Emanuele Feronato

// the game itself
var game;

// when the window loads...
window.onload = function() {
     // creation of a new Phaser.Game instance. Width: 320px, height: 640px;	
	game = new Phaser.Game(320, 640);
     // creation of a new Phaser state called "PlayGame"
	game.state.add("PlayGame", playGame)
     // starting "PlayGame" state;
	game.state.start("PlayGame");	
}

// PlayGame state
var playGame = function(game){}
playGame.prototype = {
	preload: function(){
          // loading the sprite sheet with all platforms
          game.load.spritesheet("platforms", "platforms.png", 346, 258);     	
	},
	create: function(){
          // placing seven platforms on the canvas
          for(var i = 0; i < 7; i++){
               addPlatform(i, game.rnd.between(0, 2));     
          }
	}
}

// addPlatform function, the core of the script. Arguments: posY -> vertical position; size -> platform size
function addPlatform(posY, size){
     // array with possible platform colors
     var platformColors = ["0xff0000", "0x00ff00", "0x0000ff", "0xffff00", "0xff00ff", "0x00ffff"];
     // minimum delay between the creation of the current platform and the creation of next platform, according to platform size.
     // index recap
     // 0: minimum delay after a one-sized platform
     // 1: min delay after a two-sized platform
     // 2: min delay after a three-sized platform
     var delayArray = [520, 840, 1160];    
     // this array contains the x and y coordinates of the initial and final platform position
     // index recap
     // 0 start x coordinate
     // 1 start y coordinate
     // 2 end x coordinate
     // 3 end y coordinate
     var startEndArray = [500, -300 + posY * 120, 500 - 800 * Math.cos(Math.PI/6), -300 + posY * 120 + 800 * Math.sin(Math.PI/6)];
     // startX is startEndArray[0] or startEndArray[2] according to posY value
     var startX = startEndArray[0 + 2 * (posY % 2)];
     // startY is startEndArray[1] or startEndArray[3] according to posY value
     var startY = startEndArray[1 + 2 * (posY % 2)];
      // endX is startEndArray[0] or startEndArray[2] according to posY value
     var endX = startEndArray[2 - 2 * (posY % 2)];
     // endY is startEndArray[1] or startEndArray[3] according to posY value
     var endY = startEndArray[3 - 2 * (posY % 2)]; 
     // placing the platform itself
     var platform = game.add.sprite(startX, startY, "platforms");
     // showing the proper frame
     platform.frame = size;
     // scaling the platform
     platform.scale.setTo(0.5); 
     // tinting the platform with a random color
     platform.tint = platformColors[game.rnd.between(0, platformColors.length-1)];
      // determining next platform size
     var nextPlatform = game.rnd.between(0, 2);  
     // tween to make the platform move from the starting point to the end point 
     var platformTween = game.add.tween(platform).to({
          x: endX,
          y: endY,
     }, 5000, Phaser.Easing.Linear.None, true);
     // when the easing is complete, then destroy the platform
     platformTween.onComplete.add(function(p){
          p.destroy();
     })
     // wait for the minimum delay + a random delay before placing another platform.
     // the way I choose the delay from delayArray varies according to platform direction
     if(posY % 2 == 0){
          game.time.events.add(delayArray[platform.frame] + game.rnd.between(100, 250), function(){
               addPlatform(posY, nextPlatform);
          });
     }
     else{
          game.time.events.add(delayArray[nextPlatform] + game.rnd.between(100, 250), function(){
               addPlatform(posY, nextPlatform);
          });     
     }
}