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Build an Apple Catcher Game - Interface Creation

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In this tutorial series, you’ll learn how to create an Apple Catcher game. The objective of the game is to grab the apples that fall on the screen by dragging the basket. Read on!


Also available in this series:

  1. Build an Apple Catcher Game - Interface Creation
  2. Build an Apple Catcher Game - Adding Interaction

Step 1: Application Overview

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

The player will be able to catch the apples by dragging the basket 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, that way we'll be able to choose the size for the images we will use.

The iOS platform has these characteristics:

  • iPad 1/2: 1024x768px, 132 ppi
  • iPad 3: 2048x1536, 264 ppi
  • iPhone/iPod Touch: 320x480px, 163 ppi
  • iPhone 4/iPod Touch: 960x640px, 326 ppi
  • iPhone 5/iPod Touch: 1136x640, 326 ppi

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

  • Asus Nexus 7 Tablet: 800x1280px, 216 ppi
  • Motorola Droid X: 854x480px, 228 ppi
  • Samsung Galaxy SIII: 720x1280px, 306 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, involving multiple shapes, buttons, bitmaps and more.

The interface graphic resources necessary for this tutorial can be found in the attached download. The graphics are from openclipart.org.


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 to save them in your project folder.


Step 5: 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 6: Main.lua

Let's write the application!

Open your prefered Lua editor (any Text Editor will work, but some may not provide Lua syntax highlighting) and prepare to write your awesome app. Remember to save the file as main.lua in your project folder.


Step 7: 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.

Necesary Classes

Variables and Constants

Declare Functions

    contructor (Main function)
	
    class methods (other functions)

call Main function

Step 8: Hide the 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 9: Import Physics

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

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

Step 10: 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 11: The Title View

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

-- [Title View]

local titleBg
local playBtn
local creditsBtn
local titleView

Step 12: 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 13: The Info Bar

This image will be placed on top of our previous background. This will be our info bar which will display the current score and time remaining.


Step 14: Apple

The apple graphic. These will be generated on enter frame and placed at a random position.


Step 15: Stick

The stick graphic. It will be added using the same method as the apple. This item decreases the score when grabbed.


Step 16: The Basket

The basket will be used to collect the falling items.

-- Basket

local basket

Step 17: Alert

This is the alert that will be displayed when the time is over. It will reveal the score and end the game.


Step 18: Variables

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

-- Variables

local infoBar
local timerSrc
local timeLeft
local times = 0 -- increased to 2 on update timer function(500) to count a second
local score

Step 19: Declare Functions

Declare all functions as local at the start.

-- Functions

local Main = {}
local startButtonListeners = {}
local showCredits = {}
local hideCredits = {}
local showGameView = {}
local gameListeners = {}
local dragBasket = {}
local update = {}
local onCollision = {}

Step 20: Constructor

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

function Main()
	-- code...
end

Step 21: 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', 20.5, 130.5)
	playBtn = display.newImage('playBtn.png', display.contentCenterX + 115, display.contentCenterY + 16)
	creditsBtn = display.newImage('creditsBtn.png', 5, display.contentHeight - 57)
	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 items creation, 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!

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