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Create a Retro Racing Game - Interface Creation

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In this tutorial series, you'll learn how to create a Retro Racing game. The objective of the game is to get to the finish line without hitting an obstacle. Read on!


Also available in this series:

  1. Create a Retro Racing Game - Interface Creation
  2. Create a Retro Racing Game - Adding Interaction

Step 1: Application Overview

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

The player will be able to control a racing car to avoid obstacles, 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/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.


Step 3: Interface

A simple and friendly interface will be used that 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: 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.


Necessary 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()
physics.setGravity(0,0)

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: Game Background

This image will be placed on top of our previous background. This will be the game background.

-- Game Background

local gameBg

Step 14: Car

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

-- Car

local car

Step 15: Highway

The highway lines are used to represent the moving road.

-- Highway Lines

local lines1
local lines2

Step 16: Obstacles

You have to avoid these the pass the level.

-- Obstacles

local obstacles

Step 17: TextFields

Used to display the current game information such as Score, Level and Speed.

-- TextFields

local score
local level
local speed

Step 18: Alert

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

-- Alert

local alertView

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 tween the credits view
local moveTimer --this timer handles the objects movement
local leftBtn
local rightBtn
local oTimer -- obstacle timer
local positionsTable = {36, 90, 144} --available x positions for obstacles
local started --true if the first obstacle has been created

Step 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 moveCar = {}
local addObstacle = {}
local update = {}
local onCollision = {}
local alert = {}

Step 21: Constructor

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

function Main()
	-- code...
end

Step 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()
	titleBg = display.newImage('titleBg.png', 70, 50)
	playBtn = display.newImage('playBtn.png', 119, 222)
	creditsBtn = display.newImage('creditsBtn.png', 85, 282)
	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!

Read Part Two of this Series

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