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‫Hello and welcome back.

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‫In this video, we're going to talk about how we can speed up our tank.

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‫We'd like to control exactly how fast our tank is moving.

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‫And right now we're just passing in this delta location vector into add act, a local offset, and we

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‫have no control over how fast the tank is moving.

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‫It's actually moving quite slow.

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‫So we're going to make a speed variable that we can use to control that speed.

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‫And we're also going to take into account the frame rate of our game as our game is changing frame rate

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‫from frame to frame.

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‫We actually are not getting consistent movement.

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‫So to take that frame rate into account, we're going to talk about something called Delta Time.

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‫So we're here in the editor and if I hit play and I start moving the tank around, it's not something

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‫you can really notice necessarily.

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‫But our tank is not moving in a consistent rate from frame to frame.

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‫And the reason is because our frame rate changes and up here at the top left of the viewport is a little

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‫dropdown.

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‫If I click that, there's a checkbox next to show DPS PES means frames per second.

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‫If I check this, then at the top right I see my frames per second.

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‫And just below that, how many milliseconds have passed since the last frame?

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‫And these values change from frame to frame.

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‫If I hit play, you might have missed it, but the frame rate went down and then came back up because

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‫during that beginning stage of the game, lots of things were happening.

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‫All of the actors were calling their begin play functions and there's some behind the scenes setup for

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‫the world.

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‫Now, if I start playing the game, that 120 apps that I'm getting is changing from frame to frame,

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‫even though it hovers around 120.

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‫So the reason this causes inconsistent movement is because as the frame rate goes down, those tick

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‫updates are being called less often.

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‫And if we're moving this tank by the same amount each frame, then we're relying on that frame rate

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‫to stay consistent, to get that consistent movement.

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‫And when the game gets more complicated, the frame rate variations are going to get worse and worse.

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‫So we need to make sure that we're adjusting for that by using something called Delta Time.

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‫So what's this mysterious Delta time?

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‫Well, let's say we have this timeline here starting at 0 seconds and increasing as time moves on.

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‫Now, as time moves on were ticking, this means that the tick function is being called.

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‫But notice that the tick function is not very consistent.

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‫Sometimes it's called very rapidly and sometimes it's called less often.

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‫This is because your computer must make calculations on a frame by frame basis, and sometimes those

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‫calculations take up more resources from your computer, and that can slow down our frame rate.

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‫Now, this delta time variable that we have in the tick function is the amount of time that's passed

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‫since the last frame.

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‫So here it may be 0.1 seconds.

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‫It really depends on the CPU usage and how that varies.

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‫So as your CPU usage varies, your delta time is also going to vary.

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‫And this means that when we have more frames per second, we have more function calls.

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‫Now if we're calling add actor local offset more often, then we're going to see our pond moving faster

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‫and it won't have a consistent movement rate.

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‫So the solution is to scale the movement by Delta time.

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‫So if Delta time is 0.1 and we want to move our pond by, say, ten centimeters per second, scaling

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‫that movement by 0.1 seconds gives us the exact amount of movement we need for a frame update time of

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‫0.1 seconds.

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‫Now consider this part over here where we have a smaller delta time, meaning TIC is being called more

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‫often.

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‫Let's say that delta time here is 0.0 1 seconds.

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‫So TIC is being called ten times more often over here.

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‫Well, we could simply scale our movement by 0.01 for this particular frame, and that way we'll move

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‫our pond by ten centimeters per second times, 0.0 1 seconds.

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‫So therefore we're moving the pond a tiny amount since TIC is being called much more frequently.

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‫Doing this ensures that our pond will move in a consistent manner independent of the changes in frame

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‫rate.

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‫So back here in VSE code, let's think about how we like to take care of this issue.

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‫We have our delta location vector and we're setting its x equal to value, but we know we'd like to

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‫scale value by Delta time.

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‫So I'm just going to put a little comment here and say X equals value times, delta time, meaning we'd

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‫like to scale value by Delta time.

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‫Now once we do this, we're going to make value very small because Delta time itself is a very small

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‫value, especially if your frame rate is very high.

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‫So we're also going to need to scale this by something.

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‫Else a sort of speed variable, and we can decide what this value should be in order to control the

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‫tanks speed.

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‫So we have a little bit of pseudocode here to guide us and we now just need to implement this by creating

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‫a value for speed and finding out how we can get this delta time value.

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‫So let's talk about how we can access Delta time from the move function.

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‫Now, Unreal Engine has multiple ways to get a hold of Delta time.

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‫In fact, if you look at the tick function that we have in base upon Delta, time is a float input parameter.

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‫So if we're working in the tick function, we already have access to Delta time, but in tank DHCP,

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‫our move function does not have that input parameter, but unreal engine has its ways.

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‫One way is to access a function called get world delta seconds, which exists in a class called U gameplay

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‫statics.

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‫As the name suggests you game play statics has lots of static functions that assist in programming gameplay.

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‫Get World Delta seconds returns delta time.

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‫Now it has an input parameter.

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‫Here it takes a world context object.

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‫You'll see this a lot in Unreal Engine.

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‫A lot of static functions will require a world context object.

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‫The world is an object of type you world.

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‫It's the top level object of our game.

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‫It represents our map which contains all of the associated objects in our game.

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‫Now static functions such as get world delta seconds have no idea which world we're in.

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‫We need to tell this function which world we're in so it can access that world and get that delta time

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‫value.

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‫Now, in order to tell it which world we're in, we can pass in a pointer to an object that exists in

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‫that world.

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‫While we're working in the tank class, we can pass in the key word this.

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‫This is a key word that we can use inside of any class in C++.

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‫What the this key word is, is a pointer to the instance of any particular object that we're working

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‫in.

