Build an Air Hockey Game - Interface Creation

In this tutorial series, you'll learn how to create an Air Hockey game. The objective of the game is to hit the puck using the paddles to raise the score. Read on!

Also available in this series:

1. Build an Air Hockey Game - Interface Creation
2. Build an Air Hockey Game - Adding Interaction

Step 1: Application Overview

Using pre-made graphics, we will code an entertaining game using Lua and the Corona SDK APIs.

The player will be able to hit a puck by dragging the paddle on the screen. You can modify the parameters in the code to customize the game.

Step 2: Target Device

The first thing we have to do is select the platform we want to run our app within, this way we'll be able to choose the size for the images we will use.

The iOS platform has these characteristics:

• iPad: 1024x768px, 132 ppi
• iPhone/iPod Touch: 320x480px, 163 ppi
• iPhone 4: 960x640px, 326 ppi

Because Android is an open platform, there are many different devices and resolutions. A few of the more common screen characteristics are:

• Google Nexus One: 480x800px, 254 ppi
• Motorola Droid X: 854x480px, 228 ppi
• HTC Evo: 480x800px, 217 ppi

In this tutorial we'll be focusing on the iOS platform with the graphic design, specifically developing for distribution to an iPhone/iPod touch, but the code presented here should apply to Android development with the Corona SDK as well.

Step 3: Interface

A simple and friendly interface will be used, this involves multiple shapes, buttons, bitmaps and more.

The interface graphic resources necessary for this tutorial can be found in the attached download.

Step 4: Export Graphics

Depending on the device you have selected, you may need to export the graphics in the recommended ppi, you can do that in your favorite image editor.

I used the Adjust Size... function in the Preview app on Mac OS X.

Remember to give the images a descriptive name and save them in your project folder.

Step 5: Sound

We'll use Sound Effects to enhance the feeling of the game, you can find the sounds used in this example in Soungle.com using the keywords bell and buzz.

Step 6: App Configuration

An external file will be used to make the application go fullscreen across devices, the config.lua file. This file shows the original screen size and the method used to scale that content in case the app is run in a different screen resolution.

application =
{
    content =
    {
        width = 320,
        height = 480,
        scale = "letterbox"
    },
}

Step 7: Main.lua

Let's write the application!

Open your preferred Lua editor (any Text Editor will work, but you won't have syntax highlighting) and prepare to write your awesome app. Remember to save the file as main.lua in your project folder.

Step 8: Code Structure

We'll structure our code as if it were a Class. If you know ActionScript or Java, you should find the structure familiar.

Necessary Classes

Variables and Constants

Declare Functions

    contructor (Main function)
	
    class methods (other functions)

call Main function

Step 9: Hide Status Bar

display.setStatusBar(display.HiddenStatusBar)

This code hides the status bar. The status bar is the bar on top of the device screen that shows the time, signal, and other indicators.

Step 10: Import Physics

We'll use the Physics library to handle collisions. Use this code to import it:

local physics = require('physics')
physics.start()

Step 11: Background

A simple graphic is used as the background for the application interface, the next line of code stores it.

-- Graphics

-- [Background]

local bg = display.newImage('bg.png')

Step 12: Title View

This is the Title View, it will be the first interactive screen to appear in our game, these variables store its components:

-- [Title View]

local titleBg
local playBtn
local creditsBtn
local titleView

Step 13: Credits View

This view will show the credits and copyright of the game, this variable will be used to store it.

-- [CreditsView]

local creditsView

Step 14: Game Background

This image will be placed on top of our previous background to add a Hockey like feeling.

-- [Game Background]

local gameBg

Step 15: Puck

This is the puck graphic, referenced in the next variable.

-- [Puck]

local puck

Step 16: Paddles

Player and Enemy or CPU paddle. Used to hit the puck.

-- [Paddles]

local player
local enemy

Step 17: Score

Score variables are added to display them later on the screen.

-- Scores

local playerScore
local enemyScore

Step 18: Sound

We'll use Sound Effects to enhance the feeling of the game, you can find the sound used in this example in Soungle.com using the keyword bell.

-- Sounds

local bell = audio.loadSound('bell.caf')

Step 19: Walls

The walls where the ball will be able to bounce. These are created using the Corona Display API and then added to the physics engine.

-- [Walls]

local left
local right
local topLeft
local bottomLeft
local topRight
local bottomRight

Step 20: Variables

These are the variables we'll use, read the comments in the code to know more about them.

-- Variables

local lastY --used to animate the credits screen
local timerSrc --a timer for the enemy/cpu movement

Step 21: Declare Functions

Declare all functions as local at the start.

-- Functions

local Main = {}
local startButtonListeners = {}
local showCredits = {}
local hideCredits = {}
local showGameView = {}
local gameListeners = {}
local moveEnemy = {}
local update = {}

Step 22: Constructor

Next we'll create the function that will initialize all the game logic:

function Main()
	-- code...
end

Step 23: Add Title View

Now we place the TitleView in the stage and call a function that will add the tap listeners to the buttons.

function Main()
	titleBg = display.newImage('title.png', display.contentCenterX - 143.5, 50)
	playBtn = display.newImage('playBtn.png', display.contentCenterX - 39.5, display.contentCenterY)
	creditsBtn = display.newImage('creditsBtn.png', display.contentCenterX - 40.5, display.contentCenterY + 65)
	titleView = display.newGroup(titleBg, playBtn, creditsBtn)
	
	startButtonListeners('add')
end

Next Time...

In this part of the series you've learned the interface and the basic setup of the game. In the next and final part of the series, we'll handle the paddle movement, collision detection, and the final steps to take prior to release like app testing, creating a start screen, adding an icon and, finally, building the app. Stay tuned for the final part!