Emanuele Feronato

var game

var gameOptions = {

     // game width
     gameWidth: 640,
     
     // game height
     gameHeight: 960,
     
     // number of segments which build the tail
     tailSegments: 300,
     
     // lenght of each segment
     segmentLength: 2     
}

// when the window loads
window.onload = function() {
    
     // game creation	
	game = new Phaser.Game(gameOptions.gameWidth, gameOptions.gameHeight);
     
     // adding game state
     game.state.add("TheGame", TheGame);
     
     // starting game state
     game.state.start("TheGame");
}

var TheGame = function(){};

TheGame.prototype = {

     // when the state preloads
     preload: function(){
     
          // setting the game on maximum scale mode to cover the entire screen
          game.scale.scaleMode = Phaser.ScaleManager.SHOW_ALL;
          game.scale.pageAlignHorizontally = true;
          game.scale.pageAlignVertically = true;
          
          // preloading maze image, a PNG image with transparency
          game.load.image("maze", "assets/sprites/maze.png");
     },
     
     // once the state has been created
     create: function(){
          
          // creation of a bitmap data with the same size as the game
          this.bitmap = game.make.bitmapData(game.width, game.height);
          
          // drawing "maze" image on the bitmap data
          this.bitmap.draw("maze");
          
          // updating bitmap data to let it have actual image data
          this.bitmap.update();
          
          // adding the bitmap data as a sprite
          game.add.sprite(0, 0, this.bitmap);  
          
          // segments is the array which will contain string segments
          this.segments = [];
          
          // populating segments array with gameOptions.tailSegments Point
          for(var i = 0; i < gameOptions.tailSegments; i++){
               this.segments[i] = new Phaser.Point(0, 0);
          } 
          
          // we create a graphics instance called "canvas", we'll draw the string on it
          this.canvas = game.add.graphics(0, 0);  
     },
     
     // at each update
     update: function(){
     
          // clearing the canvas, ready to be redrawn
          this.canvas.clear();
          
          // setting line style to a 4 pixel thick line, red, 100% opaque
          this.canvas.lineStyle(4, 0x00ff00, 1);
          
          // the head of the string is current input position
          var head = new Phaser.Point(game.input.x, game.input.y);
          
          // placing the pen on the head
          this.canvas.moveTo(head.x, head.y);
          
          // the first segment is the head itself
          this.segments[0] = new Phaser.Point(head.x, head.y);
          
          // looping through all segments starting from the second one
          for(var i = 1; i < gameOptions.tailSegments - 1; i++){
          
               // determining the angle between current segment and previous segment
               var nodeAngle = Math.atan2(this.segments[i].y - this.segments[i - 1].y, this.segments[i].x - this.segments[i - 1].x);
               
               // calculating new segment position according to previous segment position and the angle
               this.segments[i] = new Phaser.Point(this.segments[i - 1].x + gameOptions.segmentLength * Math.cos(nodeAngle), this.segments[i - 1].y + gameOptions.segmentLength * Math.sin(nodeAngle));
               
               // getting the color behind the segment
               var color = this.bitmap.getPixelRGB(Math.round(this.segments[i].x), Math.round(this.segments[i].y));
               
               // if the color alpha is different than zero, that is it's not a transparent pixel...
               if(color.a != 0){
               
                    // from now on, draw the string in red
                    this.canvas.lineStyle(4, 0xff0000, 1);
               } 
               
               // drawing the segment
               this.canvas.lineTo(this.segments[i].x, this.segments[i].y);    
          }
     }
}