,240 --> 01:22:59,580
When you have the
foundation like we have now

1567
01:22:59,580 --> 01:23:02,340
where you can think in terms
of obstacles and aliens,

1568
01:23:02,340 --> 01:23:04,650
you can construct levels like so.

1569
01:23:04,650 --> 01:23:07,170
And obviously you could go a
lot more complicated with this.

1570
01:23:07,170 --> 01:23:14,280
All we're doing is having very simple
almost boring static obstacles.

1571
01:23:14,280 --> 01:23:17,280
They're not static in a technical
sense because they're dynamic objects,

1572
01:23:17,280 --> 01:23:21,520
but all they really do is just
stand there and then fall over.

1573
01:23:21,520 --> 01:23:25,890
But if you wanted a
pulley system or maybe

1574
01:23:25,890 --> 01:23:29,520
something that's shaped in
a giant head or something,

1575
01:23:29,520 --> 01:23:36,880
you can create arbitrarily complex
objects that way using joints.

1576
01:23:36,880 --> 01:23:40,050
And if you're curious, I recommend to
look into the documentation for Love2D

1577
01:23:40,050 --> 01:23:40,980
a little bit more.

1578
01:23:40,980 --> 01:23:44,340
Especially their weld joints
are what you would use

1579
01:23:44,340 --> 01:23:47,970
to combine pieces in arbitrary shapes.

1580
01:23:47,970 --> 01:23:50,820
But you could easily take
this to the next level

1581
01:23:50,820 --> 01:23:56,520
and start to create in that same
level definition, arbitrarily shaped,

1582
01:23:56,520 --> 01:24:01,495
welded together obstacles.

1583
01:24:01,495 --> 01:24:03,870
But that would be, I think,
a next step if you're looking

1584
01:24:03,870 --> 01:24:06,990
to take this beyond just one level.

1585
01:24:06,990 --> 01:24:12,510
I would say, think in terms of, how
can I get my game world represented

1586
01:24:12,510 --> 01:24:14,850
in a very simple data like way?

1587
01:24:14,850 --> 01:24:17,670
Because not only does it make it
easier for you to create content,

1588
01:24:17,670 --> 01:24:20,430
it allows you to shift that
burden to somebody else

1589
01:24:20,430 --> 01:24:23,002
and allow you to give the
task of creating levels

1590
01:24:23,002 --> 01:24:24,960
less to a programmer and
maybe more to somebody

1591
01:24:24,960 --> 01:24:28,290
who has just a design background who
isn't as comfortable writing code.

1592
01:24:28,290 --> 01:24:31,920
And allow you to create the engine that
constructs the game world based off

1593
01:24:31,920 --> 01:24:34,440
of this data.

1594
01:24:34,440 --> 01:24:40,560
Any questions as to how
we've set things up here?

1595
01:24:40,560 --> 01:24:41,877
OK.

1596
01:24:41,877 --> 01:24:43,710
So we have the ground,
we have a background.

1597
01:24:43,710 --> 01:24:47,550
A background is just a simple
class that renders a static image

1598
01:24:47,550 --> 01:24:49,860
that you can scroll the
image with left or right,

1599
01:24:49,860 --> 01:24:51,930
but we don't end up using it much.

1600
01:24:51,930 --> 01:24:55,590
It's relevant in Angry Birds because
in Angry Birds they have a camera,

1601
01:24:55,590 --> 01:25:00,540
and the camera pans left to
right depending on how far away

1602
01:25:00,540 --> 01:25:02,790
the fortress is from your sling shot.

1603
01:25:02,790 --> 01:25:06,660
So that's in there if you want
to experiment with it at all,

1604
01:25:06,660 --> 01:25:08,160
and experiment with a moving camera.

1605
01:25:08,160 --> 01:25:11,280
Maybe use timer dot
tween to tween the camera

1606
01:25:11,280 --> 01:25:15,690
or just to have it track the
alien if you want larger worlds.

1607
01:25:15,690 --> 01:25:19,320
But we don't end up using
it in the distro as much.

1608
01:25:19,320 --> 01:25:20,890
Our update function is simple.

1609
01:25:20,890 --> 01:25:23,070
We update the launch
marker, update the world,

1610
01:25:23,070 --> 01:25:26,280
and then we process all the bodies
that we flagged as being destroyed,

1611
01:25:26,280 --> 01:25:27,680
which we've already seen.

1612
01:25:27,680 --> 01:25:29,640
We reset destroyed
bodies to an empty table

1613
01:25:29,640 --> 01:25:31,740
because we've processed all of them.

1614
01:25:31,740 --> 01:25:38,504
We actually remove from our
level the obstacle objects

1615
01:25:38,504 --> 01:25:40,670
so that they're no longer
rendered, and we no longer

1616
01:25:40,670 --> 01:25:44,650
try to reference the
bodies that are destroyed.

