/*
p5.play
by Paolo Pedercini/molleindustria, 2015
http://molleindustria.org/
*/

(function (root, factory) {
  if (typeof define === 'function' && define.amd)
    define('p5.play', ['p5'], function (p5) { (factory(p5)); });
  else if (typeof exports === 'object')
    factory(require('../p5'));
  else
    factory(root.p5);
}(this, function (p5) {
  /**
   * p5.play is a library for p5.js to facilitate the creation of games and gamelike
   * projects.
   *
   * It provides a flexible Sprite class to manage visual objects in 2D space
   * and features such as animation support, basic collision detection
   * and resolution, mouse and keyboard interactions, and a virtual camera.
   *
   * p5.play is not a box2D-derived physics engine, it doesn't use events, and it's
   * designed to be understood and possibly modified by intermediate programmers.
   *
   * See the examples folder for more info on how to use this library.
   *
   * @module p5.play
   * @submodule p5.play
   * @for p5.play
   * @main
   */

  // =============================================================================
  //                         initialization
  // =============================================================================

  // This is the new way to initialize custom p5 properties for any p5 instance.
  // The goal is to migrate lazy P5 properties over to this method.
  // @see https://github.com/molleindustria/p5.play/issues/46
  p5.prototype.registerMethod('init', function p5PlayInit() {
    /**
     * The sketch camera automatically created at the beginning of a sketch.
     * A camera facilitates scrolling and zooming for scenes extending beyond
     * the canvas. A camera has a position, a zoom factor, and the mouse
     * coordinates relative to the view.
     *
     * In p5.js terms the camera wraps the whole drawing cycle in a
     * transformation matrix but it can be disabled anytime during the draw
     * cycle, for example to draw interface elements in an absolute position.
     *
     * @property camera
     * @type {camera}
     */
    this.camera = new Camera(this, 0, 0, 1);
    this.camera.init = false;
  });

  // This provides a way for us to lazily define properties that
  // are global to p5 instances.
  //
  // Note that this isn't just an optimization: p5 currently provides no
  // way for add-ons to be notified when new p5 instances are created, so
  // lazily creating these properties is the *only* mechanism available
  // to us. For more information, see:
  //
  // https://github.com/processing/p5.js/issues/1263
  function defineLazyP5Property(name, getter) {
    Object.defineProperty(p5.prototype, name, {
      configurable: true,
      enumerable: true,
      get: function () {
        var context = (this instanceof p5 && !this._isGlobal) ? this : window;

        if (typeof (context._p5PlayProperties) === 'undefined') {
          context._p5PlayProperties = {};
        }
        if (!(name in context._p5PlayProperties)) {
          context._p5PlayProperties[name] = getter.call(context);
        }
        return context._p5PlayProperties[name];
      }
    });
  }

  // This returns a factory function, suitable for passing to
  // defineLazyP5Property, that returns a subclass of the given
  // constructor that is always bound to a particular p5 instance.
  function boundConstructorFactory(constructor) {
    if (typeof (constructor) !== 'function')
      throw new Error('constructor must be a function');

    return function createBoundConstructor() {
      var pInst = this;

      function F() {
        var args = Array.prototype.slice.call(arguments);

        return constructor.apply(this, [pInst].concat(args));
      }
      F.prototype = constructor.prototype;

      return F;
    };
  }

  // This is a utility that makes it easy to define convenient aliases to
  // pre-bound p5 instance methods.
  //
  // For example:
  //
  //   var pInstBind = createPInstBinder(pInst);
  //
  //   var createVector = pInstBind('createVector');
  //   var loadImage = pInstBind('loadImage');
  //
  // The above will create functions createVector and loadImage, which can be
  // used similar to p5 global mode--however, they're bound to specific p5
  // instances, and can thus be used outside of global mode.
  function createPInstBinder(pInst) {
    return function pInstBind(methodName) {
      var method = pInst[methodName];

      if (typeof (method) !== 'function')
        throw new Error('"' + methodName + '" is not a p5 method');
      return method.bind(pInst);
    };
  }

  // These are utility p5 functions that don't depend on p5 instance state in
  // order to work properly, so we'll go ahead and make them easy to
  // access without needing to bind them to a p5 instance.
  var abs = p5.prototype.abs;
  var radians = p5.prototype.radians;
  var dist = p5.prototype.dist;
  var degrees = p5.prototype.degrees;
  var pow = p5.prototype.pow;
  var round = p5.prototype.round;


  // =============================================================================
  //                         p5 additions
  // =============================================================================

  /**
  * A Group containing all the sprites in the sketch.
  *
  * @property allSprites
  * @type {Group}
  */

  defineLazyP5Property('allSprites', function () {
    return new p5.prototype.Group();
  });

  p5.prototype.spriteUpdate = true;

  /**
     * A Sprite is the main building block of p5.play:
     * an element able to store images or animations with a set of
     * properties such as position and visibility.
     * A Sprite can have a collider that defines the active area to detect
     * collisions or overlappings with other sprites and mouse interactions.
     *
     * Sprites created using createSprite (the preferred way) are added to the
     * allSprites group and given a depth value that puts it in front of all
     * other sprites.
     *
     * @method createSprite
     * @param {Number} x Initial x coordinate
     * @param {Number} y Initial y coordinate
     * @param {Number} width Width of the placeholder rectangle and of the
     *                       collider until an image or new collider are set
     * @param {Number} height Height of the placeholder rectangle and of the
     *                       collider until an image or new collider are set
     * @return {Object} The new sprite instance
     */

  p5.prototype.createSprite = function (x, y, width, height) {
    var s = new Sprite(this, x, y, width, height);
    s.depth = this.allSprites.maxDepth() + 1;
    this.allSprites.add(s);
    return s;
  };


  /**
     * Removes a Sprite from the sketch.
     * The removed Sprite won't be drawn or updated anymore.
     * Equivalent to Sprite.remove()
     *
     * @method removeSprite
     * @param {Object} sprite Sprite to be removed
  */
  p5.prototype.removeSprite = function (sprite) {
    sprite.remove();
  };

  /**
  * Updates all the sprites in the sketch (position, animation...)
  * it's called automatically at every draw().
  * It can be paused by passing a parameter true or false;
  * Note: it does not render the sprites.
  *
  * @method updateSprites
  * @param {Boolean} updating false to pause the update, true to resume
  */
  p5.prototype.updateSprites = function (upd) {

    if (upd === false)
      this.spriteUpdate = false;
    if (upd === true)
      this.spriteUpdate = true;

    if (this.spriteUpdate)
      for (var i = 0; i < this.allSprites.size(); i++) {
        this.allSprites.get(i).update();
      }
  };

  /**
  * Returns all the sprites in the sketch as an array
  *
  * @method getSprites
  * @return {Array} Array of Sprites
  */
  p5.prototype.getSprites = function () {

    //draw everything
    if (arguments.length === 0) {
      return this.allSprites.toArray();
    }
    else {
      var arr = [];
      //for every tag
      for (var j = 0; j < arguments.length; j++) {
        for (var i = 0; i < this.allSprites.size(); i++) {
          if (this.allSprites.get(i).isTagged(arguments[j]))
            arr.push(this.allSprites.get(i));
        }
      }

      return arr;
    }

  };

  /**
  * Displays a Group of sprites.
  * If no parameter is specified, draws all sprites in the
  * sketch.
  * The drawing order is determined by the Sprite property "depth"
  *
  * @method drawSprites
  * @param {Group} [group] Group of Sprites to be displayed
  */
  p5.prototype.drawSprites = function (group) {
    // If no group is provided, draw the allSprites group.
    group = group || this.allSprites;

    if (typeof group.draw !== 'function') {
      throw ('Error: with drawSprites you can only draw all sprites or a group');
    }

    group.draw();
  };

  /**
  * Displays a Sprite.
  * To be typically used in the main draw function.
  *
  * @method drawSprite
  * @param {Sprite} sprite Sprite to be displayed
  */
  p5.prototype.drawSprite = function (sprite) {
    if (sprite)
      sprite.display();
  };

  /**
  * Loads an animation.
  * To be typically used in the preload() function of the sketch.
  *
  * @method loadAnimation
  * @param {Sprite} sprite Sprite to be displayed
  */
  p5.prototype.loadAnimation = function () {
    return construct(this.Animation, arguments);
  };

  /**
   * Loads a Sprite Sheet.
   * To be typically used in the preload() function of the sketch.
   *
   * @method loadSpriteSheet
   */
  p5.prototype.loadSpriteSheet = function () {
    return construct(this.SpriteSheet, arguments);
  };

  /**
  * Displays an animation.
  *
  * @method animation
  * @param {Animation} anim Animation to be displayed
  * @param {Number} x X coordinate
  * @param {Number} y Y coordinate
  *
  */
  p5.prototype.animation = function (anim, x, y) {
    anim.draw(x, y);
  };

  //variable to detect instant presses
  defineLazyP5Property('_p5play', function () {
    return {
      keyStates: {},
      mouseStates: {}
    };
  });

  var KEY_IS_UP = 0;
  var KEY_WENT_DOWN = 1;
  var KEY_IS_DOWN = 2;
  var KEY_WENT_UP = 3;

  /**
  * Detects if a key was pressed during the last cycle.
  * It can be used to trigger events once, when a key is pressed or released.
  * Example: Super Mario jumping.
  *
  * @method keyWentDown
  * @param {Number|String} key Key code or character
  * @return {Boolean} True if the key was pressed
  */
  p5.prototype.keyWentDown = function (key) {
    return this._isKeyInState(key, KEY_WENT_DOWN);
  };


  /**
  * Detects if a key was released during the last cycle.
  * It can be used to trigger events once, when a key is pressed or released.
  * Example: Spaceship shooting.
  *
  * @method keyWentUp
  * @param {Number|String} key Key code or character
  * @return {Boolean} True if the key was released
  */
  p5.prototype.keyWentUp = function (key) {
    return this._isKeyInState(key, KEY_WENT_UP);
  };

  /**
  * Detects if a key is currently pressed
  * Like p5 keyIsDown but accepts strings and codes
  *
  * @method keyDown
  * @param {Number|String} key Key code or character
  * @return {Boolean} True if the key is down
  */
  p5.prototype.keyDown = function (key) {
    return this._isKeyInState(key, KEY_IS_DOWN);
  };

  /**
   * Detects if a key is in the given state during the last cycle.
   * Helper method encapsulating common key state logic; it may be preferable
   * to call keyDown or other methods directly.
   *
   * @private
   * @method _isKeyInState
   * @param {Number|String} key Key code or character
   * @param {Number} state Key state to check against
   * @return {Boolean} True if the key is in the given state
   */
  p5.prototype._isKeyInState = function (key, state) {
    var keyCode;
    var keyStates = this._p5play.keyStates;

    if (typeof key === 'string') {
      keyCode = this._keyCodeFromAlias(key);
    }
    else {
      keyCode = key;
    }

    //if undefined start checking it
    if (keyStates[keyCode] === undefined) {
      if (this.keyIsDown(keyCode))
        keyStates[keyCode] = KEY_IS_DOWN;
      else
        keyStates[keyCode] = KEY_IS_UP;
    }

    return (keyStates[keyCode] === state);
  };

  /**
  * Detects if a mouse button is currently down
  * Combines mouseIsPressed and mouseButton of p5
  *
  * @method mouseDown
  * @param {Number} [buttonCode] Mouse button constant LEFT, RIGHT or CENTER
  * @return {Boolean} True if the button is down
  */
  p5.prototype.mouseDown = function (buttonCode) {
    return this._isMouseButtonInState(buttonCode, KEY_IS_DOWN);
  };

  /**
  * Detects if a mouse button is currently up
  * Combines mouseIsPressed and mouseButton of p5
  *
  * @method mouseUp
  * @param {Number} [buttonCode] Mouse button constant LEFT, RIGHT or CENTER
  * @return {Boolean} True if the button is up
  */
  p5.prototype.mouseUp = function (buttonCode) {
    return this._isMouseButtonInState(buttonCode, KEY_IS_UP);
  };

  /**
   * Detects if a mouse button was released during the last cycle.
   * It can be used to trigger events once, to be checked in the draw cycle
   *
   * @method mouseWentUp
   * @param {Number} [buttonCode] Mouse button constant LEFT, RIGHT or CENTER
   * @return {Boolean} True if the button was just released
   */
  p5.prototype.mouseWentUp = function (buttonCode) {
    return this._isMouseButtonInState(buttonCode, KEY_WENT_UP);
  };


