In this tutorial series, I'll be showing you how to create an infinite scroller game with the Corona SDK by building an Ostrich Runner game. You'll learn about scrolling objects, physics manipulation, touch controls, and collision detection. The objective of the game is to move the character and collect items to raise the score. Read on!
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 use the touch screen on the device to move the character and to collect items. You can modify the parameters in the code to customize the game.
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 S III: 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. The interface will involve multiple shapes, buttons, bitmaps, and more.
The interface graphic resources necessary for this tutorial can be found in the attached download.
4. Export Graphics
Depending on the device you have selected, you may need to export the graphics in the recommended PPI. You can do this using 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.
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
Now 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.
Necesary Classes
Variables and Constants
Declare Functions
contructor (Main function)
class methods (other functions)
call Main function
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.
9. Import Physics
We'll use the Physics library to handle collisions. Use this code to import it:
-- Physics
local physics = require('physics')
physics.start()
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
This is the Title View, it will be the first interactive screen to appear in our game. These variables store the components:
-- [Title View] local title local playBtn local creditsBtn local titleView
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
13. Game Background
The level background, it also adds the score textfield.
-- Game Background local gameBg
14. Instructions Message
An instructions message will appear at the start of the game, it will be tweened out after 2 seconds.
-- Instructions local ins
15. Character
The character graphic. The objective of the game is to move it up and down in the screen in order to collect the cherries.
-- Ostrich local ostrich
16. Cherries
The cherry graphic. There are also bad cherries that will make you lose the game.
-- Cherrys local cherrys
17. Pad
The pad graphics. Tap on them to move the character.
-- Pad local up local down
18. Alert
This is the alert that will be displayed when a bad cherry is collected. It will complete the level and end the game.
-- Alert local alertView
19. Sounds
We'll use Sound Effects to enhance the feeling of the game, you can find the music used in this example on playonloop.com. The sounds were created in as3sfxr.
-- Sounds
local bgMusic = audio.loadStream('POL-purple-hills-short.mp3')
local cherrySnd = audio.loadSound('cherry.mp3')
local badCherrySnd = audio.loadSound('badCherry.mp3')
20. Variables
These are the variables we'll use. Read the comments in the code to learn more about them.
-- Variables
local timerSrc -- add cherry timer
local yPos = {108, 188, 268} -- possible ostrich y positions
local speed = 5 -- cherry speed
local speedTimer -- timer to change speed of the cherrys
21. Declare Functions
Declare all functions as local at the start.
-- Functions
local Main = {}
local startButtonListeners = {}
local showCredits = {}
local hideCredits = {}
local showGameView = {}
local gameListeners = {}
local startGame = {}
local createCherry = {}
local movePlayer = {}
local increaseSpeed = {}
local update = {}
local onCollision = {}
local alert = {}
22. Constructor
Next we'll create the function that will initialize all the game logic:
function Main() -- code... end
23. 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('title.png', 113, 43)
playBtn = display.newImage('playBtn.png', 219, 160)
creditsBtn = display.newImage('creditsBtn.png', 205, 223)
titleView = display.newGroup(bg, titleBg, playBtn, creditsBtn)
startButtonListeners('add')
end
24. Start Button Listeners
This function adds the necessary 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
25. 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', -130, display.contentHeight-140)
transition.to(creditsView, {time = 300, x = 65, onComplete = function() creditsView:addEventListener('tap', hideCredits) end})
end
26. 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
27. Show Game View
When the Play button is tapped, the title view is tweened and removed, revealing the game view. There are many parts involved in this view, so we'll split them in the next steps.
function showGameView:tap(e)
transition.to(titleView, {time = 300, x = -titleView.height, onComplete = function() startButtonListeners('rmv') display.remove(titleView) titleView = nil end})
28. Instructions Message
The following lines add the game instructions.
-- Instructions Message
ins = display.newImage('ins.png', 187, 199)
29. Score TextField
This part creates the Score TextField on the stage.
-- TextFields
scoreTF = display.newText('0', 258, 26.5, 'Marker Felt', 16)
scoreTF:setTextColor(184, 165, 104)
30. Ostrich
Add the ostrich character to the level.
-- Ostrich
ostrich = display.newImage('ostrich.png', 11, 180)
31. Pad
These are the on screen controls for the game.
-- Pad
up = display.newImage('up.png', 418, 20)
down = display.newImage('down.png', 418, 258)
up.name = 'up'
down.name = 'down'
32. Physics
Next, we add physics to the game objects. We also create a Table for the cherries and call the gameListeners function.