1617
01:25:44,650 --> 01:25:49,160
And then notice here too,
when we destroy the obstacle,

1618
01:25:49,160 --> 01:25:52,050
we're playing a sound effect
inside this bit of code.

1619
01:25:52,050 --> 01:25:54,650
So we can just do g sounds.

1620
01:25:54,650 --> 01:25:57,260
I put five wooden sound effects
in there just for variability.

1621
01:25:57,260 --> 01:25:58,280
It'll pick a random one.

1622
01:25:58,280 --> 01:26:00,650
And then using to string
at the number, just

1623
01:26:00,650 --> 01:26:03,020
create break one, two,
three, four, five here.

1624
01:26:03,020 --> 01:26:06,420
And then stop and play it.

1625
01:26:06,420 --> 01:26:07,197
Same thing here.

1626
01:26:07,197 --> 01:26:09,530
I have a sound called kill
for when we destroy an alien.

1627
01:26:09,530 --> 01:26:14,240
So when we flag an alien as destroyed
and we remove it from the scene,

1628
01:26:14,240 --> 01:26:16,910
we should also call that sound effect.

1629
01:26:16,910 --> 01:26:27,050
And then if the alien stops
moving in our scene, the player,

1630
01:26:27,050 --> 01:26:31,430
we can get a reference to it here,
self dot launch marker dot alien,

1631
01:26:31,430 --> 01:26:33,667
as opposed to any aliens in our scene.

1632
01:26:33,667 --> 01:26:36,125
When it stops moving, so we
get the average of its velocity

1633
01:26:36,125 --> 01:26:38,510
and if it's less than
1.5, so not perfectly

1634
01:26:38,510 --> 01:26:43,610
still, because it's tedious to
wait that long, but almost still,

1635
01:26:43,610 --> 01:26:48,950
we destroy the alien and then
we create a new launch marker.

1636
01:26:48,950 --> 01:26:52,439
We destroy the alien so that the
world doesn't keep a reference to it

1637
01:26:52,439 --> 01:26:54,230
and then we just create
a brand new marker,

1638
01:26:54,230 --> 01:27:00,530
which has the effect of instantiating
a new alien there when we relaunch.

1639
01:27:00,530 --> 01:27:04,369
And then here, if there are
no more aliens in our scene,

1640
01:27:04,369 --> 01:27:07,410
if we've destroyed all of the aliens,
in this case there's only ever one,

1641
01:27:07,410 --> 01:27:09,800
but there could easily,
with a little more work,

1642
01:27:09,800 --> 01:27:13,040
be a few more aliens in the
scene, if it's set to zero,

1643
01:27:13,040 --> 01:27:14,630
then go back to the start.

1644
01:27:14,630 --> 01:27:18,160
Which we saw before when we
finally killed the alien.

1645
01:27:18,160 --> 01:27:19,910
And then all we're
doing here is deferring

1646
01:27:19,910 --> 01:27:26,090
rendering to the individual objects
we want to render, the launch marker,

1647
01:27:26,090 --> 01:27:27,650
the alien, the obstacle.

1648
01:27:27,650 --> 01:27:29,420
We render ground tiles.

1649
01:27:29,420 --> 01:27:34,070
So recall, from our ground example
before we were just using a line,

1650
01:27:34,070 --> 01:27:36,200
an edge shape to represent the ground.

1651
01:27:36,200 --> 01:27:44,630
But if we look at our game, it's a
little hard to see because I'm in 720,

1652
01:27:44,630 --> 01:27:49,250
but there's actually a ground tile here
at the very bottom, a bunch of them.

1653
01:27:49,250 --> 01:27:52,760
And even though we have
all of those tiles,

1654
01:27:52,760 --> 01:27:56,090
all we're doing to detect
collision is just an edge shape.

1655
01:27:56,090 --> 01:28:02,720
So what we're doing is just beyond
having the edge shape in our scene,

1656
01:28:02,720 --> 01:28:09,530
we draw that tile, which is
frame 12 in our sprite sheet

1657
01:28:09,530 --> 01:28:11,930
from negative virtual
width to virtual times 2.

1658
01:28:11,930 --> 01:28:13,850
So three screen widths total.

1659
01:28:13,850 --> 01:28:16,130
And then we just do it in
increments of 35 pixels

1660
01:28:16,130 --> 01:28:17,630
because that's how wide the tile is.

1661
01:28:17,630 --> 01:28:19,856
And that'll just create
a bunch of the same tile

1662
01:28:19,856 --> 01:28:21,230
at the very bottom of our screen.