  /**
   * Detects if a mouse button was pressed during the last cycle.
   * It can be used to trigger events once, to be checked in the draw cycle
   *
   * @method mouseWentDown
   * @param {Number} [buttonCode] Mouse button constant LEFT, RIGHT or CENTER
   * @return {Boolean} True if the button was just pressed
   */
  p5.prototype.mouseWentDown = function (buttonCode) {
    return this._isMouseButtonInState(buttonCode, KEY_WENT_DOWN);
  };

  /**
   * Detects if a mouse button is in the given state during the last cycle.
   * Helper method encapsulating common mouse button state logic; it may be
   * preferable to call mouseWentUp, etc, directly.
   *
   * @private
   * @method _isMouseButtonInState
   * @param {Number} [buttonCode] Mouse button constant LEFT, RIGHT or CENTER
   * @param {Number} state
   * @return {boolean} True if the button was in the given state
   */
  p5.prototype._isMouseButtonInState = function (buttonCode, state) {
    var mouseStates = this._p5play.mouseStates;

    if (buttonCode === undefined)
      buttonCode = this.LEFT;

    //undefined = not tracked yet, start tracking
    if (mouseStates[buttonCode] === undefined) {
      if (this.mouseIsPressed && this.mouseButton === buttonCode)
        mouseStates[buttonCode] = KEY_IS_DOWN;
      else
        mouseStates[buttonCode] = KEY_IS_UP;
    }

    return (mouseStates[buttonCode] === state);
  };


  /**
   * An object storing all useful keys for easy access
   * Key.tab = 9
   *
   * @private
   * @property KEY
   * @type {Object}
   */
  p5.prototype.KEY = {
    'BACKSPACE': 8,
    'TAB': 9,
    'ENTER': 13,
    'SHIFT': 16,
    'CTRL': 17,
    'ALT': 18,
    'PAUSE': 19,
    'CAPS_LOCK': 20,
    'ESC': 27,
    'SPACE': 32,
    ' ': 32,
    'PAGE_UP': 33,
    'PAGE_DOWN': 34,
    'END': 35,
    'HOME': 36,
    'LEFT_ARROW': 37,
    'LEFT': 37,
    'UP_ARROW': 38,
    'UP': 38,
    'RIGHT_ARROW': 39,
    'RIGHT': 39,
    'DOWN_ARROW': 40,
    'DOWN': 40,
    'INSERT': 45,
    'DELETE': 46,
    '0': 48,
    '1': 49,
    '2': 50,
    '3': 51,
    '4': 52,
    '5': 53,
    '6': 54,
    '7': 55,
    '8': 56,
    '9': 57,
    'A': 65,
    'B': 66,
    'C': 67,
    'D': 68,
    'E': 69,
    'F': 70,
    'G': 71,
    'H': 72,
    'I': 73,
    'J': 74,
    'K': 75,
    'L': 76,
    'M': 77,
    'N': 78,
    'O': 79,
    'P': 80,
    'Q': 81,
    'R': 82,
    'S': 83,
    'T': 84,
    'U': 85,
    'V': 86,
    'W': 87,
    'X': 88,
    'Y': 89,
    'Z': 90,
    '0NUMPAD': 96,
    '1NUMPAD': 97,
    '2NUMPAD': 98,
    '3NUMPAD': 99,
    '4NUMPAD': 100,
    '5NUMPAD': 101,
    '6NUMPAD': 102,
    '7NUMPAD': 103,
    '8NUMPAD': 104,
    '9NUMPAD': 105,
    'MULTIPLY': 106,
    'PLUS': 107,
    'MINUS': 109,
    'DOT': 110,
    'SLASH1': 111,
    'F1': 112,
    'F2': 113,
    'F3': 114,
    'F4': 115,
    'F5': 116,
    'F6': 117,
    'F7': 118,
    'F8': 119,
    'F9': 120,
    'F10': 121,
    'F11': 122,
    'F12': 123,
    'EQUAL': 187,
    'COMMA': 188,
    'SLASH': 191,
    'BACKSLASH': 220
  };

  /**
   * An object storing deprecated key aliases, which we still support but
   * should be mapped to valid aliases and generate warnings.
   *
   * @private
   * @property KEY_DEPRECATIONS
   * @type {Object}
   */
  p5.prototype.KEY_DEPRECATIONS = {
    'MINUT': 'MINUS',
    'COMA': 'COMMA'
  };

  /**
   * Given a string key alias (as defined in the KEY property above), look up
   * and return the numeric JavaScript key code for that key.  If a deprecated
   * alias is passed (as defined in the KEY_DEPRECATIONS property) it will be
   * mapped to a valid key code, but will also generate a warning about use
   * of the deprecated alias.
   *
   * @private
   * @method _keyCodeFromAlias
   * @param {!string} alias - a case-insensitive key alias
   * @return {number|undefined} a numeric JavaScript key code, or undefined
   *          if no key code matching the given alias is found.
   */
  p5.prototype._keyCodeFromAlias = function (alias) {
    alias = alias.toUpperCase();
    if (this.KEY_DEPRECATIONS[alias]) {
      this._warn('Key literal "' + alias + '" is deprecated and may be removed ' +
        'in a future version of p5.play. ' +
        'Please use "' + this.KEY_DEPRECATIONS[alias] + '" instead.');
      alias = this.KEY_DEPRECATIONS[alias];
    }
    return this.KEY[alias];
  };

  //pre draw: detect keyStates
  p5.prototype.readPresses = function () {
    var keyStates = this._p5play.keyStates;
    var mouseStates = this._p5play.mouseStates;

    for (var key in keyStates) {
      if (this.keyIsDown(key)) //if is down
      {
        if (keyStates[key] === KEY_IS_UP)//and was up
          keyStates[key] = KEY_WENT_DOWN;
        else
          keyStates[key] = KEY_IS_DOWN; //now is simply down
      }
      else //if it's up
      {
        if (keyStates[key] === KEY_IS_DOWN)//and was up
          keyStates[key] = KEY_WENT_UP;
        else
          keyStates[key] = KEY_IS_UP; //now is simply down
      }
    }

    //mouse
    for (var btn in mouseStates) {

      if (this.mouseIsPressed && this.mouseButton === btn) //if is down
      {
        if (mouseStates[btn] === KEY_IS_UP)//and was up
          mouseStates[btn] = KEY_WENT_DOWN;
        else
          mouseStates[btn] = KEY_IS_DOWN; //now is simply down
      }
      else //if it's up
      {
        if (mouseStates[btn] === KEY_IS_DOWN)//and was up
          mouseStates[btn] = KEY_WENT_UP;
        else
          mouseStates[btn] = KEY_IS_UP; //now is simply down
      }
    }

  };

  /**
  * Turns the quadTree on or off.
  * A quadtree is a data structure used to optimize collision detection.
  * It can improve performance when there is a large number of Sprites to be
  * checked continuously for overlapping.
  *
  * p5.play will create and update a quadtree automatically.
  *
  * @method useQuadTree
  * @param {Boolean} use Pass true to enable, false to disable
  */
  p5.prototype.useQuadTree = function (use) {

    if (this.quadTree !== undefined) {
      if (use === undefined)
        return this.quadTree.active;
      else if (use)
        this.quadTree.active = true;
      else
        this.quadTree.active = false;
    }
    else
      return false;
  };

  //the actual quadTree
  defineLazyP5Property('quadTree', function () {
    return new Quadtree({
      x: 0,
      y: 0,
      width: 0,
      height: 0
    }, 4);
  });

  /*
  //framerate independent delta, doesn't really work
  p5.prototype.deltaTime = 1;
  
  var now = Date.now();
  var then = Date.now();
  var INTERVAL_60 = 0.0166666; //60 fps
  
  function updateDelta() {
  then = now;
  now = Date.now();
  deltaTime = ((now - then) / 1000)/INTERVAL_60; // seconds since last frame
  }
  */

  /**
     * A Sprite is the main building block of p5.play:
     * an element able to store images or animations with a set of
     * properties such as position and visibility.
     * A Sprite can have a collider that defines the active area to detect
     * collisions or overlappings with other sprites and mouse interactions.
     *
     * To create a Sprite, use
     * {{#crossLink "p5.play/createSprite:method"}}{{/crossLink}}.
     *
     * @class Sprite
     */

  // For details on why these docs aren't in a YUIDoc comment block, see:
  //
  // https://github.com/molleindustria/p5.play/pull/67
  //
  // @param {Number} x Initial x coordinate
  // @param {Number} y Initial y coordinate
  // @param {Number} width Width of the placeholder rectangle and of the
  //                       collider until an image or new collider are set
  // @param {Number} height Height of the placeholder rectangle and of the
  //                        collider until an image or new collider are set
  function Sprite(pInst, _x, _y, _w, _h) {
    var pInstBind = createPInstBinder(pInst);

    var createVector = pInstBind('createVector');
    var color = pInstBind('color');
    var random = pInstBind('random');
    var print = pInstBind('print');
    var push = pInstBind('push');
    var pop = pInstBind('pop');
    var colorMode = pInstBind('colorMode');
    var noStroke = pInstBind('noStroke');
    var rectMode = pInstBind('rectMode');
    var ellipseMode = pInstBind('ellipseMode');
    var imageMode = pInstBind('imageMode');
    var translate = pInstBind('translate');
    var scale = pInstBind('scale');
    var rotate = pInstBind('rotate');
    var stroke = pInstBind('stroke');
    var strokeWeight = pInstBind('strokeWeight');
    var line = pInstBind('line');
    var noFill = pInstBind('noFill');
    var fill = pInstBind('fill');
    var textAlign = pInstBind('textAlign');
    var textSize = pInstBind('textSize');
    var text = pInstBind('text');
    var rect = pInstBind('rect');
    var cos = pInstBind('cos');
    var sin = pInstBind('sin');
    var atan2 = pInstBind('atan2');

    var quadTree = pInst.quadTree;
    var camera = pInst.camera;


    // These are p5 constants that we'd like easy access to.
    var RGB = p5.prototype.RGB;
    var CENTER = p5.prototype.CENTER;
    var LEFT = p5.prototype.LEFT;
    var BOTTOM = p5.prototype.BOTTOM;

    /**
    * The sprite's position of the sprite as a vector (x,y).
    * @property position
    * @type {p5.Vector}
    */
    this.position = createVector(_x, _y);

    /**
    * The sprite's position at the beginning of the last update as a vector (x,y).
    * @property previousPosition
    * @type {p5.Vector}
    */
    this.previousPosition = createVector(_x, _y);

    /*
    The sprite's position at the end of the last update as a vector (x,y).
    Note: this will differ from position whenever the position is changed
    directly by assignment.
    */
    this.newPosition = createVector(_x, _y);

    //Position displacement on the x coordinate since the last update
    this.deltaX = 0;
    this.deltaY = 0;

    /**
    * The sprite's velocity as a vector (x,y)
    * Velocity is speed broken down to its vertical and horizontal components.
    *
    * @property velocity
    * @type {p5.Vector}
    */
    this.velocity = createVector(0, 0);

    /**
    * Set a limit to the sprite's scalar speed regardless of the direction.
    * The value can only be positive. If set to -1, there's no limit.
    *
    * @property maxSpeed
    * @type {Number}
    * @default -1
    */
    this.maxSpeed = -1;

    /**
    * Friction factor, reduces the sprite's velocity.
    * The friction should be close to 0 (eg. 0.01)
    * 0: no friction
    * 1: full friction
    *
    * @property friction
    * @type {Number}
    * @default 0
    */
    this.friction = 0;

    /**
    * The sprite's current collider.
    * It can either be an Axis Aligned Bounding Box (a non-rotated rectangle)
    * or a circular collider.
    * If the sprite is checked for collision, bounce, overlapping or mouse events the
    * collider is automatically created from the width and height
    * of the sprite or from the image dimension in case of animate sprites
    *
    * You can set a custom collider with Sprite.setCollider
    *
    * @property collider
    * @type {Object}
    */
    this.collider = undefined;

