Adding a background and basic UI

We're going to start by adding a background, and two text fields to display the score and game time to the player. Open up PlayState.hx, and we'll add some variables.

Inside the class, add the following variables:

private var background:FlxSprite;
private var txtScore:FlxText;
private var txtTime:FlxText;

The background is a FlxSprite object. It is used when you want to display an art asset or a shape drawn by HaxeFlixel. The txtScore and txtTime variables are FlxText objects, and as the name implies, they're used to display text.

After this, go inside the create function and add the following underneath super.create():

background = new FlxSprite();
background.loadGraphic(AssetPaths.gameBackground__png);
add(background);

In those lines, we are creating a new FlxSprite instance in the background variable, loading our background image using the AssetPaths class, and then using the add function to add the background to PlayState. The add function is...