Corona SDK: Create a Teeter-like Game - Interface Creation

In this tutorial series, you’ll learn how to create a Teeter Inspired game. The objective of the game is to balance a ball and avoid the obstacles to get to the goal. Read on!

Step 1: Application Overview

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

The player will be able to use the accelerometer of the device to move a ball across the stage, 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 prefered 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()
physics.setGravity(0, 0)

Step 11: Game 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 View

The game view is composed by the player, obstacles, and the goal. Add the following lines to your code to handle these elements.

-- [Game View]

-- [Player]

local player

-- [Bars Table]

local bars = {}

-- [Holes Table]

local holes = {}

-- [Goal]

local goal

Step 15: Sounds

These lines store a reference for the sound files.

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

Step 16: Code Review

Here is the full code written in this tutorial alongside with comments to help you identify each part:

-- Teeter like Game
-- Developed by Carlos Yanez

-- Hide Status Bar

display.setStatusBar(display.HiddenStatusBar)

-- Physics

local physics = require('physics')
physics.start()
physics.setGravity(0, 0)

-- Graphics

-- [Background]

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

-- [Title View]

local titleBg
local playBtn
local creditsBtn
local titleView

-- [Credits]

local creditsView

-- [Player]

local player

-- [Bars Table]

local bars = {}

-- [Holes Table]

local holes = {}

-- [Goal]

local goal

-- Sounds

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

Step 17: Declare Functions

Declare all functions as local at the start.

local Main = {}
local startButtonListeners = {}
local showCredits = {}
local hideCredits = {}
local showGameView = {}
local gameListeners = {}
local movePlayer = {}
local onCollision = {}
local alert = {}
local dragPaddle = {}

Step 18: Game Constructor

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

function Main()
	-- code...
end

Step 19: 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('titleBg.png')
	playBtn = display.newImage('playBtn.png', display.contentCenterX - 35.5, display.contentCenterY + 10)
	creditsBtn = display.newImage('creditsBtn.png', display.contentCenterX - 50.5, display.contentCenterY + 65)
	titleView = display.newGroup(titleBg, playBtn, creditsBtn)
	
	startButtonListeners('add')
end

Step 20: Start Button Listeners

This function adds the necesary listeners to the TitleView buttons.

function startButtonListeners(action)
	if(action == 'add') then
		playBtn:addEventListener('tap', showGameView)
		creditsBtn:addEventListener('tap', showCredits)
	else
		playBtn:removeEventListener('tap', showGameView)
		creditsBtn:removeEventListener('tap', showCredits)
	end
end

Step 21: Show Credits

The credits screen is shown when the user taps the about button, a tap listener is added to the credits view to remove it.

function showCredits:tap(e)
	playBtn.isVisible = false
	creditsBtn.isVisible = false
	creditsView = display.newImage('credits.png', 0, display.contentHeight+40)
	transition.to(creditsView, {time = 300, y = display.contentHeight-20, onComplete = function() creditsView:addEventListener('tap', hideCredits) end})
end

Step 22: Hide Credits

When the credits screen is tapped, it'll be tweened out of the stage and removed.

function hideCredits:tap(e)
	playBtn.isVisible = true
	creditsBtn.isVisible = true
	transition.to(creditsView, {time = 300, y = display.contentHeight+creditsView.height, onComplete = function() creditsView:removeEventListener('tap', hideCredits) display.remove(creditsView) creditsView = nil end})
end

Step 23: Show Game View

When the Play button is tapped, the title view is tweened and removed revealing the game view.

function showGameView:tap(e)
	transition.to(titleView, {time = 300, x = -titleView.height, onComplete = function() startButtonListeners('rmv') display.remove(titleView) titleView = nil end})

Step 24: Goal

Here we place the goal in its position. We also give it a name to identify it when a collision occurs.

	-- Goal
	
	goal = display.newImage('goal.png')
	goal.x = 439
	goal.y = 31
	goal.name = 'g'

Step 25: Walls

Walls are created around the stage to prevent the ball from going away.

-- Walls
	
	local left = display.newLine(-1, 0, -1, display.contentHeight)
	local right = display.newLine(display.contentWidth+1, 0, display.contentWidth+1, display.contentHeight)
	local top = display.newLine(0, -3, display.contentWidth, -3)
	local bottom = display.newLine(0, display.contentHeight, display.contentWidth, display.contentHeight)

Step 26: Bars

These bars are obstacles in the stage. Add them with the next lines:

	-- Bars
	
	local b1 = display.newImage('bar.png', 92, 67)
	local b2 = display.newImage('bar.png', 192, -2)
	local b3 = display.newImage('bar.png', 287, 67)
	local b4 = display.newImage('bar.png', 387, -2)

Step 27: Holes

You can say that the holes are the "enemies" of this game, if the ball touches one, the game will end.

	-- Holes
	
	local h1 = display.newImage('hole.png', 62, 76)
	local h2 = display.newImage('hole.png', 124, 284)
	local h3 = display.newImage('hole.png', 223, 224)
	local h4 = display.newImage('hole.png', 356, 114)
	local h5 = display.newImage('hole.png', 380, 256)
    -- Name holes for collision detection
    h1.name = 'h'
	h2.name = 'h'
	h3.name = 'h'
	h4.name = 'h'
	h5.name = 'h'

Step 28: Player

Next we add the ball. This will be moved by the player using the accelerometer.

	-- Player
	
	player = display.newImage('player.png')
	player.x = 49
	player.y = 288
	player:setReferencePoint(display.CenterReferencePoint)

Next Time...

In this part of the series you've learned the interface and the basic setup of the game. Stay tuned for part two, where we will handle the logic of the application, buttons, behavior, and more. See you next time!

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