1663
01:28:21,230 --> 01:28:24,660


1664
01:28:24,660 --> 01:28:28,130
So just a graphical thing, not
really necessarily functional.

1665
01:28:28,130 --> 01:28:31,190
We have the edge shape already in our
scene, but just to make the ground

1666
01:28:31,190 --> 01:28:35,540
look a little larger
than one pixel tall.

1667
01:28:35,540 --> 01:28:38,300
And then if we haven't
launched anything,

1668
01:28:38,300 --> 01:28:40,610
we should display some
instructions here.

1669
01:28:40,610 --> 01:28:45,050
And then if we're at
no aliens left, then we

1670
01:28:45,050 --> 01:28:47,570
should display the victory screen.

1671
01:28:47,570 --> 01:28:51,650
And the victory thing will last
for just a little bit of time,

1672
01:28:51,650 --> 01:28:55,370
because even though self dot
aliens is zero, this bit of code

1673
01:28:55,370 --> 01:28:59,840
doesn't register until after
the velocity of our moving alien

1674
01:28:59,840 --> 01:29:01,520
slows down sufficiently.

1675
01:29:01,520 --> 01:29:05,420
So this will get called when we're
just about to finally stop moving,

1676
01:29:05,420 --> 01:29:09,500
and then we check to see, oh, OK,
do we indeed have no aliens left?

1677
01:29:09,500 --> 01:29:12,380
If not, time to go back to the start.

1678
01:29:12,380 --> 01:29:13,475
We've completed a level.

1679
01:29:13,475 --> 01:29:15,350
And then you obviously
would just change this

1680
01:29:15,350 --> 01:29:19,179
to go to be next level if you
ended up implementing more

1681
01:29:19,179 --> 01:29:20,720
levels in your game besides just one.

1682
01:29:20,720 --> 01:29:23,600


1683
01:29:23,600 --> 01:29:27,550
Beyond that, that's pretty much all
of the code that's in this example.

1684
01:29:27,550 --> 01:29:32,300
It's fairly, I would say,
unsophisticated relative

1685
01:29:32,300 --> 01:29:33,260
to prior examples.

1686
01:29:33,260 --> 01:29:35,630
But mainly, the burden
is learning how to use

1687
01:29:35,630 --> 01:29:38,960
the physics engine, the
Box2D physics engine, which

1688
01:29:38,960 --> 01:29:42,240
itself is quite a few functions.

1689
01:29:42,240 --> 01:29:47,060
It's some of the longest documentation
on Love2D's wiki, I think.

1690
01:29:47,060 --> 01:29:50,270
But the principles are
pretty simple, in my opinion.

1691
01:29:50,270 --> 01:29:54,905
I think it's actually quite easy to get
rolling with a lot of cool features.

1692
01:29:54,905 --> 01:29:57,617


1693
01:29:57,617 --> 01:30:00,200
The vast majority of which I
don't think we even really cover,

1694
01:30:00,200 --> 01:30:03,920
at least in terms of what you can
do with compound objects and joints

1695
01:30:03,920 --> 01:30:06,260
and things like that,
which really start to go

1696
01:30:06,260 --> 01:30:12,260
into the world of more sophisticated
and interesting physical simulations.

1697
01:30:12,260 --> 01:30:16,130
Things like I alluded to before, pulleys
and tanks and other things like that.

1698
01:30:16,130 --> 01:30:19,580
Some features that we could look
at potentially expanding upon

1699
01:30:19,580 --> 01:30:21,920
if we wanted to make our
game more interesting,

1700
01:30:21,920 --> 01:30:24,430
is more shapes for our objects.

1701
01:30:24,430 --> 01:30:28,280
So if we look at our
sprite sheet here, we

1702
01:30:28,280 --> 01:30:33,290
can see there are things like roofs
and circles and things like that.

1703
01:30:33,290 --> 01:30:36,710
So more interesting obstacles
beyond just square rectangular

1704
01:30:36,710 --> 01:30:37,590
shaped obstacles.

1705
01:30:37,590 --> 01:30:40,790


1706
01:30:40,790 --> 01:30:44,540
Go back to-- like I said
before, compound obstacles.

1707
01:30:44,540 --> 01:30:47,240
So a bunch of things
put together via joints.

1708
01:30:47,240 --> 01:30:51,210
So pulleys, there's motors, weld
joints, which you can use to-- you

1709
01:30:51,210 --> 01:30:56,840
can affix a roof to a square and then
have two pieces that are tied together.

1710
01:30:56,840 --> 01:30:59,330
And you can make arbitrarily
complex and shaped things

1711
01:30:59,330 --> 01:31:01,010
and just be really interesting.

