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We'll come back again in this lesson and we're going to talk about you I'd dynamics and dynamics is

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one of the few different physics engines that the iOS SDK offers us and we use dynamics for usually

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the lower end to kind of interactions.

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If you want to do something with heavy physics engine you know interactions then you can rely on a sprite

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kit or the scene kit.

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But if you have to do some basic animations that are depending on the physics engine then you can use

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the dynamics within your views.

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So before you go to school and actually show you how we're going to program this let me show you the

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project that I'm going to work on.

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So we get a sense of what's happening.

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So in this project every time I click this little box falls and as it falls it makes a lot of collisions

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either with this barrier or with the view boundaries and it counts how many times it has collided with

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different objects.

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So once again it falls and it makes a lot of collisions and then it lands number three.

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Again so on and so forth.

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So that's essentially the goal of the project and the use of dynamics.

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Now let's see how we're going to do that.

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I'm going to go ahead into ex-cult and start a new application called it you might say nomics a story

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about the things that I need or does I need a little label a new label.

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I'm going to place it up there maybe a little bit larger such as two five six that's too large maybe

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1 2 8 1 2 8.

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And it is going to show me the number of the collisions which is by default 0.

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Maybe if I go on color which is like purple and then I'm going to have another you I view.

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So that's going to be you.

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I view that I place it here.

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That's like the barrier that my box essentially bumps against So I'm going to make that one.

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Maybe dark gray color.

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I know I'm going to have to add them into my programming interface so I'm going to come in here say.

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So this one I'm going to call it my box which is a level of force.

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This other one I'm going I call the barrier barrier.

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Now we're almost done in here.

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There's one more thing I have to do or this is something we probably haven't done before.

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So let me show you how we do it.

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And that is sitting an ID for an object and we need to see the ID because you want to be able to find

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that object by its eye and draw a rectangle around it.

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And that's something that we'll see real soon.

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Don't worry about that part.

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But setting an idea is here in the storyboards so I'm going to go up here in the class and I'm going

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to say there is a label for this object and that is going to be called let's say that your oil or anything

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that you want as long as it is a distinct unique value.

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So unless it is to bury your ID for now.

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So that's all I have to do in this story what we're calling site at in here.

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Let's go ahead and add a few things that may form out all of this so it is cleaner.

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The first thing I want to add is a white dynamic animator as well as a light gravity behavior so I'm

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going to say that I'm going to call this one main engine that's like the engine of the entire physics

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essentially that's going to be a dynamic animator and I knew that gravity is going to survive and I'm

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going to call it dynamic gravity or draw or gravity.

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Right.

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The whole thing that's going to be a come at you like gravity behavior.

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So this one essentially calculates everything in the scene.

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This one adds a gravity to the objects that we wanted to have them to.

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So let's go ahead to the next thing and I'm actually going to go ahead and add these things.

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I should have done it in the view of the law but I'm going to do it in the touch.

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And that simply because I wanted this to happen every time I touch somebody.

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So I'm going to say let's do it in the touches and.

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And what we have to do is we have to initialize this.

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I'm going to say Main engine becomes you dynamic animator and then is going to say Give me a reference

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if you say reference view itself that if you do it here within this city you essentially then the next

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thing is I'm going to have to initialize my dynamic gravity so I'm going to sync my dynamic gravity

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becomes you gravity behavior and then is going to say which items do you want to add this to.

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I only have one item so I'm going to have to make an array of my only item which is my box.

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So now it's been added there and then I'm going to have to add this behavior to my engine.

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So you might have different kinds of gravities and you might have different kind of physical forces

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and you have to choose which ones you want to add to your engine.

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So I'm going to say Main engine dart at the behavior and this behavior which understands the gravity

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for the box.

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Now this is all live and it will work properly if we only wanted to add a gravity to this object.

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Let's go ahead and try that out and see how this would fare.

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Up until this point.

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So now that the simulator is up if I touch it will see that the box essentially falls to the screen

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and that's simply because the gravity keeps pulling it down later on I would add something that every

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time that touches and we want to begin this dynamic animation we reset the location of the box right

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up here.

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But for now this was quite good.

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It showed me that it's working but it doesn't cause any collisions.

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And that's the most interesting part.

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Let's go ahead and doubt.

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I'm going to go back to school and say I have a variable called Collision and that collision is going

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to be a collision behavior.

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This is the behavior that calculates when objects bounce against each other or bump into each other.

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And the first kind of collision I want to calculate is the collision against this barrier.

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So I'm going to go ahead and say that have your function.

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So.

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Because the court is going to become a long coat so I'm going add them inside the new function say this

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function is actually called Collision with objects and collision with objects does these things you

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first find the boundary of the barrier view that we want to collide against.

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So I'm going to say this guy and that guy becomes ads about the tweets of boundary and an.

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And I'm going to say the boundary that I want to add the identifier for it is that's a name that we

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gave for as very your ID.

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That's the identifier I'm going to say get it as a..

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Copying for and the pads that you're going to make is a path like this for a rectangle made of barrier

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object dot frame.

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So get the ID from that object get that identifier and produce a barrier based on that which is a busy

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spot simply because objects that they want to collide with each other.

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They can be calculated based on their look based on the fact that they are a white label.

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They have to be calculated based on a busy path.

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So I have that one something I did for getting your is we never initialize the collision.

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So that's something I have to do it in here.

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And for that I'm going to say let's have that collision to become a UI collision behavior of the items

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and the item again is only this one guy.

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So my box.