    //internal use
    //"default" - no image or custom collider is specified, use the shape width / height
    //"custom" - specified with setCollider
    //"image" - no collider is set with setCollider and an image is added
    this.colliderType = 'none';

    /**
    * Object containing information about the most recent collision/overlapping
    * To be typically used in combination with Sprite.overlap or Sprite.collide
    * functions.
    * The properties are touching.left, touching.right, touching.top,
    * touching.bottom and are either true or false depending on the side of the
    * collider.
    *
    * @property touching
    * @type {Object}
    */
    this.touching = {};
    this.touching.left = false;
    this.touching.right = false;
    this.touching.top = false;
    this.touching.bottom = false;

    /**
    * The mass determines the velocity transfer when sprites bounce
    * against each other. See Sprite.bounce
    * The higher the mass the least the sprite will be affected by collisions.
    *
    * @property mass
    * @type {Number}
    * @default 1
    */
    this.mass = 1;

    /**
    * If set to true the sprite won't bounce or be displaced by collisions
    * Simulates an infinite mass or an anchored object.
    *
    * @property immovable
    * @type {Boolean}
    * @default false
    */
    this.immovable = false;

    //Coefficient of restitution - velocity lost in the bouncing
    //0 perfectly inelastic , 1 elastic, > 1 hyper elastic

    /**
    * Coefficient of restitution. The velocity lost after bouncing.
    * 1: perfectly elastic, no energy is lost
    * 0: perfectly inelastic, no bouncing
    * less than 1: inelastic, this is the most common in nature
    * greater than 1: hyper elastic, energy is increased like in a pinball bumper
    *
    * @property restitution
    * @type {Number}
    * @default 1
    */
    this.restitution = 1;

    /**
    * Rotation in degrees of the visual element (image or animation)
    * Note: this is not the movement's direction, see getDirection.
    *
    * @property rotation
    * @type {Number}
    * @default 0
    */
    Object.defineProperty(this, 'rotation', {
      enumerable: true,
      get: function () {
        return this._rotation;
      },
      set: function (value) {
        this._rotation = value;
        if (this.rotateToDirection) {
          this.setSpeed(this.getSpeed(), value);
        }
      }
    });

    /**
    * Internal rotation variable (expressed in degrees).
    * Note: external callers access this through the rotation property above.
    *
    * @private
    * @property _rotation
    * @type {Number}
    * @default 0
    */
    this._rotation = 0;

    /**
    * Rotation change in degrees per frame of thevisual element (image or animation)
    * Note: this is not the movement's direction, see getDirection.
    *
    * @property rotationSpeed
    * @type {Number}
    * @default 0
    */
    this.rotationSpeed = 0;


    /**
    * Automatically lock the rotation property of the visual element
    * (image or animation) to the sprite's movement direction and vice versa.
    *
    * @property rotateToDirection
    * @type {Boolean}
    * @default false
    */
    this.rotateToDirection = false;


    /**
    * Determines the rendering order within a group: a sprite with
    * lower depth will appear below the ones with higher depth.
    *
    * Note: drawing a group before another with drawSprites will make
    * its members appear below the second one, like in normal p5 canvas
    * drawing.
    *
    * @property depth
    * @type {Number}
    * @default One more than the greatest existing sprite depth, when calling
    *          createSprite().  When calling new Sprite() directly, depth will
    *          initialize to 0 (not recommended).
    */
    this.depth = 0;

    /**
    * Determines the sprite's scale.
    * Example: 2 will be twice the native size of the visuals,
    * 0.5 will be half. Scaling up may make images blurry.
    *
    * @property scale
    * @type {Number}
    * @default 1
    */
    this.scale = 1;

    var dirX = 1;
    var dirY = 1;

    /**
    * The sprite's visibility.
    *
    * @property visible
    * @type {Boolean}
    * @default true
    */
    this.visible = true;

    /**
    * If set to true sprite will track its mouse state.
    * the properties mouseIsPressed and mouseIsOver will be updated.
    * Note: automatically set to true if the functions
    * onMouseReleased or onMousePressed are set.
    *
    * @property mouseActive
    * @type {Boolean}
    * @default false
    */
    this.mouseActive = false;

    /**
    * True if mouse is on the sprite's collider.
    * Read only.
    *
    * @property mouseIsOver
    * @type {Boolean}
    */
    this.mouseIsOver = false;

    /**
    * True if mouse is pressed on the sprite's collider.
    * Read only.
    *
    * @property mouseIsPressed
    * @type {Boolean}
    */
    this.mouseIsPressed = false;

    /*
    * Width of the sprite's current image.
    * If no images or animations are set it's the width of the
    * placeholder rectangle.
    * Used internally to make calculations and draw the sprite.
    *
    * @private
    * @property _internalWidth
    * @type {Number}
    * @default 100
    */
    this._internalWidth = _w;

    /*
    * Height of the sprite's current image.
    * If no images or animations are set it's the height of the
    * placeholder rectangle.
    * Used internally to make calculations and draw the sprite.
    *
    * @private
    * @property _internalHeight
    * @type {Number}
    * @default 100
    */
    this._internalHeight = _h;

    /*
     * _internalWidth and _internalHeight are used for all p5.play
     * calculations, but width and height can be extended. For example,
     * you may want users to always get and set a scaled width:
        Object.defineProperty(this, 'width', {
          enumerable: true,
          configurable: true,
          get: function() {
            return this._internalWidth * this.scale;
          },
          set: function(value) {
            this._internalWidth = value / this.scale;
          }
        });
     */

    /**
    * Width of the sprite's current image.
    * If no images or animations are set it's the width of the
    * placeholder rectangle.
    *
    * @property width
    * @type {Number}
    * @default 100
    */
    Object.defineProperty(this, 'width', {
      enumerable: true,
      configurable: true,
      get: function () {
        return this._internalWidth;
      },
      set: function (value) {
        this._internalWidth = value;
      }
    });

    if (_w === undefined)
      this.width = 100;
    else
      this.width = _w;

    /**
    * Height of the sprite's current image.
    * If no images or animations are set it's the height of the
    * placeholder rectangle.
    *
    * @property height
    * @type {Number}
    * @default 100
    */
    Object.defineProperty(this, 'height', {
      enumerable: true,
      configurable: true,
      get: function () {
        return this._internalHeight;
      },
      set: function (value) {
        this._internalHeight = value;
      }
    });

    if (_h === undefined)
      this.height = 100;
    else
      this.height = _h;

    /**
    * Unscaled width of the sprite
    * If no images or animations are set it's the width of the
    * placeholder rectangle.
    *
    * @property originalWidth
    * @type {Number}
    * @default 100
    */
    this.originalWidth = this._internalWidth;

    /**
    * Unscaled height of the sprite
    * If no images or animations are set it's the height of the
    * placeholder rectangle.
    *
    * @property originalHeight
    * @type {Number}
    * @default 100
    */
    this.originalHeight = this._internalHeight;

    /**
    * True if the sprite has been removed.
    *
    * @property removed
    * @type {Boolean}
    */
    this.removed = false;

    /**
    * Cycles before self removal.
    * Set it to initiate a countdown, every draw cycle the property is
    * reduced by 1 unit. At 0 it will call a sprite.remove()
    * Disabled if set to -1.
    *
    * @property life
    * @type {Number}
    * @default -1
    */
    this.life = -1;

    /**
    * If set to true, draws an outline of the collider, the depth, and center.
    *
    * @property debug
    * @type {Boolean}
    * @default false
    */
    this.debug = false;

    /**
    * If no image or animations are set this is color of the
    * placeholder rectangle
    *
    * @property shapeColor
    * @type {color}
    */
    this.shapeColor = color(random(255), random(255), random(255));

    /**
    * Groups the sprite belongs to, including allSprites
    *
    * @property groups
    * @type {Array}
    */
    this.groups = [];

    var animations = {};

    //The current animation's label.
    var currentAnimation = '';

    /**
    * Reference to the current animation.
    *
    * @property animation
    * @type {Animation}
    */
    this.animation = undefined;

    /*
     * @private
     * Keep animation properties in sync with how the animation changes.
     */
    this._syncAnimationSizes = function () {
      //has an animation but the collider is still default
      //the animation wasn't loaded. if the animation is not a 1x1 image
      //it means it just finished loading
      if (this.colliderType === 'default' &&
        animations[currentAnimation].getWidth() !== 1 && animations[currentAnimation].getHeight() !== 1) {
        this.collider = this.getBoundingBox();
        this.colliderType = 'image';
        this._internalWidth = animations[currentAnimation].getWidth() * abs(this._getScaleX());
        this._internalHeight = animations[currentAnimation].getHeight() * abs(this._getScaleY());
        //quadTree.insert(this);
      }

      //update size and collider
      if (animations[currentAnimation].frameChanged || this.width === undefined || this.height === undefined) {
        //this.collider = this.getBoundingBox();
        this._internalWidth = animations[currentAnimation].getWidth() * abs(this._getScaleX());
        this._internalHeight = animations[currentAnimation].getHeight() * abs(this._getScaleY());
      }
    };

    /**
    * Updates the sprite.
    * Called automatically at the beginning of the draw cycle.
    *
    * @method update
    */
    this.update = function () {

      if (!this.removed) {
        //if there has been a change somewhere after the last update
        //the old position is the last position registered in the update
        if (this.newPosition !== this.position)
          this.previousPosition = createVector(this.newPosition.x, this.newPosition.y);
        else
          this.previousPosition = createVector(this.position.x, this.position.y);

        this.velocity.x *= 1 - this.friction;
        this.velocity.y *= 1 - this.friction;

        if (this.maxSpeed !== -1)
          this.limitSpeed(this.maxSpeed);

        if (this.rotateToDirection && this.velocity.mag() > 0)
          this._rotation = this.getDirection();

        this.rotation += this.rotationSpeed;

        this.position.x += this.velocity.x;
        this.position.y += this.velocity.y;

        this.newPosition = createVector(this.position.x, this.position.y);

        this.deltaX = this.position.x - this.previousPosition.x;
        this.deltaY = this.position.y - this.previousPosition.y;

        //if there is an animation
        if (animations[currentAnimation]) {
          //update it
          animations[currentAnimation].update();

          this._syncAnimationSizes();
        }

        //a collider is created either manually with setCollider or
        //when I check this sprite for collisions or overlaps
        if (this.collider) {
          if (this.collider instanceof AABB) {
            //scale / rotate collider
            var t;
            if (pInst._angleMode === pInst.RADIANS) {
              t = radians(this.rotation);
            } else {
              t = this.rotation;
            }

            if (this.colliderType === 'custom') {
              this.collider.extents.x = this.collider.originalExtents.x * abs(this._getScaleX()) * abs(cos(t)) +
                this.collider.originalExtents.y * abs(this._getScaleY()) * abs(sin(t));

              this.collider.extents.y = this.collider.originalExtents.x * abs(this._getScaleX()) * abs(sin(t)) +
                this.collider.originalExtents.y * abs(this._getScaleY()) * abs(cos(t));
            }
            else if (this.colliderType === 'default') {
              this.collider.extents.x = this._internalWidth * abs(this._getScaleX()) * abs(cos(t)) +
                this._internalHeight * abs(this._getScaleY()) * abs(sin(t));
              this.collider.extents.y = this._internalWidth * abs(this._getScaleX()) * abs(sin(t)) +
                this._internalHeight * abs(this._getScaleY()) * abs(cos(t));
            }
            else if (this.colliderType === 'image') {
              this.collider.extents.x = this._internalWidth * abs(cos(t)) +
                this._internalHeight * abs(sin(t));

              this.collider.extents.y = this._internalWidth * abs(sin(t)) +
                this._internalHeight * abs(cos(t));
            }
          }

          if (this.collider instanceof CircleCollider) {
            //print(this.scale);
            this.collider.radius = this.collider.originalRadius * abs(this.scale);
          }

        }//end collider != null

        //mouse actions
        if (this.mouseActive) {
          //if no collider set it
          if (!this.collider)
            this.setDefaultCollider();

          this.mouseUpdate();
        }
        else {
          if (typeof (this.onMouseOver) === 'function' ||
            typeof (this.onMouseOut) === 'function' ||
            typeof (this.onMousePressed) === 'function' ||
            typeof (this.onMouseReleased) === 'function') {
            //if a mouse function is set
            //it's implied we want to have it mouse active so
            //we do this automatically
            this.mouseActive = true;

