Unreal Development Kit Game Programming with UnrealScript：Beginner's Guide

上QQ阅读APP看书，第一时间看更新

Time for action – Using structs

Going back to our basket of kittens example, what if there were other things in the basket besides kittens? How would we represent them?

Let's create a struct at the top of our AwesomeActor class and put a few things in it.
```
struct Basket
{
    var string BasketColor;
    var int NumberOfKittens, BallsOfString;
    var float BasketSize;
};
```
Now we have two types of items in the basket as well as some variables to describe the basket itself.
Now we need a variable of that struct so we can use it:
```
var Basket MyBasket;
```

Now we can change the values in our PostBeginPlay function.

function PostBeginPlay()
{
    MyBasket.NumberOfKittens = 4;
    MyBasket.BasketColor = "Yellow";
    MyBasket.BasketSize = 12.0;
    MyBasket.BallsOfString = 2;}

That seems easy enough to handle. Let's try something a bit more complex.

I heard you like structs, so we'll Inception-ize it by adding a struct inside a struct.
```
struct SmallBox
{
    var int Chocolates;
    var int Cookies;
};
```

Now let's put a box inside our basket struct.

struct Basket
{
    var SmallBox TheBox;
    var string BasketColor;
    var int NumberOfKittens, BallsOfString;
    var float BasketSize;
};

Now our class should look like this:

class AwesomeActor extends Actor
    placeable;

struct SmallBox
{
    var int Chocolates;
    var int Cookies;
};

struct Basket
{
    var SmallBox TheBox;
    var string BasketColor;
    var int NumberOfKittens, BallsOfString;
    var float BasketSize;
};

var Basket MyBasket;

function PostBeginPlay()
{
    MyBasket.NumberOfKittens = 4;
    MyBasket.BasketColor = "Yellow";
    MyBasket.BasketSize = 12.0;
    MyBasket.BallsOfString = 2;
}

defaultproperties
{
    Begin Object Class=SpriteComponent Name=Sprite
        Sprite=Texture2D'EditorResources.S_NavP'
        HiddenGame=True
    End Object
    Components.Add(Sprite)
}

Now we're getting somewhere. How would we access the struct inside a struct? Using the same method as before, we would access the box like this:
```
MyBasket.TheBox
```
So accessing variables inside the box struct would look like this:
```
MyBasket.TheBox.Chocolates = 2;
```
Easy enough. It would work the same way with arrays. Let's say we added a static array of fortune cookie messages to our basket. Our new struct would look something like this:
```
struct Basket
{
    var string Fortunes[4];
    var SmallBox TheBox;
    var string BasketColor;
    var int NumberOfKittens, BallsOfString;
    var float BasketSize;
};
```
To assign a value to one of them, we would use the same method as before:
```
MyBasket.Fortunes[2] = "Now you're programming!";
```

What just happened?

Structs are a powerful tool in UnrealScript, and they're used extensively in the source code. A lot of the code you'll make will involve structs. As an example, think about the one thing that every actor in the game has: A location. How is an actor's location stored? A variable appropriately called Location, which is declared as a 3D position using a Vector variable. If we look in Actor.uc, we can see how a Vector is defined:

struct immutable Vector
{
   var() float X, Y, Z;
};

This leads nicely into our next topic...

Vectors

Simply put, a vector is a 3D coordinate. It may be used to represent an actor's location, velocity, or even the angle of a surface. They're used a lot in UnrealScript, so even though they're just a struct, there are a lot of things we can do with them on their own. Let's take a look.