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So that collision is essentially initialized for my box and then the collision itself is being calculated

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based on this particular object.

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For now while this is the bare minimum of what you could do to essentially calculate the collision.

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The other things that are kind of optional and you could add for instance you could add a list to your

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object.

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So I'm going to say Let let's call it my behavior or my Buck's behavior or anything of the sort becomes

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you UI dynamic Eidem behavior UI dynamic Eidem behavior and the item for it is going to be let's say

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in this case my box.

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So I'm going to say my box.

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So these are the behaviors of specific items not the overall engine as we had it in years.

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So the specific behavior they want to have for this object I'm going to say it has an plasticity plasticity

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of let's say point six.

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It's a lower number than the default value.

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And I'm going after say Main engine you have to add this behavior to it as I'm going to say as the behavior

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this one tweet is about.

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I mean renamed.

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So that's my box behavior.

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So that's a better name for it.

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So my box behavior also has some optional values I'm going to write this to you remember this.

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Optional.

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And you can play along with them at some point.

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And now you still have two other things that you have to do.

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One of them is that we have to call this function at some point and the other one is we have française

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Surely this collision behavior to our engine.

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So I'm going to come in here and say once I made the collision Let's go ahead and say Main engine that

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adds that behavior and add that collision to it because it has to be there so it gets calculated within

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the main engine.

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And then of course let's call this function.

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Every time we had the touches and like I said touches on that is not the best place to put this.

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I'm just doing it because I want to simplify my life and I'm teaching this to you guys.

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So let's go ahead and run this up again.

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And if you run it now we should be able to see the box making a collision with the bat.

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And that's exactly what we wanted to see.

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Now the only thing that is left us thing is making sure that the box also collides with the boundaries

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of our view.

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And I'm going to do that in a different function.

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Some that come in here and say I haven't you function Let's call this one religion with view.

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And in my collision with the view I'm going to have to say religion not translate reference bounce into

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boundaries and that is true.

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And that's essentially all I have to doing here.

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So I'm going to say collision that view is also the function you want to call every time that touches

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and and there's still one more step you have to do with I want to show that to you.

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Once we've done the application successfully again in here.

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So what's the uploads up on the simulator if I touch it makes collisions with a variety of different

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objects.

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And now that I touch again doesn't anything doesn't really happen.

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So it doesn't jump back up there.

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So the fix that I'm going to come in here with touches on that say my box Dart Center.

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Make it a CG point of this place said something like 200 and a hundred even though it's not very good

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you know scientific way of doing it.

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You probably want to have exact numbers very you want to place it or you essentially want it to remember

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where the original place was.

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But I think for me just you know it's suffice to do it like that.

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So now it goes.

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Makes that up again.

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It does again and this time we didn't actually fall.

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So that's good.

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It shows me is working except that the numbers are probably very good.

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So maybe a hundred fifty would do better.

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Now the next thing that is the last thing in this project is understanding what happens every time that

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the collision is actually called.

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So to do that I'm going to come in here and say that I have the collision I'm going to have to say this

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sky collision not collision delegate's which is of the type you are in collision behavior delegate's

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becomes self and I have to add the UI collision behavior or delegate here you want collision behavior.

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Delegate's which is not that

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yes that's the one you like collision behavior or delegate becomes an other function that other protocol

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for your controller.

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And now I can have the function that has me even be qualified with something.

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And that's the only thing that we still have to do.

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We have to know every time that I've made some things so we can actually use that information to do

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something.

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And you know I'm with you as one of the collision behaviors and the one I want to use is the one that

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has an Eden and a boundary and it ends.

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So it's going to be this one is between two dynamic items.

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This one is a mother as a mother.

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This one to this one to a dynamic item on the boundary has ended.

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This is the one I want to use so I'm going to say this is my collision behavior.

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So let's get most of the data that is facing this from what it does is this it says every time a collision

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happens.

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If I'm using the delegation here which I am I will find out who has been colliding with what with what

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boundary essentially and that I am the object is the one I'm most interested in.

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So I'm going to sit.

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Let's I'm going to call it my label to become this item as you I that simply because I know that item

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that is in the collision is of the type you are labeling here.

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And what I want to do is I want to count up the number on it so we know how many collisions are happening.

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So to do that I'm going to actually have a count that I'm going to call these collision counter which

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is a default of zero on collision counter adds up every time we do find in your collision.

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So I'm going to say plus equal one and I'm about to say sure it's on my label.

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So my label that text becomes whatever value we find on collision counter.

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So with that we should be able to see a new collaging count happening every time a new collision is

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actually happening.

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Just go ahead and see if that works.

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I'm hoping with

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so now the numbers are counting go up and 16 was the final number.

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Let's try it again.

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And of course they have to reset it now.

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I can't count the number 31 minus 16.

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This time was less.

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So let's go ahead and reset the college and counting the touches begin.

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And that's right.

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Zero.

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And I also that I change the color of the labor depending on the value of the coalition Countach I'm

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going to say if college encounter modulus to zero and even the numbers do something tells you something

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else then say my dog died doing color becomes a white color color dots purple and otherwise it becomes

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a siren color for instance a more a different color.

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So now we should be able to see a collision counter counting up showing the number and the colors essentially

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switching between one to another depending on the number.

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So under all the numbers we see so on on the even numbers we see the purple color.

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Yes.

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So that's about that.

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This is you own.

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A lot of code and it's just the starting part of it is a lot of other things you can do with it.

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And I hope you can use it to do some other them games or basic animations in your applications.

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That's a lot of that.

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And let's move on to our next.