Emanuele Feronato

var game;
var speedMult = 0.7;
// this is the friction which will slow down the map. Must be less than 1
var friction = 0.99;

window.onload = function() {	
	game = new Phaser.Game(480, 480, Phaser.AUTO, "");
     game.state.add("PlayGame", playGame);
     game.state.start("PlayGame");
}

var playGame = function(game){};
playGame.prototype = {
     preload: function(){
          game.load.image("map", "map.png");
     },
     create: function(){  
          // the big map to scroll
          this.scrollingMap = game.add.image(0, 0, "map");
          // map will accept inputs
          this.scrollingMap.inputEnabled = true;
          // map can be dragged
          this.scrollingMap.input.enableDrag(false);
          // custom property: we save map position
          this.scrollingMap.savedPosition = new Phaser.Point(this.scrollingMap.x, this.scrollingMap.y);
          // custom property: the map is not being dragged at the moment
          this.scrollingMap.isBeingDragged = false; 
          // custom property: map is not moving (or is moving at no speed)
          this.scrollingMap.movingSpeed = 0; 
          // map can be dragged only if it entirely remains into this rectangle
          this.scrollingMap.input.boundsRect = new Phaser.Rectangle(game.width - this.scrollingMap.width, game.height - this.scrollingMap.height, this.scrollingMap.width * 2 - game.width, this.scrollingMap.height * 2 - game.height);
          // when the player starts dragging...
          this.scrollingMap.events.onDragStart.add(function(){
               // set isBeingDragged property to true
               this.scrollingMap.isBeingDragged = true;
               // set movingSpeed property to zero. This will stop moving the map
               // if the player wants to drag when it's already moving
               this.scrollingMap.movingSpeed = 0;
          }, this);
          // when the player stops dragging...
          this.scrollingMap.events.onDragStop.add(function(){
               // set isBeingDragged property to false
               this.scrollingMap.isBeingDragged = false;
          }, this);
     },
     update:function(){
          // if the map is being dragged...
          if(this.scrollingMap.isBeingDragged){
               // save current map position
               this.scrollingMap.savedPosition = new Phaser.Point(this.scrollingMap.x, this.scrollingMap.y);
          }
          // if the map is NOT being dragged...
          else{
               // if the moving speed is greater than 1...
               if(this.scrollingMap.movingSpeed > 1){
                    // adjusting map x position according to moving speed and angle using trigonometry
                    this.scrollingMap.x += this.scrollingMap.movingSpeed * Math.cos(this.scrollingMap.movingangle);
                    // adjusting map y position according to moving speed and angle using trigonometry
                    this.scrollingMap.y += this.scrollingMap.movingSpeed * Math.sin(this.scrollingMap.movingangle);
                    // keep map within boundaries
                    if(this.scrollingMap.x < game.width - this.scrollingMap.width){
                         this.scrollingMap.x = game.width - this.scrollingMap.width;
                    }
                    // keep map within boundaries
                    if(this.scrollingMap.x > 0){
                         this.scrollingMap.x = 0;
                    }
                    // keep map within boundaries
                    if(this.scrollingMap.y < game.height - this.scrollingMap.height){
                         this.scrollingMap.y = game.height - this.scrollingMap.height;
                    }
                    // keep map within boundaries
                    if(this.scrollingMap.y > 0){
                         this.scrollingMap.y = 0;
                    }
                    // applying friction to moving speed
                    this.scrollingMap.movingSpeed *= friction;
                    // save current map position
                    this.scrollingMap.savedPosition = new Phaser.Point(this.scrollingMap.x, this.scrollingMap.y);
               }
               // if the moving speed is less than 1...
               else{
                    // checking distance between current map position and last saved position
                    // which is the position in the previous frame
                    var distance = this.scrollingMap.savedPosition.distance(this.scrollingMap.position);
                    // same thing with the angle
                    var angle = this.scrollingMap.savedPosition.angle(this.scrollingMap.position);
                    // if the distance is at least 4 pixels (an arbitrary value to see I am swiping)
                    if(distance > 4){
                         // set moving speed value
                         this.scrollingMap.movingSpeed = distance * speedMult;
                         // set moving angle value
                         this.scrollingMap.movingangle = angle;
                    }
               }
          }
     }
}