            //if no collider set it
            if (!this.collider)
              this.setDefaultCollider();

            this.mouseUpdate();
          }
        }

        //self destruction countdown
        if (this.life > 0)
          this.life--;
        if (this.life === 0)
          this.remove();
      }
    };//end update

    /**
     * Creates a default collider matching the size of the
     * placeholder rectangle or the bounding box of the image.
     *
     * @method setDefaultCollider
     */
    this.setDefaultCollider = function () {

      //if has animation get the animation bounding box
      //working only for preloaded images
      if (animations[currentAnimation] && (animations[currentAnimation].getWidth() !== 1 && animations[currentAnimation].getHeight() !== 1)) {
        this.collider = this.getBoundingBox();
        this._internalWidth = animations[currentAnimation].getWidth() * abs(this._getScaleX());
        this._internalHeight = animations[currentAnimation].getHeight() * abs(this._getScaleY());
        //quadTree.insert(this);
        this.colliderType = 'image';
        //print("IMAGE COLLIDER ADDED");
      }
      else if (animations[currentAnimation] && animations[currentAnimation].getWidth() === 1 && animations[currentAnimation].getHeight() === 1) {
        //animation is still loading
        //print("wait");
      }
      else //get the with and height defined at the creation
      {
        this.collider = new AABB(pInst, this.position, createVector(this._internalWidth, this._internalHeight));
        //quadTree.insert(this);
        this.colliderType = 'default';
      }

      pInst.quadTree.insert(this);
    };

    /**
     * Updates the sprite mouse states and triggers the mouse events:
     * onMouseOver, onMouseOut, onMousePressed, onMouseReleased
     *
     * @method mouseUpdate
     */
    this.mouseUpdate = function () {

      var mouseWasOver = this.mouseIsOver;
      var mouseWasPressed = this.mouseIsPressed;

      this.mouseIsOver = false;
      this.mouseIsPressed = false;

      var mousePosition;

      if (camera.active)
        mousePosition = createVector(camera.mouseX, camera.mouseY);
      else
        mousePosition = createVector(pInst.mouseX, pInst.mouseY);

      //rollover
      if (this.collider) {

        if (this.collider instanceof CircleCollider) {
          if (dist(mousePosition.x, mousePosition.y, this.collider.center.x, this.collider.center.y) < this.collider.radius)
            this.mouseIsOver = true;
        } else if (this.collider instanceof AABB) {
          if (mousePosition.x > this.collider.left() &&
            mousePosition.y > this.collider.top() &&
            mousePosition.x < this.collider.right() &&
            mousePosition.y < this.collider.bottom()) {
            this.mouseIsOver = true;
          }
        }

        //global p5 var
        if (this.mouseIsOver && pInst.mouseIsPressed)
          this.mouseIsPressed = true;

        //event change - call functions
        if (!mouseWasOver && this.mouseIsOver && this.onMouseOver !== undefined)
          if (typeof (this.onMouseOver) === 'function')
            this.onMouseOver.call(this, this);
          else
            print('Warning: onMouseOver should be a function');

        if (mouseWasOver && !this.mouseIsOver && this.onMouseOut !== undefined)
          if (typeof (this.onMouseOut) === 'function')
            this.onMouseOut.call(this, this);
          else
            print('Warning: onMouseOut should be a function');

        if (!mouseWasPressed && this.mouseIsPressed && this.onMousePressed !== undefined)
          if (typeof (this.onMousePressed) === 'function')
            this.onMousePressed.call(this, this);
          else
            print('Warning: onMousePressed should be a function');

        if (mouseWasPressed && !pInst.mouseIsPressed && !this.mouseIsPressed && this.onMouseReleased !== undefined)
          if (typeof (this.onMouseReleased) === 'function')
            this.onMouseReleased.call(this, this);
          else
            print('Warning: onMouseReleased should be a function');

      }

    };

    /**
    * Sets a collider for the sprite.
    *
    * In p5.play a Collider is an invisible circle or rectangle
    * that can have any size or position relative to the sprite and which
    * will be used to detect collisions and overlapping with other sprites,
    * or the mouse cursor.
    *
    * If the sprite is checked for collision, bounce, overlapping or mouse events
    * a collider is automatically created from the width and height parameter
    * passed at the creation of the sprite or the from the image dimension in case
    * of animated sprites.
    *
    * Often the image bounding box is not appropriate as the active area for
    * collision detection so you can set a circular or rectangular sprite with
    * different dimensions and offset from the sprite's center.
    *
    * There are four ways to call this method:
    *
    * 1. setCollider("rectangle")
    * 2. setCollider("rectangle", offsetX, offsetY, width, height)
    * 3. setCollider("circle")
    * 4. setCollider("circle", offsetX, offsetY, radius)
    *
    * @method setCollider
    * @param {String} type Either "rectangle" or "circle"
    * @param {Number} offsetX Collider x position from the center of the sprite
    * @param {Number} offsetY Collider y position from the center of the sprite
    * @param {Number} width Collider width or radius
    * @param {Number} height Collider height
    * @throws {TypeError} if given invalid parameters.
    */
    this.setCollider = function (type, offsetX, offsetY, width, height) {
      if (!(type === 'rectangle' || type === 'circle')) {
        throw new TypeError('setCollider expects the first argument to be either "circle" or "rectangle"');
      } else if (type === 'circle' && arguments.length > 1 && arguments.length < 4) {
        throw new TypeError('Usage: setCollider("circle") or setCollider("circle", offsetX, offsetY, radius)');
      } else if (type === 'circle' && arguments.length > 4) {
        pInst._warn('Extra parameters to setCollider were ignored. Usage: setCollider("circle") or setCollider("circle", offsetX, offsetY, radius)');
      } else if (type === 'rectangle' && arguments.length > 1 && arguments.length < 5) {
        throw new TypeError('Usage: setCollider("rectangle") or setCollider("rectangle", offsetX, offsetY, width, height)');
      } else if (type === 'rectangle' && arguments.length > 5) {
        pInst._warn('Extra parameters to setCollider were ignored. Usage: setCollider("rectangle") or setCollider("rectangle", offsetX, offsetY, width, height)');
      }

      this.colliderType = 'custom';

      var v = createVector(offsetX, offsetY);
      if (type === 'rectangle' && arguments.length === 1) {
        this.collider = new AABB(pInst, this.position, createVector(this.width, this.height));
      } else if (type === 'rectangle' && arguments.length >= 5) {
        this.collider = new AABB(pInst, this.position, createVector(width, height), v);
      } else if (type === 'circle' && arguments.length === 1) {
        this.collider = new CircleCollider(pInst, this.position, Math.floor(Math.max(this.width, this.height) / 2));
      } else if (type === 'circle' && arguments.length >= 4) {
        this.collider = new CircleCollider(pInst, this.position, width, v);
      }

      quadTree.insert(this);
    };

    /**
     * Returns a the bounding box of the current image
     * @method getBoundingBox
     */
    this.getBoundingBox = function () {

      var w = animations[currentAnimation].getWidth() * abs(this._getScaleX());
      var h = animations[currentAnimation].getHeight() * abs(this._getScaleY());

      //if the bounding box is 1x1 the image is not loaded
      //potential issue with actual 1x1 images
      if (w === 1 && h === 1) {
        //not loaded yet
        return new AABB(pInst, this.position, createVector(w, h));
      }
      else {
        return new AABB(pInst, this.position, createVector(w, h));
      }
    };

    /**
    * Sets the sprite's horizontal mirroring.
    * If 1 the images displayed normally
    * If -1 the images are flipped horizontally
    * If no argument returns the current x mirroring
    *
    * @method mirrorX
    * @param {Number} dir Either 1 or -1
    * @return {Number} Current mirroring if no parameter is specified
    */
    this.mirrorX = function (dir) {
      if (dir === 1 || dir === -1)
        dirX = dir;
      else
        return dirX;
    };

    /**
    * Sets the sprite's vertical mirroring.
    * If 1 the images displayed normally
    * If -1 the images are flipped vertically
    * If no argument returns the current y mirroring
    *
    * @method mirrorY
    * @param {Number} dir Either 1 or -1
    * @return {Number} Current mirroring if no parameter is specified
    */
    this.mirrorY = function (dir) {
      if (dir === 1 || dir === -1)
        dirY = dir;
      else
        return dirY;
    };

    /*
     * Returns the value the sprite should be scaled in the X direction.
     * Used to calculate rendering and collisions.
     * @private
     */
    this._getScaleX = function () {
      return this.scale;
    };

    /*
     * Returns the value the sprite should be scaled in the Y direction.
     * Used to calculate rendering and collisions.
     * @private
     */
    this._getScaleY = function () {
      return this.scale;
    };

    /**
     * Manages the positioning, scale and rotation of the sprite
     * Called automatically, it should not be overridden
     * @private
     * @final
     * @method display
     */
    this.display = function () {
      if (this.visible && !this.removed) {
        push();
        colorMode(RGB);

        noStroke();
        rectMode(CENTER);
        ellipseMode(CENTER);
        imageMode(CENTER);

        translate(this.position.x, this.position.y);
        scale(this._getScaleX() * dirX, this._getScaleY() * dirY);
        if (pInst._angleMode === pInst.RADIANS) {
          rotate(radians(this.rotation));
        } else {
          rotate(this.rotation);
        }
        this.draw();
        //draw debug info
        pop();


        if (this.debug) {
          push();
          //draw the anchor point
          stroke(0, 255, 0);
          strokeWeight(1);
          line(this.position.x - 10, this.position.y, this.position.x + 10, this.position.y);
          line(this.position.x, this.position.y - 10, this.position.x, this.position.y + 10);
          noFill();

          //depth number
          noStroke();
          fill(0, 255, 0);
          textAlign(LEFT, BOTTOM);
          textSize(16);
          text(this.depth + '', this.position.x + 4, this.position.y - 2);

          noFill();
          stroke(0, 255, 0);

          //bounding box
          if (this.collider !== undefined) {
            this.collider.draw();
          }
          pop();
        }

      }
    };


    /**
    * Manages the visuals of the sprite.
    * It can be overridden with a custom drawing function.
    * The 0,0 point will be the center of the sprite.
    * Example:
    * sprite.draw = function() { ellipse(0,0,10,10) }
    * Will display the sprite as circle.
    *
    * @method draw
    */
    this.draw = function () {
      if (currentAnimation !== '' && animations) {
        if (animations[currentAnimation])
          animations[currentAnimation].draw(0, 0, 0);
      }
      else {
        noStroke();
        fill(this.shapeColor);
        rect(0, 0, this._internalWidth, this._internalHeight);
      }
    };

    /**
     * Removes the Sprite from the sketch.
     * The removed Sprite won't be drawn or updated anymore.
     *
     * @method remove
     */
    this.remove = function () {
      this.removed = true;

      quadTree.removeObject(this);

      //when removed from the "scene" also remove all the references in all the groups
      while (this.groups.length > 0) {
        this.groups[0].remove(this);
      }
    };

    /**
    * Sets the velocity vector.
    *
    * @method setVelocity
    * @param {Number} x X component
    * @param {Number} y Y component
    */
    this.setVelocity = function (x, y) {
      this.velocity.x = x;
      this.velocity.y = y;
    };

    /**
    * Calculates the scalar speed.
    *
    * @method getSpeed
    * @return {Number} Scalar speed
    */
    this.getSpeed = function () {
      return this.velocity.mag();
    };

    /**
    * Calculates the movement's direction in degrees.
    *
    * @method getDirection
    * @return {Number} Angle in degrees
    */
    this.getDirection = function () {

      var direction = atan2(this.velocity.y, this.velocity.x);

      if (isNaN(direction))
        direction = 0;

      // Unlike Math.atan2, the atan2 method above will return degrees if
      // the current p5 angleMode is DEGREES, and radians if the p5 angleMode is
      // RADIANS.  This method should always return degrees (for now).
      // See https://github.com/molleindustria/p5.play/issues/94
      if (pInst._angleMode === pInst.RADIANS) {
        direction = degrees(direction);
      }

      return direction;
    };

    /**
    * Adds the sprite to an existing group
    *
    * @method addToGroup
    * @param {Object} group
    */
    this.addToGroup = function (group) {
      if (group instanceof Array)
        group.add(this);
      else
        print('addToGroup error: ' + group + ' is not a group');
    };

