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Corona SDK

Create a Cut the Rope Inspired Game - Interface Creation

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In this tutorial series, you’ll learn how to create a Cut the Rope inspired game. The objective of the game is to cut the rope holding the bone and feed the mascot. Read on!


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 cut the rope holding the bone using a swipe gesture to feed the dog. 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 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, this involves multiple shapes, buttons, bitmaps and more.

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

This image will be placed on top of our previous background. This will be our instructions message.

-- Instructions

local ins

Step 14: Dog

The dog graphic. This will be placed in the stage at the bottom-center position.

-- Dog

local dog

Step 15: Stars Shadow

The stars shadow images are used to represent how many stars are left to grab.

-- Shadow Stars

local s1
local s2
local s3

Step 16: Hanger

The hanger that holds the rope.

-- Hang

local hang

Step 17: Alert

This is the alert that will be displayed when the game is over. It will complete the level and end the game.


Step 18: Sounds

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 bite.


Step 19: Variables

This 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 view 
local ropeParts = display.newGroup()
local initX -- initial X position of the line drawn by the finger
local initY
local lines = display.newGroup()
local line
local collected = 0 -- current collected stars

-- Levels, dynamically created using a multidimensional table and a for loop
-- the 0's are empty spaces
-- 1 is the hanger
-- and the 2's are the stars

local l1 = {{0, 0, 0, 0, 1, 0, 0, 0, 0, 0},
			{0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
			{0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
			{0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
			{0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
			{0, 0, 0, 0, 2, 0, 0, 0, 0, 0},
			{0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
			{0, 0, 0, 0, 2, 0, 0, 0, 0, 0},
			{0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
			{0, 0, 0, 0, 2, 0, 0, 0, 0, 0},}

Step 19: Declare Functions

Declare all functions as local at the start.

-- Functions

local Main = {}
local startButtonListeners = {}
local showCredits = {}
local hideCredits = {}
local showGameView = {}
local loadLevel = {}
local gameListeners = {}
local drawLine = {}
local ropeCollision = {}
local starDogCollision = {}
local alert = {}

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', 40, 57)
	playBtn = display.newImage('playBtn.png', 125, 225)
	creditsBtn = display.newImage('creditsBtn.png', 115, 286)
	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 level 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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