Build an Apple Catcher Game - Adding Interaction

This is the second installment in our Corona SDK Apple Catcher tutorial. In today's tutorial, we'll add to our interface by creating the game interaction. Read on!

Also available in this series:

Build an Apple Catcher Game - Interface Creation
Build an Apple Catcher Game - Adding Interaction

Where We Left Off. . .

Please be sure to check part 1 of the series to fully understand and prepare for this tutorial.

Step 1: Start Button Listeners

This function adds the necesary listeners to the TitleView buttons.

function startButtonListeners(action)
	if(action == 'add') then
		titleBg:addEventListener('tap', showGameView)
		creditsBtn:addEventListener('tap', showCredits)
	else
		titleBg:removeEventListener('tap', showGameView)
		creditsBtn:removeEventListener('tap', showCredits)
	end
end

Step 2: 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)
	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

Step 3: Hide Credits

When the credits screen is tapped, it'll be tweened out of the stage and removed.

function hideCredits:tap(e)
	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

Step 4: Show Game View

When the Start 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})

Step 5: Add Basket

This code places the basket on the stage.

-- Basket
basket = display.newImage('basket.png', 203, 240)

Step 6: Info Bar

Next we add the Info Bar image and create the corresponding TextFields that will display the current score and time remaining.

-- Info Bar
	
infoBar = display.newImage('infoBar.png', 280)
score = display.newText('0', 65, -2, native.systemFontBold, 14)
score:setTextColor(0)
timeLeft = display.newText('20', 175, -2, native.systemFontBold, 14)
timeLeft:setTextColor(0)

Step 7: Add Physics

Now we add physics to the basket and call the function that will add the game listeners.

-- Add Physics
	
physics.addBody(basket, 'static')

-- Game Listeners
	
gameListeners('add')

Step 8: Game Listeners

This function adds the necessary listeners to start the game logic.

function gameListeners(action)
	if(action == 'add') then
		timerSrc = timer.performWithDelay(500, update, 0)
		basket:addEventListener('collision', onCollision)
		basket:addEventListener('touch', dragBasket)
	else
		timer.cancel(timerSrc)
		timerSrc = nil
		basket:removeEventListener('collision', onCollision)
		basket:removeEventListener('touch', dragBasket)
		physics.stop()
	end
end

Step 9: Drag Basket

The following code uses the phase event property to drag the basket on the x-axis using the player's finger.

-- Drag Basket

function dragBasket(e)
	if(e.phase == 'began') then
		lastX = e.x - basket.x
	elseif(e.phase == 'moved') then
		basket.x = e.x - lastX
	end
end

Step 10: Add Apple or Stick

The update function is executed every half second. Each time a random number is generated and then tested to see if an apple or a stick will be added to the stage. The item is then added to the physics engine and pulled down by gravity automatically.

function update(e)
	-- Add Apple or Stick
	
	local rx = math.floor(math.random() * display.contentWidth)
	local r = math.floor(math.random() * 4) -- 0, 1, 2, or 3 (3 is stick)
	
	if(r == 3) then
		local stick = display.newImage('stick.png', rx, -20)
		stick.name = 'stick'
		physics.addBody(stick)
	else
		local apple = display.newImage('apple.png', rx, -40)
		apple.name = 'apple'
		physics.addBody(apple)
	end

Step 11: Decrease Timer

Here we increase the timer variable by one every half second so when it is equal to 2, a second is decreased from the timeLeft textfield.

-- Decrease Timer
	
times = times + 1
if(times == 2) then
	timeLeft.text = tostring(tonumber(timeLeft.text) - 1)
	times = 0
end

Step 12: Check for Timer Completion

This part checks if the time available is over and calls an alert if so.

	-- Check if timer is over
	
	if(timeLeft.text == '0') then
		alert()
	end
end

Step 13: Apple Collision

When an apple hits the basket it is removed from the stage, the score is updated, and an animation is showed displaying the amount of score raised.

function onCollision(e)
	if(e.other.name == 'apple') then
		-- Remove Apple
		display.remove(e.other)
		-- Display animation
		local scoreAnim = display.newText('+10', basket.x, basket.y-10, native.systemFontBold, 16)
		transition.to(scoreAnim, {time = 600, y = scoreAnim.y - 30, alpha = 0, onComplete = function() display.remove(scoreAnim) scoreAnim = nil end})
		-- Update Score
		score.text = tostring(tonumber(score.text) + 10)

Step 14: Stick Collision

This uses the same method as the last step, this time decreasing the score.

elseif(e.other.name == 'stick') then
		--Remove Stick
		display.remove(e.other)
		-- Display animation
		local scoreAnim = display.newText('-10', basket.x, basket.y-10, native.systemFontBold, 16)
		transition.to(scoreAnim, {time = 600, y = scoreAnim.y - 30, alpha = 0, onComplete = function() display.remove(scoreAnim) scoreAnim = nil end})
		-- Update Score
		score.text = tostring(tonumber(score.text) - 10)
	end
end

Step 15: Alert

This function will stop the game and display the final score using the alert background and tweening it.

function alert()
	gameListeners('remove')
	local alertView = display.newImage('alert.png', 110, 74)
	transition.from(alertView, {time = 300, xScale = 0.5, yScale = 0.5})
	local totalScore = display.newText(score.text, display.contentCenterX-11, display.contentCenterY + 24, native.systemFontBold, 21)
	totalScore:setTextColor(72, 34, 0)
end

Step 16: 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()

Step 17: 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 compliler.

Step 18: 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.

Step 19: Testing in 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!

Step 20: 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

Experiment with the final result and try to make your own custom version of the game!

I hope you liked this tutorial series and found it helpful. Thank you for reading!

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