    /**
    * Limits the scalar speed.
    *
    * @method limitSpeed
    * @param {Number} max Max speed: positive number
    */
    this.limitSpeed = function (max) {

      //update linear speed
      var speed = this.getSpeed();

      if (abs(speed) > max) {
        //find reduction factor
        var k = max / abs(speed);
        this.velocity.x *= k;
        this.velocity.y *= k;
      }
    };

    /**
    * Set the speed and direction of the sprite.
    * The action overwrites the current velocity.
    * If direction is not supplied, the current direction is maintained.
    * If direction is not supplied and there is no current velocity, the current
    * rotation angle used for the direction.
    *
    * @method setSpeed
    * @param {Number}  speed Scalar speed
    * @param {Number}  [angle] Direction in degrees
    */
    this.setSpeed = function (speed, angle) {
      var a;
      if (typeof angle === 'undefined') {
        if (this.velocity.x !== 0 || this.velocity.y !== 0) {
          a = pInst.atan2(this.velocity.y, this.velocity.x);
        } else {
          if (pInst._angleMode === pInst.RADIANS) {
            a = radians(this._rotation);
          } else {
            a = this._rotation;
          }
        }
      } else {
        if (pInst._angleMode === pInst.RADIANS) {
          a = radians(angle);
        } else {
          a = angle;
        }
      }
      this.velocity.x = cos(a) * speed;
      this.velocity.y = sin(a) * speed;
    };

    /**
    * Pushes the sprite in a direction defined by an angle.
    * The force is added to the current velocity.
    *
    * @method addSpeed
    * @param {Number}  speed Scalar speed to add
    * @param {Number}  angle Direction in degrees
    */
    this.addSpeed = function (speed, angle) {
      var a;
      if (pInst._angleMode === pInst.RADIANS) {
        a = radians(angle);
      } else {
        a = angle;
      }
      this.velocity.x += cos(a) * speed;
      this.velocity.y += sin(a) * speed;
    };

    /**
    * Pushes the sprite toward a point.
    * The force is added to the current velocity.
    *
    * @method attractionPoint
    * @param {Number}  magnitude Scalar speed to add
    * @param {Number}  pointX Direction x coordinate
    * @param {Number}  pointY Direction y coordinate
    */
    this.attractionPoint = function (magnitude, pointX, pointY) {
      var angle = atan2(pointY - this.position.y, pointX - this.position.x);
      this.velocity.x += cos(angle) * magnitude;
      this.velocity.y += sin(angle) * magnitude;
    };


    /**
    * Adds an image to the sprite.
    * An image will be considered a one-frame animation.
    * The image should be preloaded in the preload() function using p5 loadImage.
    * Animations require a identifying label (string) to change them.
    * The image is stored in the sprite but not necessarily displayed
    * until Sprite.changeAnimation(label) is called
    *
    * Usages:
    * - sprite.addImage(label, image);
    * - sprite.addImage(image);
    *
    * If only an image is passed no label is specified
    *
    * @method addImage
    * @param {String|p5.Image} label Label or image
    * @param {p5.Image} [img] Image
    */
    this.addImage = function () {
      if (typeof arguments[0] === 'string' && arguments[1] instanceof p5.Image)
        this.addAnimation(arguments[0], arguments[1]);
      else if (arguments[0] instanceof p5.Image)
        this.addAnimation('normal', arguments[0]);
      else
        throw ('addImage error: allowed usages are <image> or <label>, <image>');
    };

    /**
    * Adds an animation to the sprite.
    * The animation should be preloaded in the preload() function
    * using loadAnimation.
    * Animations require a identifying label (string) to change them.
    * Animations are stored in the sprite but not necessarily displayed
    * until Sprite.changeAnimation(label) is called.
    *
    * Usage:
    * - sprite.addAnimation(label, animation);
    *
    * Alternative usages. See Animation for more information on file sequences:
    * - sprite.addAnimation(label, firstFrame, lastFrame);
    * - sprite.addAnimation(label, frame1, frame2, frame3...);
    *
    * @method addAnimation
    * @param {String} label Animation identifier
    * @param {Animation} animation The preloaded animation
    */
    this.addAnimation = function (label) {
      var anim;

      if (typeof label !== 'string') {
        print('Sprite.addAnimation error: the first argument must be a label (String)');
        return -1;
      }
      else if (arguments.length < 2) {
        print('addAnimation error: you must specify a label and n frame images');
        return -1;
      }
      else if (arguments[1] instanceof Animation) {

        var sourceAnimation = arguments[1];

        var newAnimation = sourceAnimation.clone();

        animations[label] = newAnimation;

        if (currentAnimation === '') {
          currentAnimation = label;
          this.animation = newAnimation;
        }

        newAnimation.isSpriteAnimation = true;

        this._internalWidth = newAnimation.getWidth() * abs(this._getScaleX());
        this._internalHeight = newAnimation.getHeight() * abs(this._getScaleY());

        return newAnimation;
      }
      else {
        var animFrames = [];
        for (var i = 1; i < arguments.length; i++)
          animFrames.push(arguments[i]);

        anim = construct(pInst.Animation, animFrames);
        animations[label] = anim;

        if (currentAnimation === '') {
          currentAnimation = label;
          this.animation = anim;
        }
        anim.isSpriteAnimation = true;

        this._internalWidth = anim.getWidth() * abs(this._getScaleX());
        this._internalHeight = anim.getHeight() * abs(this._getScaleY());

        return anim;
      }

    };

    /**
    * Changes the displayed image/animation.
    * Equivalent to changeAnimation
    *
    * @method changeImage
    * @param {String} label Image/Animation identifier
    */
    this.changeImage = function (label) {
      this.changeAnimation(label);
    };

    /**
   * Returns the label of the current animation
   *
   * @method getAnimationLabel
   * @return {String} label Image/Animation identifier
   */
    this.getAnimationLabel = function () {
      return currentAnimation;
    };

    /**
    * Changes the displayed animation.
    * See Animation for more control over the sequence.
    *
    * @method changeAnimation
    * @param {String} label Animation identifier
    */
    this.changeAnimation = function (label) {
      if (!animations[label])
        print('changeAnimation error: no animation labeled ' + label);
      else {
        currentAnimation = label;
        this.animation = animations[label];
      }
    };

    /**
    * Checks if the given point corresponds to a transparent pixel
    * in the sprite's current image. It can be used to check a point collision
    * against only the visible part of the sprite.
    *
    * @method overlapPixel
    * @param {Number} pointX x coordinate of the point to check
    * @param {Number} pointY y coordinate of the point to check
    * @return {Boolean} result True if non-transparent
    */
    this.overlapPixel = function (pointX, pointY) {
      var point = createVector(pointX, pointY);

      var img = this.animation.getFrameImage();

      //convert point to img relative position
      point.x -= this.position.x - img.width / 2;
      point.y -= this.position.y - img.height / 2;

      //out of the image entirely
      if (point.x < 0 || point.x > img.width || point.y < 0 || point.y > img.height)
        return false;
      else if (this.rotation === 0 && this.scale === 1) {
        //true if full opacity
        var values = img.get(point.x, point.y);
        return values[3] === 255;
      }
      else {
        print('Error: overlapPixel doesn\'t work with scaled or rotated sprites yet');
        //offscreen printing to be implemented bleurch
        return false;
      }
    };

    /**
    * Checks if the given point is inside the sprite's collider.
    *
    * @method overlapPoint
    * @param {Number} pointX x coordinate of the point to check
    * @param {Number} pointY y coordinate of the point to check
    * @return {Boolean} result True if inside
    */
    this.overlapPoint = function (pointX, pointY) {
      var point = createVector(pointX, pointY);

      if (!this.collider)
        this.setDefaultCollider();

      if (this.collider !== undefined) {
        if (this.collider instanceof AABB)
          return (point.x > this.collider.left() && point.x < this.collider.right() && point.y > this.collider.top() && point.y < this.collider.bottom());
        if (this.collider instanceof CircleCollider) {
          var sqRadius = this.collider.radius * this.collider.radius;
          var sqDist = pow(this.collider.center.x - point.x, 2) + pow(this.collider.center.y - point.y, 2);
          return sqDist < sqRadius;
        }
        else
          return false;
      }
      else
        return false;

    };


    /**
    * Checks if the the sprite is overlapping another sprite or a group.
    * The check is performed using the colliders. If colliders are not set
    * they will be created automatically from the image/animation bounding box.
    *
    * A callback function can be specified to perform additional operations
    * when the overlap occours.
    * If the target is a group the function will be called for each single
    * sprite overlapping. The parameter of the function are respectively the
    * current sprite and the colliding sprite.
    *
    * @example
    *     sprite.overlap(otherSprite, explosion);
    *
    *     function explosion(spriteA, spriteB) {
    *       spriteA.remove();
    *       spriteB.score++;
    *     }
    *
    * @method overlap
    * @param {Object} target Sprite or group to check against the current one
    * @param {Function} [callback] The function to be called if overlap is positive
    * @return {Boolean} True if overlapping
    */
    this.overlap = function (target, callback) {
      //if(this.collider instanceof AABB && target.collider instanceof AABB)
      return this.AABBops('overlap', target, callback);
    };

    /**
    * Checks if the the sprite is overlapping another sprite or a group.
    * If the overlap is positive the current sprite will be displace by
    * the colliding one in the closest non-overlapping position.
    *
    * The check is performed using the colliders. If colliders are not set
    * they will be created automatically from the image/animation bounding box.
    *
    * A callback function can be specified to perform additional operations
    * when the collision occours.
    * If the target is a group the function will be called for each single
    * sprite colliding. The parameter of the function are respectively the
    * current sprite and the colliding sprite.
    *
    * @example
    *     sprite.collide(otherSprite, explosion);
    *
    *     function explosion(spriteA, spriteB) {
    *       spriteA.remove();
    *       spriteB.score++;
    *     }
    *
    * @method collide
    * @param {Object} target Sprite or group to check against the current one
    * @param {Function} [callback] The function to be called if overlap is positive
    * @return {Boolean} True if overlapping
    */
    this.collide = function (target, callback) {
      //if(this.collider instanceof AABB && target.collider instanceof AABB)
      return this.AABBops('collide', target, callback);
    };

    /**
    * Checks if the the sprite is overlapping another sprite or a group.
    * If the overlap is positive the current sprite will displace
    * the colliding one to the closest non-overlapping position.
    *
    * The check is performed using the colliders. If colliders are not set
    * they will be created automatically from the image/animation bounding box.
    *
    * A callback function can be specified to perform additional operations
    * when the collision occours.
    * If the target is a group the function will be called for each single
    * sprite colliding. The parameter of the function are respectively the
    * current sprite and the colliding sprite.
    *
    * @example
    *     sprite.displace(otherSprite, explosion);
    *
    *     function explosion(spriteA, spriteB) {
    *       spriteA.remove();
    *       spriteB.score++;
    *     }
    *
    * @method displace
    * @param {Object} target Sprite or group to check against the current one
    * @param {Function} [callback] The function to be called if overlap is positive
    * @return {Boolean} True if overlapping
    */
    this.displace = function (target, callback) {
      return this.AABBops('displace', target, callback);
    };

    /**
    * Checks if the the sprite is overlapping another sprite or a group.
    * If the overlap is positive the sprites will bounce affecting each
    * other's trajectories depending on their .velocity, .mass and .restitution
    *
    * The check is performed using the colliders. If colliders are not set
    * they will be created automatically from the image/animation bounding box.
    *
    * A callback function can be specified to perform additional operations
    * when the collision occours.
    * If the target is a group the function will be called for each single
    * sprite colliding. The parameter of the function are respectively the
    * current sprite and the colliding sprite.
    *
    * @example
    *     sprite.bounce(otherSprite, explosion);
    *
    *     function explosion(spriteA, spriteB) {
    *       spriteA.remove();
    *       spriteB.score++;
    *     }
    *
    * @method bounce
    * @param {Object} target Sprite or group to check against the current one
    * @param {Function} [callback] The function to be called if overlap is positive
    * @return {Boolean} True if overlapping
    */
    this.bounce = function (target, callback) {
      return this.AABBops('bounce', target, callback);
    };