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‫So if we're working in the tank class, this is a pointer to the tank that we're in.

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‫So functions that require a world context object can often receive this as the input parameter because

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‫the tank we're working in exists in the correct world.

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‫So get world delta seconds will know which world it's in and can retrieve us the appropriate delta.

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‫Time for that world.

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‫So if we're calling get world delta seconds from within the -- class, we're going to pass this in

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‫as the world context object.

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‫So you now have all the tools you need to control the tanks speed.

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‫So what you're going to do is create a speed variable, make this a float, and put it in a private

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‫section in the tank class.

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‫Now expose this to blueprints so we can adjust it as we're developing, which means you're going to

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‫give it a you property and use the appropriate you property specifiers that correspond to the level

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‫of exposure you would like.

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‫Now in the MOV function, we have that bit of pseudo code that we placed in as a comment.

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‫So use that as a guide.

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‫You're going to take the delta location, F vector and scale.

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‫It's X by delta time.

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‫We just saw how we can access delta time using U gameplay statics.

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‫And you're also going to scale X by the speed variable.

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‫Now, because we're using a function in gameplay statics, you're going to need to include the header

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‫file for gameplay statics.

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‫Now I've shown you multiple times how I find the include for a particular class using the unreal engine

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‫documentation.

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‫So I'm going to challenge you to search for your gameplay statics in the Unreal Engine documentation

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‫and find that header file.

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‫And if you can't find it, then just find the link in the resources for this video, which will give

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‫you the documentation for your gameplay statics but try to find it on your own.

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‫First pause the video and control the tank speed now.

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‫Okay.

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‫So I have my pseudo code to guide me and I need to scale value by delta time and by speed.

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‫So first I'm going to create my speed variable.

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‫Now back in tank h.

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‫Here's where I can place the speed variable.

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‫However, if you'll recall from a practice exercise in an earlier lecture I added a float called Speed

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‫to the Base Pond class.

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‫Now I don't need the speed variable here in base pond.

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‫This was just practice, so I don't really need it here.

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‫In fact, I don't need these other 30 twos that I created to demonstrate that you property specifiers.

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‫So I'm just going to highlight all of these and delete them from the base pond class.

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‫I don't want them anymore.

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‫So they're gone.

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‫Now, you might also remember that I referenced that speed variable in the pond tank blueprint.

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‫So I'm going to open up BP pond tank.

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‫And here in the event graph, there's that speed variable that I referenced.

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‫Since I no longer need this anymore, I'm going to go ahead and delete those nodes and compile and save

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‫my BP pond tank.

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‫Okay.

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‫After cleaning up all that, I'm going back into tank to add my speed variable.

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‫And this is going to be in the private section here.

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‫I'm going to add it just above the move function and it's going to be a float called speed.

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‫Now I'm going to give it an initial value here.

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‫I think I'll try 200 F and see how that works.

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‫But since I'd like to be able to edit this in the editor as I'm developing, it's going to get a new

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‫property macro and I'd like to be able to edit this on instances and on the default.

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‫So I'm going to make it edit anywhere.

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‫Now, you didn't have to do this, but I'm giving it a category.

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‫I'll create a new category called movement.

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‫Now exposing it to the event graph is optional.

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‫I'm going to hold off on that because I don't think I'll need to access it in the event graph.

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‫If I need to.

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‫In the future, I can expose it with blueprint, read, write or blueprint read only and use that meta

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‫allow private access specify.

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‫But for now I'm not going to.

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‫So I have a speed variable and here in tank DHCP, I'm going to take value and scale it by speed.

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‫Now the last thing to do is scale value by delta time which means I need you gameplay statics.

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‫So here's Unreal Engine's documentation.

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‫I'm going to go ahead and search for you gameplay statics and here it is you game gameplay statics.

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‫So I just need to scroll down to the include line and copy this and back in tank CP.

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‫I can paste it in.

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‫Now that I have access to new gameplay statics, I can get Delta time so I'm going to multiply by you.

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‫Gameplay statics get world delta seconds and as we saw, this needs a world context object.

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‫You can even see with the pop up it's asking for a world context object.

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‫So I'm going to pass in this.

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‫So now that I'm setting Delta locations X to value times, speed, times, delta time, I'm going to

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‫compile this.

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‫So we have a successful compile.

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‫So back here in the editor, I can go into BP Pond Tank and there's my speed right there.

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‫And if I select the instance of the tank in the world, I can search in the details panel for movement

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‫and there's the speed and I can set it to any value I like.

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‫If I crank this up and hit play, then I'm moving quite a bit faster.

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‫So this is the advantage of exposing the variable to blueprints.

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‫I can experiment and find a good speed that works for me.

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‫All right, so that's looking great.

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‫I'm going to go ahead and stop showing the FPSO now.

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‫And now we have our speed variable and we can change it.

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‫And that change will be reflected in the movement of my pawn.

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‫So we're now controlling the movement speed of our tank and we have a nice speed variable that we expose

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‫to blueprints and we can set that as we're developing an experiment with its value.

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‫We also learned about Delta time and why it's important to scale our movement by Delta time.

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‫So it's frame rate independent as the frame rate changes will still get smooth, consistent movement

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‫with our tank.

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‫So looking back at our section plan, we're almost done with our first bullet point.

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‫We've created a tank and it can move throughout the world.

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‫Our second point is to handle input with WASD keyboard movement and mouse input as well.

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‫We've got that W and SW part down, but we still need to be able to use the A and D keys and we're going

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‫to use those to rotate the tank.

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‫So we're making good progress in the videos to come.

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‫We'll work on finishing our ability to move the tank.

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‫I'll see you soon.