1712
01:31:01,010 --> 01:31:03,890
And that big thing, that
body with all these fixtures,

1713
01:31:03,890 --> 01:31:09,740
will collide just as any other
thing would, thanks to Box2D.

1714
01:31:09,740 --> 01:31:13,670
As I alluded to before, instead
of having levels to be hard coded

1715
01:31:13,670 --> 01:31:19,100
into our level class, maybe define them
in a Lua file called levels dot Lua.

1716
01:31:19,100 --> 01:31:22,070
And then just have aliens
be a table, obstacles

1717
01:31:22,070 --> 01:31:23,870
be a table, and then
whatever else, however

1718
01:31:23,870 --> 01:31:25,869
more complicated you want
to get with your game.

1719
01:31:25,869 --> 01:31:27,260
You can add more things.

1720
01:31:27,260 --> 01:31:32,409
But just have it be represented
as simple data structures.

1721
01:31:32,409 --> 01:31:34,700
So aliens that maybe have
different shooting mechanics.

1722
01:31:34,700 --> 01:31:37,280
So if you've played Angry Birds
you're familiar with the fact

1723
01:31:37,280 --> 01:31:40,070
that some birds will split
off into multiple birds.

1724
01:31:40,070 --> 01:31:44,150
Some birds will dive and go super fast
and break through all the obstacles

1725
01:31:44,150 --> 01:31:45,290
in their path.

1726
01:31:45,290 --> 01:31:48,020
Some birds will explode,
and then their explosion

1727
01:31:48,020 --> 01:31:50,610
affects all of the
obstacles around them.

1728
01:31:50,610 --> 01:31:52,970
So there's a lot of
different game play mechanics

1729
01:31:52,970 --> 01:31:57,240
you can implement using different
types of birds or aliens.

1730
01:31:57,240 --> 01:32:01,670
And then different obstacle materials
is another direction we could go.

1731
01:32:01,670 --> 01:32:04,280
And it's supported out of
the box with the sprite sheet

1732
01:32:04,280 --> 01:32:08,300
that I provided because
it has sheets for metal

1733
01:32:08,300 --> 01:32:10,080
and glass and explosive material.

1734
01:32:10,080 --> 01:32:12,080
So there's a lot of
different interesting things

1735
01:32:12,080 --> 01:32:15,800
you could do just by changing up what
materials you're using in the game.

1736
01:32:15,800 --> 01:32:19,250
And obviously those will have different
densities and behave in different ways.

1737
01:32:19,250 --> 01:32:21,450
So assignment five is a
fairly simple assignment.

1738
01:32:21,450 --> 01:32:24,320
So this is just as I alluded to before.

1739
01:32:24,320 --> 01:32:27,620
The task here is to
split the bird that you

1740
01:32:27,620 --> 01:32:31,850
shoot by pressing Spacebar when
it's in the bird-- the alien, when

1741
01:32:31,850 --> 01:32:35,360
it's in the air, press Spacebar
and have it split into three.

1742
01:32:35,360 --> 01:32:37,680
So you have your one that
you're shooting already.

1743
01:32:37,680 --> 01:32:39,470
So it should just shoot off two more.

1744
01:32:39,470 --> 01:32:41,600
One that's angled higher,
one that's angled lower.

1745
01:32:41,600 --> 01:32:45,945
And all of those should be
interactable with your game world.

1746
01:32:45,945 --> 01:32:46,820
And that's really it.

1747
01:32:46,820 --> 01:32:48,944
So if you can do that then
it'll show that you know

1748
01:32:48,944 --> 01:32:52,580
how to effect the Box2D game world.

1749
01:32:52,580 --> 01:32:55,574
Next time, next lecture,
we'll be talking about--

1750
01:32:55,574 --> 01:32:57,365
the theme is going to
be Pokemon, but we'll

1751
01:32:57,365 --> 01:33:03,057
be talking about more generally RPGs
and turn-based games of that nature.

1752
01:33:03,057 --> 01:33:05,390
It won't maybe necessarily
look quite as pretty as this.

1753
01:33:05,390 --> 01:33:08,390
But we'll be striving
for a similar over world

1754
01:33:08,390 --> 01:33:11,937
that we can walk around and then engage
in fairly simple turn-based battles

1755
01:33:11,937 --> 01:33:12,770
and stuff like that.

1756
01:33:12,770 --> 01:33:15,530
And also, we'll be talking
about user interfaces and things

1757
01:33:15,530 --> 01:33:18,080
like dialogue and stuff like that.

1758
01:33:18,080 --> 01:33:20,332
But that was it for
lecture six, Angry Birds.

1759
01:33:20,332 --> 01:33:21,290
I'll see you next time.

1760
01:33:21,290 --> 01:33:23,140
Thank you.

1761
01:33:23,140 --> 01:33:24,251