    // Internal collision detection function. Do not use directly.
    this.AABBops = function (type, target, callback) {

      this.touching.left = false;
      this.touching.right = false;
      this.touching.top = false;
      this.touching.bottom = false;

      var result = false;

      //if single sprite turn into array anyway
      var others = [];

      if (target instanceof Sprite)
        others.push(target);
      else if (target instanceof Array) {
        if (quadTree !== undefined && quadTree.active)
          others = quadTree.retrieveFromGroup(this, target);

        if (others.length === 0)
          others = target;

      }
      else
        throw ('Error: overlap can only be checked between sprites or groups');

      for (var i = 0; i < others.length; i++)
        if (this !== others[i] && !this.removed) //you can check collisions within the same group but not on itself
        {
          var displacement;
          var other = others[i];

          if (this.collider === undefined)
            this.setDefaultCollider();

          if (other.collider === undefined)
            other.setDefaultCollider();

          /*
          if(this.colliderType=="default" && animations[currentAnimation]!=null)
          {
            print("busted");
            return false;
          }*/
          if (this.collider !== undefined && other.collider !== undefined) {
            if (type === 'overlap') {
              var over;

              //if the other is a circle I calculate the displacement from here
              if (this.collider instanceof CircleCollider)
                over = other.collider.overlap(this.collider);
              else
                over = this.collider.overlap(other.collider);

              if (over) {

                result = true;

                if (callback !== undefined && typeof callback === 'function')
                  callback.call(this, this, other);
              }
            }
            else if (type === 'collide' || type === 'displace' || type === 'bounce') {
              displacement = createVector(0, 0);

              //if the sum of the speed is more than the collider i may
              //have a tunnelling problem
              var tunnelX = abs(this.velocity.x - other.velocity.x) >= other.collider.extents.x / 2 && round(this.deltaX - this.velocity.x) === 0;

              var tunnelY = abs(this.velocity.y - other.velocity.y) >= other.collider.size().y / 2 && round(this.deltaY - this.velocity.y) === 0;


              if (tunnelX || tunnelY) {
                //instead of using the colliders I use the bounding box
                //around the previous position and current position
                //this is regardless of the collider type

                //the center is the average of the coll centers
                var c = createVector(
                  (this.position.x + this.previousPosition.x) / 2,
                  (this.position.y + this.previousPosition.y) / 2);

                //the extents are the distance between the coll centers
                //plus the extents of both
                var e = createVector(
                  abs(this.position.x - this.previousPosition.x) + this.collider.extents.x,
                  abs(this.position.y - this.previousPosition.y) + this.collider.extents.y);

                var bbox = new AABB(pInst, c, e, this.collider.offset);

                //bbox.draw();

                if (bbox.overlap(other.collider)) {
                  if (tunnelX) {

                    //entering from the right
                    if (this.velocity.x < 0)
                      displacement.x = other.collider.right() - this.collider.left() + 1;
                    else if (this.velocity.x > 0)
                      displacement.x = other.collider.left() - this.collider.right() - 1;
                  }

                  if (tunnelY) {
                    //from top
                    if (this.velocity.y > 0)
                      displacement.y = other.collider.top() - this.collider.bottom() - 1;
                    else if (this.velocity.y < 0)
                      displacement.y = other.collider.bottom() - this.collider.top() + 1;

                  }

                }//end overlap

              }
              else //non tunnel overlap
              {

                //if the other is a circle I calculate the displacement from here
                //and reverse it
                if (this.collider instanceof CircleCollider) {
                  displacement = other.collider.collide(this.collider).mult(-1);
                }
                else
                  displacement = this.collider.collide(other.collider);

              }

              if (displacement.x !== 0 || displacement.y !== 0) {
                var newVelX1, newVelY1, newVelX2, newVelY2;

                if (type === 'displace' && !other.immovable) {
                  other.position.sub(displacement);
                } else if ((type === 'collide' || type === 'bounce') && !this.immovable) {
                  this.position.add(displacement);
                  this.previousPosition = createVector(this.position.x, this.position.y);
                  this.newPosition = createVector(this.position.x, this.position.y);
                }

                if (displacement.x > 0)
                  this.touching.left = true;
                if (displacement.x < 0)
                  this.touching.right = true;
                if (displacement.y < 0)
                  this.touching.bottom = true;
                if (displacement.y > 0)
                  this.touching.top = true;

                if (type === 'bounce') {
                  if (this.collider instanceof CircleCollider && other.collider instanceof CircleCollider) {
                    var dx1 = p5.Vector.sub(this.position, other.position);
                    var dx2 = p5.Vector.sub(other.position, this.position);
                    var magnitude = dx1.magSq();
                    var totalMass = this.mass + other.mass;
                    var m1 = 0, m2 = 0;
                    if (this.immovable) {
                      m2 = 2;
                    } else if (other.immovable) {
                      m1 = 2;
                    } else {
                      m1 = 2 * other.mass / totalMass;
                      m2 = 2 * this.mass / totalMass;
                    }
                    var newVel1 = dx1.mult(m1 * p5.Vector.sub(this.velocity, other.velocity).dot(dx1) / magnitude);
                    var newVel2 = dx2.mult(m2 * p5.Vector.sub(other.velocity, this.velocity).dot(dx2) / magnitude);

                    this.velocity.sub(newVel1.mult(this.restitution));
                    other.velocity.sub(newVel2.mult(other.restitution));
                  }
                  else {
                    if (other.immovable) {
                      newVelX1 = -this.velocity.x + other.velocity.x;
                      newVelY1 = -this.velocity.y + other.velocity.y;
                    }
                    else {
                      newVelX1 = (this.velocity.x * (this.mass - other.mass) + (2 * other.mass * other.velocity.x)) / (this.mass + other.mass);
                      newVelY1 = (this.velocity.y * (this.mass - other.mass) + (2 * other.mass * other.velocity.y)) / (this.mass + other.mass);
                      newVelX2 = (other.velocity.x * (other.mass - this.mass) + (2 * this.mass * this.velocity.x)) / (this.mass + other.mass);
                      newVelY2 = (other.velocity.y * (other.mass - this.mass) + (2 * this.mass * this.velocity.y)) / (this.mass + other.mass);
                    }

                    //var bothCircles = (this.collider instanceof CircleCollider &&
                    //                   other.collider  instanceof CircleCollider);

                    //if(this.touching.left || this.touching.right || this.collider instanceof CircleCollider)

                    //print(displacement);

                    if (abs(displacement.x) > abs(displacement.y)) {


                      if (!this.immovable) {
                        this.velocity.x = newVelX1 * this.restitution;

                      }

                      if (!other.immovable)
                        other.velocity.x = newVelX2 * other.restitution;

                    }
                    //if(this.touching.top || this.touching.bottom || this.collider instanceof CircleCollider)
                    if (abs(displacement.x) < abs(displacement.y)) {

                      if (!this.immovable)
                        this.velocity.y = newVelY1 * this.restitution;

                      if (!other.immovable)
                        other.velocity.y = newVelY2 * other.restitution;
                    }
                  }
                }
                //else if(type == "collide")
                //this.velocity = createVector(0,0);

                if (callback !== undefined && typeof callback === 'function')
                  callback.call(this, this, other);

                result = true;
              }
            }
          }//end collider exists
        }

      return result;
    };
  } //end Sprite class

  defineLazyP5Property('Sprite', boundConstructorFactory(Sprite));

  /**
     * A camera facilitates scrolling and zooming for scenes extending beyond
     * the canvas. A camera has a position, a zoom factor, and the mouse
     * coordinates relative to the view.
     * The camera is automatically created on the first draw cycle.
     *
     * In p5.js terms the camera wraps the whole drawing cycle in a
     * transformation matrix but it can be disable anytime during the draw
     * cycle for example to draw interface elements in an absolute position.
     *
     * @class Camera
     * @constructor
     * @param {Number} x Initial x coordinate
     * @param {Number} y Initial y coordinate
     * @param {Number} zoom magnification
     **/
  function Camera(pInst, x, y, zoom) {
    /**
    * Camera position. Defines the global offset of the sketch.
    *
    * @property position
    * @type {p5.Vector}
    */
    this.position = pInst.createVector(x, y);

    /**
    * Camera zoom. Defines the global scale of the sketch.
    * A scale of 1 will be the normal size. Setting it to 2 will make everything
    * twice the size. .5 will make everything half size.
    *
    * @property zoom
    * @type {Number}
    */
    this.zoom = zoom;

    /**
    * MouseX translated to the camera view.
    * Offsetting and scaling the canvas will not change the sprites' position
    * nor the mouseX and mouseY variables. Use this property to read the mouse
    * position if the camera moved or zoomed.
    *
    * @property mouseX
    * @type {Number}
    */
    this.mouseX = pInst.mouseX;

    /**
    * MouseY translated to the camera view.
    * Offsetting and scaling the canvas will not change the sprites' position
    * nor the mouseX and mouseY variables. Use this property to read the mouse
    * position if the camera moved or zoomed.
    *
    * @property mouseY
    * @type {Number}
    */
    this.mouseY = pInst.mouseY;

    /**
    * True if the camera is active.
    * Read only property. Use the methods Camera.on() and Camera.off()
    * to enable or disable the camera.
    *
    * @property active
    * @type {Boolean}
    */
    this.active = false;

    /**
    * Activates the camera.
    * The canvas will be drawn according to the camera position and scale until
    * Camera.off() is called
    *
    * @method on
    */
    this.on = function () {
      if (!this.active) {
        cameraPush.call(pInst);
        this.active = true;
      }
    };

    /**
    * Deactivates the camera.
    * The canvas will be drawn normally, ignoring the camera's position
    * and scale until Camera.on() is called
    *
    * @method off
    */
    this.off = function () {
      if (this.active) {
        cameraPop.call(pInst);
        this.active = false;
      }
    };
  } //end camera class

  defineLazyP5Property('Camera', boundConstructorFactory(Camera));

  //called pre draw by default
  function cameraPush() {
    var pInst = this;
    var camera = pInst.camera;

    //awkward but necessary in order to have the camera at the center
    //of the canvas by default
    if (!camera.init && camera.position.x === 0 && camera.position.y === 0) {
      camera.position.x = pInst.width / 2;
      camera.position.y = pInst.height / 2;
      camera.init = true;
    }

    camera.mouseX = pInst.mouseX + camera.position.x - pInst.width / 2;
    camera.mouseY = pInst.mouseY + camera.position.y - pInst.height / 2;

    if (!camera.active) {
      camera.active = true;
      pInst.push();
      pInst.scale(camera.zoom);
      pInst.translate(-camera.position.x + pInst.width / 2 / camera.zoom, -camera.position.y + pInst.height / 2 / camera.zoom);
    }
  }

  //called postdraw by default
  function cameraPop() {
    var pInst = this;

    if (pInst.camera.active) {
      pInst.pop();
      pInst.camera.active = false;
    }
  }




  /**
     * In p5.play groups are collections of sprites with similar behavior.
     * For example a group may contain all the sprites in the background
     * or all the sprites that "kill" the player.
     *
     * Groups are "extended" arrays and inherit all their properties
     * e.g. group.length
     *
     * Since groups contain only references, a sprite can be in multiple
     * groups and deleting a group doesn't affect the sprites themselves.
     *
     * Sprite.remove() will also remove the sprite from all the groups
     * it belongs to.
     *
     * @class Group
     * @constructor
     */
  function Group() {

    //basically extending the array
    var array = [];

    /**
    * Gets the member at index i.
    *
    * @method get
    * @param {Number} i The index of the object to retrieve
    */
    array.get = function (i) {
      return array[i];
    };

    /**
    * Checks if the group contains a sprite.
    *
    * @method contains
    * @param {Sprite} sprite The sprite to search
    * @return {Number} Index or -1 if not found
    */
    array.contains = function (sprite) {
      return this.indexOf(sprite) > -1;
    };

    /**
     * Same as Group.contains
     * @method indexOf
     */
    array.indexOf = function (item) {
      for (var i = 0, len = array.length; i < len; ++i) {
        if (virtEquals(item, array[i])) {
          return i;
        }
      }
      return -1;
    };

