Corona sdk: build a frogger inspired game – interface creation

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In this tutorial series, I'll be showing you how to create a Frogger Inspired game with the Corona SDK. You'll learn about moving objects across the screen and detect when they are colliding using the physics engine. The objective of the game is to move the Frog on the stage to its containers without being hit by an obstacle. Read on!

1. Application Overview

App 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 use the on-screen pad to move the frog and get it to the other side, you can modify the parameters in the code to customize the game.

2. Target Device

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/Mini: 1024x768px, 132 ppi
  • iPad Retina: 2048x1536, 264 ppi
  • iPhone/iPod Touch: 320x480px, 163 ppi
  • iPhone/iPod Retina: 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.

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.

Frogger Sprite Pack.

4. Export Graphics

Export Graphics

Depending on the device you have selected, you may need to export the graphics in the recommended PPI. You can do this 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.

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"

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.

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.

Necessary Classes

Variables and Constants

Declare Functions

    contructor (Main function)
    class methods (other functions)

call Main function

8. Hide Status Bar


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.

9. Import Physics

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

-- Physics

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

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')

11. Title View

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 title
local playBtn
local creditsBtn
local titleView

12. Credits View

Credits View

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

-- [CreditsView]

local creditsView

13. Game Background

Game Background

This image will replace our previous background. This will be the game background.

-- Game Background

local gameBg

14. Frog


The frog you will be able to control.

-- Frog

local frog

15. Pad

Place Holders

This is the on-screen pad used to move the frog around the level.

-- [Pad]

local up
local left
local down
local right

16. Cars


The obstacles the player needs to avoid to cross to the other side.

17. Alert


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

  -- Alert
  local alertView

18. Sounds


We'll use Sound Effects to enhance the feeling of the game, the sounds used in this app were generated by AS3SFXR.

-- Sounds

local moveSnd = audio.loadSound('move.mp3')
local loseSnd = audio.loadSound('lose.mp3')
local goalSnd = audio.loadSound('goal.mp3')

19. Variables

This are the variables we'll use. Read the comments in the code to learn more about them.

-- Variables

local lastY --Used to reposition the titleView after credits tween
local obstacles --Obstacles group
local counter = 0 --Counts the frogs that had crossed the street

20. Declare Functions

Declare all functions as local at the start.

-- Functions

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

21. Constructor

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

function Main()
	-- code...

22. 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()
	title = display.newImage('title.png', 64, 130)
	playBtn = display.newImage('playBtn.png', 134, 245)
	creditsBtn = display.newImage('creditsBtn.png', 114, 305)
	titleView = display.newGroup(bg, title, playBtn, creditsBtn)

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. Read the final part!

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