-- Add Ostrich Physics
physics.addBody(ostrich)
ostrich.isSensor = true
cherrys = display.newGroup()
gameListeners('add')
end
33. Game Listeners
This function adds the necessary listeners to start the game logic.
function gameListeners(action)
if(action == 'add') then
ins:addEventListener('tap', startGame)
Runtime:addEventListener('enterFrame', update)
up:addEventListener('tap', movePlayer)
down:addEventListener('tap', movePlayer)
speedTimer = timer.performWithDelay(5000, increaseSpeed, 5)
else
Runtime:removeEventListener('enterFrame', update)
up:removeEventListener('tap', movePlayer)
down:removeEventListener('tap', movePlayer)
timer.cancel(timerSrc)
timerSrc = nil
timer.cancel(speedTimer)
speedTimer = nil
end
end
34. Start Game
In this part, we remove the instructions message, start playing the game background music, and create a timer that will add a cherry every 400 milliseconds.
function startGame()
ins:removeEventListener('tap', startGame)
display.remove(ins)
audio.play(bgMusic, {loops = -1, channel = 1})
timerSrc = timer.performWithDelay(400, createCherry, 0)
end
35. Create Cherry
The next snippet of code creates a regular or bad cherry based on a random number and places it on the screen. The resulting object is added to the physics engine to check for collisions.
function createCherry()
local cherry
local rnd = math.floor(math.random() * 4) + 1
if(rnd == 4) then
cherry = display.newImage('badCherry.png', display.contentWidth, yPos[math.floor(math.random() * 3)+1])
cherry.name = 'bad'
else
cherry = display.newImage('cherry.png', display.contentWidth, yPos[math.floor(math.random() * 3)+1])
cherry.name = 'cherry'
end
-- Cherry physics
physics.addBody(cherry)
cherry.isSensor = true
cherry:addEventListener('collision', onCollision)
cherrys:insert(cherry)
end
36. Move Player
We change the Y position of the Ostrich using the control pad we created earlier.
function movePlayer(e) if(e.target.name == 'up' and ostrich.y ~= 122) then ostrich.y = ostrich.y - 80 elseif(e.target.name == 'down' and ostrich.y ~= 282) then ostrich.y = ostrich.y + 80 end end
37. Increase Speed
A timer will increase the speed every 5 seconds. An icon is displayed to alert the player of the speed change.
function increaseSpeed()
speed = speed + 2
-- Icon
local icon = display.newImage('speed.png', 204, 124)
transition.from(icon, {time = 200, alpha = 0.1, onComplete = function() timer.performWithDelay(500, function() transition.to(icon, {time = 200, alpha = 0.1, onComplete = function() display.remove(icon) icon = nil end}) end) end})
end
38. Update Function
This function handles the cherries movement. It uses the speed variable to determine how many pixels to move the cherry every frame.
function update() if (cherrys ~= nil) then for i = 1, cherrys.numChildren do cherrys[i].x = cherrys[i].x - speed end end end
39. Collisions
Now we check if the cherry collides with the Ostrich using the following code. The score raises when a regular cherry collides and an alert is called when a bad cherry is touched. In both cases the cherry is removed and a sound is played.
function onCollision(e)
e.target:removeEventListener('collision', onCollision)
display.remove(e.target)
if(e.target.name == 'cherry') then
--Score
scoreTF.text = tostring(tonumber(scoreTF.text) + 50)
audio.play(cherrySnd)
-- Bad cherry
elseif(e.target.name == 'bad') then
audio.play(badCherrySnd)
alert()
end
end
40. Alert
The alert function creates an alert view, animates it, and then ends the game.
function alert()
audio.stop(1)
audio.dispose()
bgMusic = nil
gameListeners('rmv')
alertView = display.newImage('alert.png', 160, 115)
transition.from(alertView, {time = 300, xScale = 0.5, yScale = 0.5})
local score = display.newText(scoreTF.text, (display.contentWidth * 0.5) - 12, (display.contentHeight * 0.5) + 5, 'Marker Felt', 18)
score:setTextColor(184, 165, 104)
-- Wait 100 ms to stop physics
timer.performWithDelay(1000, function() physics.stop() end, 1)
end
41. Call Main Function
In order to start the game, the Main function needs to be called. With the above code in place, we'll do that here:
Main()
42. Loading Screen
The Default.png file is an image that will be displayed right when you start the application while the iOS loads the basic data to show the Main Screen. Add this image to your project source folder, it will be automatically added by the Corona compiler.
43. Icon
Using the graphics you created before, you can now create a nice and good looking icon. The icon size for the non-retina iPhone icon is 57x57px, but the retina version is 114x114px and the iTunes store requires a 512x512px version. I suggest creating the 512x512 version first and then scaling down for the other sizes.
It doesn't need to have the rounded corners or the transparent glare, iTunes and the iPhone will do that for you.
44. Testing in the Simulator
It's time to do the final test. Open the Corona Simulator, browse to your project folder, and then click open. If everything works as expected, you are ready for the final step!
45. Build
In the Corona Simulator, go to File > Build and select your target device. Fill the required data and click build. Wait a few seconds and your app will be ready for device testing and/or submission for distribution!
Conclusion
In this series, we've learned about physics behavior, tap listeners, and collisions. These skills can be really useful in a wide number of games!
Experiment with the final result and try to make your custom version of the game!
I hope you liked this tutorial and find it helpful. Thank you for reading!
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