    /**
    * Adds a sprite to the group.
    *
    * @method add
    * @param {Sprite} s The sprite to be added
    */
    array.add = function (s) {
      if (!(s instanceof Sprite)) {
        throw ('Error: you can only add sprites to a group');
      }

      if (-1 === this.indexOf(s)) {
        array.push(s);
        s.groups.push(this);
      }
    };

    /**
     * Same as group.length
     * @method size
     */
    array.size = function () {
      return array.length;
    };

    /**
    * Removes all the sprites in the group
    * from the scene.
    *
    * @method removeSprites
    */
    array.removeSprites = function () {
      while (array.length > 0) {
        array[0].remove();
      }
    };

    /**
    * Removes all references to the group.
    * Does not remove the actual sprites.
    *
    * @method clear
    */
    array.clear = function () {
      array.length = 0;
    };

    /**
    * Removes a sprite from the group.
    * Does not remove the actual sprite, only the affiliation (reference).
    *
    * @method remove
    * @param {Sprite} item The sprite to be removed
    * @return {Boolean} True if sprite was found and removed
    */
    array.remove = function (item) {
      if (!(item instanceof Sprite)) {
        throw ('Error: you can only remove sprites from a group');
      }

      var i, removed = false;
      for (i = array.length - 1; i >= 0; i--) {
        if (array[i] === item) {
          array.splice(i, 1);
          removed = true;
        }
      }

      if (removed) {
        for (i = item.groups.length - 1; i >= 0; i--) {
          if (item.groups[i] === this) {
            item.groups.splice(i, 1);
          }
        }
      }

      return removed;
    };

    /**
     * Returns a copy of the group as standard array.
     * @method toArray
     */
    array.toArray = function () {
      return array.slice(0);
    };

    /**
    * Returns the highest depth in a group
    *
    * @method maxDepth
    * @return {Number} The depth of the sprite drawn on the top
    */
    array.maxDepth = function () {
      if (array.length === 0) {
        return 0;
      }

      return array.reduce(function (maxDepth, sprite) {
        return Math.max(maxDepth, sprite.depth);
      }, -Infinity);
    };

    /**
    * Returns the lowest depth in a group
    *
    * @method minDepth
    * @return {Number} The depth of the sprite drawn on the bottom
    */
    array.minDepth = function () {
      if (array.length === 0) {
        return 99999;
      }

      return array.reduce(function (minDepth, sprite) {
        return Math.min(minDepth, sprite.depth);
      }, Infinity);
    };

    /**
    * Draws all the sprites in the group.
    *
    * @method draw
    */
    array.draw = function () {

      //sort by depth
      this.sort(function (a, b) {
        return a.depth - b.depth;
      });

      for (var i = 0; i < this.size(); i++) {
        this.get(i).display();
      }
    };

    //internal use
    function virtEquals(obj, other) {
      if (obj === null || other === null) {
        return (obj === null) && (other === null);
      }
      if (typeof (obj) === 'string') {
        return obj === other;
      }
      if (typeof (obj) !== 'object') {
        return obj === other;
      }
      if (obj.equals instanceof Function) {
        return obj.equals(other);
      }
      return obj === other;
    }

    /**
     * Collide each member of group against the target using the given collision
     * type.  Return true if any collision occurred.
     * Internal use
     *
     * @private
     * @method _groupCollide
     * @param {!string} type one of 'overlap', 'collide', 'displace', 'bounce'
     * @param {Object} target Group or Sprite
     * @param {Function} [callback] on collision.
     * @return {boolean} True if any collision/overlap occurred
     */
    function _groupCollide(type, target, callback) {
      var didCollide = false;
      for (var i = 0; i < this.size(); i++)
        didCollide = this.get(i).AABBops(type, target, callback) || didCollide;
      return didCollide;
    }

    /**
    * Checks if the the group is overlapping another group or sprite.
    * The check is performed using the colliders. If colliders are not set
    * they will be created automatically from the image/animation bounding box.
    *
    * A callback function can be specified to perform additional operations
    * when the overlap occurs.
    * The function will be called for each single sprite overlapping.
    * The parameter of the function are respectively the
    * member of the current group and the other sprite passed as parameter.
    *
    * @example
    *     group.overlap(otherSprite, explosion);
    *
    *     function explosion(spriteA, spriteB) {
    *       spriteA.remove();
    *       spriteB.score++;
    *     }
    *
    * @method overlap
    * @param {Object} target Group or Sprite to check against the current one
    * @param {Function} [callback] The function to be called if overlap is positive
    * @return {Boolean} True if overlapping
    */
    array.overlap = _groupCollide.bind(array, 'overlap');


    /**
    * Checks if the the group is overlapping another group or sprite.
    * If the overlap is positive the sprites in the group will be displaced
    * by the colliding one to the closest non-overlapping positions.
    *
    * The check is performed using the colliders. If colliders are not set
    * they will be created automatically from the image/animation bounding box.
    *
    * A callback function can be specified to perform additional operations
    * when the overlap occours.
    * The function will be called for each single sprite overlapping.
    * The parameter of the function are respectively the
    * member of the current group and the other sprite passed as parameter.
    *
    * @example
    *     group.collide(otherSprite, explosion);
    *
    *     function explosion(spriteA, spriteB) {
    *       spriteA.remove();
    *       spriteB.score++;
    *     }
    *
    * @method collide
    * @param {Object} target Group or Sprite to check against the current one
    * @param {Function} [callback] The function to be called if overlap is positive
    * @return {Boolean} True if overlapping
    */
    array.collide = _groupCollide.bind(array, 'collide');

    /**
    * Checks if the the group is overlapping another group or sprite.
    * If the overlap is positive the sprites in the group will displace
    * the colliding ones to the closest non-overlapping positions.
    *
    * The check is performed using the colliders. If colliders are not set
    * they will be created automatically from the image/animation bounding box.
    *
    * A callback function can be specified to perform additional operations
    * when the overlap occurs.
    * The function will be called for each single sprite overlapping.
    * The parameter of the function are respectively the
    * member of the current group and the other sprite passed as parameter.
    *
    * @example
    *     group.displace(otherSprite, explosion);
    *
    *     function explosion(spriteA, spriteB) {
    *       spriteA.remove();
    *       spriteB.score++;
    *     }
    *
    * @method displace
    * @param {Object} target Group or Sprite to check against the current one
    * @param {Function} [callback] The function to be called if overlap is positive
    * @return {Boolean} True if overlapping
    */
    array.displace = _groupCollide.bind(array, 'displace');

    /**
    * Checks if the the group is overlapping another group or sprite.
    * If the overlap is positive the sprites will bounce affecting each
    * other's trajectories depending on their .velocity, .mass and .restitution.
    *
    * The check is performed using the colliders. If colliders are not set
    * they will be created automatically from the image/animation bounding box.
    *
    * A callback function can be specified to perform additional operations
    * when the overlap occours.
    * The function will be called for each single sprite overlapping.
    * The parameter of the function are respectively the
    * member of the current group and the other sprite passed as parameter.
    *
    * @example
    *     group.bounce(otherSprite, explosion);
    *
    *     function explosion(spriteA, spriteB) {
    *       spriteA.remove();
    *       spriteB.score++;
    *     }
    *
    * @method bounce
    * @param {Object} target Group or Sprite to check against the current one
    * @param {Function} [callback] The function to be called if overlap is positive
    * @return {Boolean} True if overlapping
    */
    array.bounce = _groupCollide.bind(array, 'bounce');

    return array;
  }

  p5.prototype.Group = Group;

  //circle collider - used internally
  function CircleCollider(pInst, _center, _radius, _offset) {
    var pInstBind = createPInstBinder(pInst);

    var createVector = pInstBind('createVector');

    var CENTER = p5.prototype.CENTER;

    this.center = _center;
    this.radius = _radius;
    this.originalRadius = _radius;

    if (_offset === undefined)
      this.offset = createVector(0, 0);
    else
      this.offset = _offset;
    this.extents = createVector(_radius * 2, _radius * 2);

    this.draw = function () {
      pInst.noFill();
      pInst.stroke(0, 255, 0);
      pInst.rectMode(CENTER);
      pInst.ellipse(this.center.x + this.offset.x, this.center.y + this.offset.y, this.radius * 2, this.radius * 2);
    };

    //should be called only for circle vs circle
    this.overlap = function (other) {
      //square dist
      var r = this.radius + other.radius;
      r *= r;
      var thisCenterX = this.center.x + this.offset.x;
      var thisCenterY = this.center.y + this.offset.y;
      var otherCenterX = other.center.x + other.offset.x;
      var otherCenterY = other.center.y + other.offset.y;
      var sqDist = pow(thisCenterX - otherCenterX, 2) + pow(thisCenterY - otherCenterY, 2);
      return r > sqDist;
    };

    //should be called only for circle vs circle
    this.collide = function (other) {
      if (this.overlap(other)) {
        var thisCenterX = this.center.x + this.offset.x;
        var thisCenterY = this.center.y + this.offset.y;
        var otherCenterX = other.center.x + other.offset.x;
        var otherCenterY = other.center.y + other.offset.y;
        var a = pInst.atan2(thisCenterY - otherCenterY, thisCenterX - otherCenterX);
        var radii = this.radius + other.radius;
        var intersection = abs(radii - dist(thisCenterX, thisCenterY, otherCenterX, otherCenterY));

        var displacement = createVector(pInst.cos(a) * intersection, pInst.sin(a) * intersection);

        return displacement;
      } else {
        return createVector(0, 0);
      }
    };

    this.size = function () {
      return createVector(this.radius * 2, this.radius * 2);
    };

    this.left = function () {
      return this.center.x + this.offset.x - this.radius;
    };

    this.right = function () {
      return this.center.x + this.offset.x + this.radius;
    };

    this.top = function () {
      return this.center.y + this.offset.y - this.radius;
    };

    this.bottom = function () {
      return this.center.y + this.offset.y + this.radius;
    };



  }
  defineLazyP5Property('CircleCollider', boundConstructorFactory(CircleCollider));

  //axis aligned bounding box - extents are the half sizes - used internally
  function AABB(pInst, _center, _extents, _offset) {
    var pInstBind = createPInstBinder(pInst);

    var createVector = pInstBind('createVector');

    var CENTER = p5.prototype.CENTER;
    var PI = p5.prototype.PI;

    this.center = _center;
    this.extents = _extents;
    this.originalExtents = _extents.copy();

    if (_offset === undefined)
      this.offset = createVector(0, 0);
    else
      this.offset = _offset;

    this.min = function () {
      return createVector(this.center.x + this.offset.x - this.extents.x, this.center.y + this.offset.y - this.extents.y);
    };

    this.max = function () {
      return createVector(this.center.x + this.offset.x + this.extents.x, this.center.y + this.offset.y + this.extents.y);
    };

    this.right = function () {
      return this.center.x + this.offset.x + this.extents.x / 2;
    };

    this.left = function () {
      return this.center.x + this.offset.x - this.extents.x / 2;
    };

    this.top = function () {
      return this.center.y + this.offset.y - this.extents.y / 2;
    };

    this.bottom = function () {
      return this.center.y + this.offset.y + this.extents.y / 2;
    };

    this.size = function () {
      return createVector(this.extents.x * 2, this.extents.y * 2);
    };

    this.rotate = function (r) {
      //rotate the bbox
      var t;
      if (pInst._angleMode === pInst.RADIANS) {
        t = radians(r);
      } else {
        t = r;
      }

      var w2 = this.extents.x * abs(pInst.cos(t)) + this.extents.y * abs(pInst.sin(t));
      var h2 = this.extents.x * abs(pInst.sin(t)) + this.extents.y * abs(pInst.cos(t));

      this.extents.x = w2;
      this.extents.y = h2;

    };

    this.draw = function () {
      //fill(col);
      pInst.noFill();
      pInst.stroke(0, 255, 0);
      pInst.rectMode(CENTER);
      pInst.rect(this.center.x + this.offset.x, this.center.y + this.offset.y, this.size().x / 2, this.size().y / 2);
    };

    this.overlap = function (other) {
      //box vs box
      if (other instanceof AABB) {
        var md = other.minkowskiDifference(this);

        if (md.min().x <= 0 &&
          md.max().x >= 0 &&
          md.min().y <= 0 &&
          md.max().y >= 0) {
          return true;
        }
        else
          return false;
      }
      //box vs circle
      else if (other instanceof CircleCollider) {

