Added a simple Pong game example to IDE Lua examples.

Examples/Lua/Game_Demos/Pong/Pong.polyproject

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+<?xml version="1.0" ?>
+<PolycodeProject defaultWidth="640" defaultHeight="480" antiAliasingLevel="0" entryPoint="Scripts/Main.lua" textureFiltering="linear" vSync="true" anisotropyLevel="0" frameRate="60">
+    <backgroundColor red="0.167291" green="0.217107" blue="0.240642" />
+    <polyarray:packedItems>
+        <item type="folder" path="Resources" />
+        <item type="folder" path="Scripts" />
+    </polyarray:packedItems>
+</PolycodeProject>

Examples/Lua/Game_Demos/Pong/Scripts/Main.lua

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+------------------------------------------------
+-- Polycode Pong example by Ivan Safrin, 2013
+------------------------------------------------
+
+-- create a new Screen and set its height to 480
+screen = PhysicsScreen(1.0, 30)
+screen:setNormalizedCoordinates(true, 480)
+
+-- load the playing field from the entity file and add it to the screen
+field = ScreenEntityInstance("Resources/field.entity2d")
+screen:addChild(field)
+
+-- get a handle to the player paddles and ball in the screen file and begin tracking collision
+
+ball = field:getScreenEntityById("ball", true)
+screen:trackCollisionChild(ball, PhysicsScreenEntity.ENTITY_RECT)
+
+p1 = field:getScreenEntityById("p1", true)
+screen:trackCollisionChild(p1, PhysicsScreenEntity.ENTITY_RECT)
+
+p2 = field:getScreenEntityById("p2", true)
+screen:trackCollisionChild(p2, PhysicsScreenEntity.ENTITY_RECT)
+
+topWall = field:getScreenEntityById("topWall", true)
+screen:trackCollisionChild(topWall, PhysicsScreenEntity.ENTITY_RECT)
+
+bottomWall = field:getScreenEntityById("bottomWall", true)
+screen:trackCollisionChild(bottomWall, PhysicsScreenEntity.ENTITY_RECT)
+
+--load sounds
+hitSound = Sound("Resources/hit.wav")
+scoreSound = Sound("Resources/score.wav")
+
+ballSpeed = 400.0
+ballDirection = Vector2(1.0, 0.0)
+
+-- initialize scores and get references to the player score labels on the field
+p1scoreLabel = cast(field:getScreenEntityById("p1scoreLabel", true), ScreenLabel)
+p2scoreLabel = cast(field:getScreenEntityById("p2scoreLabel", true), ScreenLabel)
+p1Score = 0
+p2Score = 0
+
+function onCollision(t, event)
+	-- we need to cast the event to PhysicsScreenEvent because this is a PhysicsScreen event
+	physicsEvent = cast(event, PhysicsScreenEvent)
+
+	-- check if the colliding entity is the ball
+	if same_c_class(physicsEvent:getFirstEntity(), ball) then
+
+		-- if colliding with player 1 or player 2 paddle
+		if same_c_class(physicsEvent:getSecondEntity(), p1) or  same_c_class(physicsEvent:getSecondEntity(), p2) then
+
+			-- reverse the horizontal direction
+			ballDirection.x = ballDirection.x * -1 
+
+			-- adjust the vertical direction based on where on the paddle it hit
+			ballDirection.y = (ball.position.y - physicsEvent:getSecondEntity().position.y)/80.0
+			if ballDirection.y > 1.0 then ballDirection.y = 1.0 end
+			if ballDirection.y < -1.0 then ballDirection.y = -1.0 end
+		else
+			-- if collliding with the walls, simply reverse the vertical direction
+			ballDirection.y = ballDirection.y * -1
+		end
+
+		-- play the hit sound
+		hitSound:Play()
+	end
+end
+
+-- add a collision listener to the Physics Screen
+-- onCollision will now be called every time there is a collion between
+-- entities that we are tracking
+screen:addEventListener(nil, onCollision, PhysicsScreenEvent.EVENT_NEW_SHAPE_COLLISION)
+
+-- Update is called automatically every frame
+function Update(elapsed)
+
+	-- check player 1 input
+	if Services.Input:getKeyState(KEY_a) == true then
+		p1.position.y = p1.position.y - (300 * elapsed)
+	elseif Services.Input:getKeyState(KEY_z) == true then
+		p1.position.y = p1.position.y + (300 * elapsed)
+	end
+
+	-- check player 2 input
+	if Services.Input:getKeyState(KEY_UP) == true then
+		p2.position.y = p2.position.y - (300 * elapsed)
+	elseif Services.Input:getKeyState(KEY_DOWN) == true then
+		p2.position.y = p2.position.y + (300 * elapsed)
+	end
+
+	-- limit the paddle positions so they don't go offscreen
+	if p1.position.y < -180 then p1.position.y = -180 end
+	if p1.position.y > 180 then p1.position.y = 180 end
+	if p2.position.y < -180 then p2.position.y = -180 end
+	if p2.position.y > 180 then p2.position.y = 180 end
+
+	-- update the ball position
+	ball.position.x = ball.position.x + (ballDirection.x * ballSpeed * elapsed)
+	ball.position.y = ball.position.y + (ballDirection.y * ballSpeed * elapsed)
+
+	-- check if the ball beyond player 1's paddle and increment player 2's score
+	if ball.position.x < -328 then
+		ball.position.x = -200
+		ball.position.y = 0
+		ballDirection.x = 1.0
+		ballDirection.y = 0.0
+		scoreSound:Play()
+		p2Score = p2Score + 1
+		p2scoreLabel:setText(""..p2Score)
+	end
+
+	-- check if the ball beyond player 2's paddle and increment player 1's score
+	if ball.position.x > 328 then
+		ball.position.x = 200
+		ball.position.y = 0
+		ballDirection.x = -1.0
+		ballDirection.y = 0.0
+		scoreSound:Play()
+		p1Score = p1Score + 1
+		p1scoreLabel:setText(""..p1Score)
+	end
+
+end