        //find closest point to the circle on the box
        var pt = createVector(other.center.x, other.center.y);

        //I don't know what's going o try to trace a line from centers to see
        if (other.center.x < this.left())
          pt.x = this.left();
        else if (other.center.x > this.right())
          pt.x = this.right();

        if (other.center.y < this.top())
          pt.y = this.top();
        else if (other.center.y > this.bottom())
          pt.y = this.bottom();

        var distance = pt.dist(other.center);

        return distance < other.radius;
      }
    };

    this.collide = function (other) {

      if (other instanceof AABB) {
        var md = other.minkowskiDifference(this);

        if (md.min().x <= 0 &&
          md.max().x >= 0 &&
          md.min().y <= 0 &&
          md.max().y >= 0) {
          var boundsPoint = md.closestPointOnBoundsToPoint(createVector(0, 0));

          return boundsPoint;
        }
        else
          return createVector(0, 0);
      }
      //box vs circle
      else if (other instanceof CircleCollider) {

        //find closest point to the circle on the box
        var pt = createVector(other.center.x, other.center.y);

        //I don't know what's going o try to trace a line from centers to see
        if (other.center.x < this.left())
          pt.x = this.left();
        else if (other.center.x > this.right())
          pt.x = this.right();

        if (other.center.y < this.top())
          pt.y = this.top();
        else if (other.center.y > this.bottom())
          pt.y = this.bottom();


        var distance = pt.dist(other.center);
        var a;

        if (distance < other.radius) {
          //reclamp point
          if (pt.x === other.center.x && pt.y === other.center.y) {
            var xOverlap = pt.x - this.center.x;
            var yOverlap = pt.y - this.center.y;


            if (abs(xOverlap) < abs(yOverlap)) {
              if (xOverlap > 0)
                pt.x = this.right();
              else
                pt.x = this.left();
            }
            else {
              if (yOverlap < 0)
                pt.y = this.top();
              else
                pt.y = this.bottom();
            }

            a = pInst.atan2(other.center.y - pt.y, other.center.x - pt.x);

            //fix exceptions
            if (a === 0) {
              if (pt.x === this.right()) a = PI;
              if (pt.y === this.top()) a = PI / 2;
              if (pt.y === this.bottom()) a = -PI / 2;
            }
          }
          else {
            //angle bw point and center
            a = pInst.atan2(pt.y - other.center.y, pt.x - other.center.x);
            //project the normal (line between pt and center) onto the circle
          }

          var d = createVector(pt.x - other.center.x, pt.y - other.center.y);
          var displacement = createVector(pInst.cos(a) * other.radius - d.x, pInst.sin(a) * other.radius - d.y);

          //if(pt.x === other.center.x && pt.y === other.center.y)
          //displacement = displacement.mult(-1);

          return displacement;
          //return createVector(0,0);
        }
        else
          return createVector(0, 0);
      }
    };

    this.minkowskiDifference = function (other) {
      var topLeft = this.min().sub(other.max());
      var fullSize = this.size().add(other.size());
      return new AABB(pInst, topLeft.add(fullSize.div(2)), fullSize.div(2));
    };


    this.closestPointOnBoundsToPoint = function (point) {
      // test x first
      var minDist = abs(point.x - this.min().x);
      var boundsPoint = createVector(this.min().x, point.y);

      if (abs(this.max().x - point.x) < minDist) {
        minDist = abs(this.max().x - point.x);
        boundsPoint = createVector(this.max().x, point.y);
      }

      if (abs(this.max().y - point.y) < minDist) {
        minDist = abs(this.max().y - point.y);
        boundsPoint = createVector(point.x, this.max().y);
      }

      if (abs(this.min().y - point.y) < minDist) {
        minDist = abs(this.min.y - point.y);
        boundsPoint = createVector(point.x, this.min().y);
      }

      return boundsPoint;
    };


  }//end AABB
  defineLazyP5Property('AABB', boundConstructorFactory(AABB));



  /**
   * An Animation object contains a series of images (p5.Image) that
   * can be displayed sequentially.
   *
   * All files must be png images. You must include the directory from the sketch root,
   * and the extension .png
   *
   * A sprite can have multiple labeled animations, see Sprite.addAnimation
   * and Sprite.changeAnimation, however an animation can be used independently.
   *
   * An animation can be created either by passing a series of file names,
   * no matter how many or by passing the first and the last file name
   * of a numbered sequence.
   * p5.play will try to detect the sequence pattern.
   *
   * For example if the given filenames are
   * "data/file0001.png" and "data/file0005.png" the images
   * "data/file0003.png" and "data/file0004.png" will be loaded as well.
   *
   * @example
   *     var sequenceAnimation;
   *     var glitch;
   *
   *     function preload() {
   *       sequenceAnimation = loadAnimation("data/walking0001.png", "data/walking0005.png");
   *       glitch = loadAnimation("data/dog.png", "data/horse.png", "data/cat.png", "data/snake.png");
   *     }
   *
   *     function setup() {
   *       createCanvas(800, 600);
   *     }
   *
   *     function draw() {
   *       background(0);
   *       animation(sequenceAnimation, 100, 100);
   *       animation(glitch, 200, 100);
   *     }
   *
   * @class Animation
   * @constructor
   * @param {String} fileName1 First file in a sequence OR first image file
   * @param {String} fileName2 Last file in a sequence OR second image file
   * @param {String} [...fileNameN] Any number of image files after the first two
   */
  function Animation(pInst) {
    var frameArguments = Array.prototype.slice.call(arguments, 1);
    var i;

    var CENTER = p5.prototype.CENTER;

    /**
    * Array of frames (p5.Image)
    *
    * @property images
    * @type {Array}
    */
    this.images = [];

    var frame = 0;
    var cycles = 0;
    var targetFrame = -1;

    this.offX = 0;
    this.offY = 0;

    /**
    * Delay between frames in number of draw cycles.
    * If set to 4 the framerate of the animation would be the
    * sketch framerate divided by 4 (60fps = 15fps)
    *
    * @property frameDelay
    * @type {Number}
    * @default 4
    */
    this.frameDelay = 4;

    /**
    * True if the animation is currently playing.
    *
    * @property playing
    * @type {Boolean}
    * @default true
    */
    this.playing = true;

    /**
    * Animation visibility.
    *
    * @property visible
    * @type {Boolean}
    * @default true
    */
    this.visible = true;

    /**
    * If set to false the animation will stop after reaching the last frame
    *
    * @property looping
    * @type {Boolean}
    * @default true
    */
    this.looping = true;

    /**
    * True if frame changed during the last draw cycle
    *
    * @property frameChanged
    * @type {Boolean}
    */
    this.frameChanged = false;

    //is the collider defined manually or defined
    //by the current frame size
    this.imageCollider = false;


    //sequence mode
    if (frameArguments.length === 2 && typeof frameArguments[0] === 'string' && typeof frameArguments[1] === 'string') {
      var from = frameArguments[0];
      var to = frameArguments[1];

      //print("sequence mode "+from+" -> "+to);

      //make sure the extensions are fine
      var ext1 = from.substring(from.length - 4, from.length);
      if (ext1 !== '.png') {
        pInst.print('Animation error: you need to use .png files (filename ' + from + ')');
        from = -1;
      }

      var ext2 = to.substring(to.length - 4, to.length);
      if (ext2 !== '.png') {
        pInst.print('Animation error: you need to use .png files (filename ' + to + ')');
        to = -1;
      }

      //extensions are fine
      if (from !== -1 && to !== -1) {
        var digits1 = 0;
        var digits2 = 0;

        //skip extension work backwards to find the numbers
        for (i = from.length - 5; i >= 0; i--) {
          if (from.charAt(i) >= '0' && from.charAt(i) <= '9')
            digits1++;
        }

        for (i = to.length - 5; i >= 0; i--) {
          if (to.charAt(i) >= '0' && to.charAt(i) <= '9')
            digits2++;
        }

        var prefix1 = from.substring(0, from.length - (4 + digits1));
        var prefix2 = to.substring(0, to.length - (4 + digits2));

        // Our numbers likely have leading zeroes, which means that some
        // browsers (e.g., PhantomJS) will interpret them as base 8 (octal)
        // instead of decimal. To fix this, we'll explicity tell parseInt to
        // use a base of 10 (decimal). For more details on this issue, see
        // http://stackoverflow.com/a/8763427/2422398.
        var number1 = parseInt(from.substring(from.length - (4 + digits1), from.length - 4), 10);
        var number2 = parseInt(to.substring(to.length - (4 + digits2), to.length - 4), 10);

        //swap if inverted
        if (number2 < number1) {
          var t = number2;
          number2 = number1;
          number1 = t;
        }

        //two different frames
        if (prefix1 !== prefix2) {
          //print("2 separate images");
          this.images.push(pInst.loadImage(from));
          this.images.push(pInst.loadImage(to));
        }
        //same digits: case img0001, img0002
        else {
          var fileName;
          if (digits1 === digits2) {

            //load all images
            for (i = number1; i <= number2; i++) {
              // Use nf() to number format 'i' into four digits
              fileName = prefix1 + pInst.nf(i, digits1) + '.png';
              this.images.push(pInst.loadImage(fileName));

            }

          }
          else //case: case img1, img2
          {
            //print("from "+prefix1+" "+number1 +" to "+number2);
            for (i = number1; i <= number2; i++) {
              // Use nf() to number format 'i' into four digits
              fileName = prefix1 + i + '.png';
              this.images.push(pInst.loadImage(fileName));

            }

          }
        }

      }//end no ext error

    }//end sequence mode
    // Sprite sheet mode
    else if (frameArguments.length === 1 && (frameArguments[0] instanceof SpriteSheet)) {
      this.spriteSheet = frameArguments[0];
      this.images = this.spriteSheet.frames;
    }
    else if (frameArguments.length !== 0)//arbitrary list of images
    {
      //print("Animation arbitrary mode");
      for (i = 0; i < frameArguments.length; i++) {
        //print("loading "+fileNames[i]);
        if (frameArguments[i] instanceof p5.Image)
          this.images.push(frameArguments[i]);
        else
          this.images.push(pInst.loadImage(frameArguments[i]));
      }
    }

    /**
    * Objects are passed by reference so to have different sprites
    * using the same animation you need to clone it.
    *
    * @method clone
    * @return {Animation} A clone of the current animation
    */
    this.clone = function () {
      var myClone = new Animation(pInst); //empty
      myClone.images = [];

      if (this.spriteSheet) {
        myClone.spriteSheet = this.spriteSheet.clone();
      }
      myClone.images = this.images.slice();

      myClone.offX = this.offX;
      myClone.offY = this.offY;
      myClone.frameDelay = this.frameDelay;
      myClone.playing = this.playing;
      myClone.looping = this.looping;

      return myClone;
    };

    /**
     * Draws the animation at coordinate x and y.
     * Updates the frames automatically.
     *
     * @method draw
     * @param {Number} x x coordinate
     * @param {Number} y y coordinate
     * @param {Number} [r=0] rotation
     */
    this.draw = function (x, y, r) {
      this.xpos = x;
      this.ypos = y;
      this.rotation = r || 0;

      if (this.visible) {

        //only connection with the sprite class
        //if animation is used independently draw and update are the sam
        if (!this.isSpriteAnimation)
          this.update();

        //this.currentImageMode = g.imageMode;
        pInst.push();
        pInst.imageMode(CENTER);

        pInst.translate(this.xpos, this.ypos);
        if (pInst._angleMode === pInst.RADIANS) {
          pInst.rotate(radians(this.rotation));
        } else {
          pInst.rotate(this.rotation);
        }

        if (this.images[frame] !== undefined) {
          if (this.spriteSheet) {
            var frame_info = this.images[frame].frame;
            //pInst.image(this.spriteSheet.image, frame_info.x, frame_info.y, frame_info.width,
            //  frame_info.height, this.offX, this.offY, frame_info.width, frame_info.height);
            pInst.image(this.spriteSheet.image, this.offX, this.offY, frame_info.width, frame_info.height, frame_info.x, frame_info.y, frame_info.width, frame_info.height);


          } else {
            pInst.image(this.images[frame], this.offX, this.offY);
          }
        }
        else {
          pInst.print('Warning undefined frame ' + frame);
          //this.isActive = false;
        }

        pInst.pop();
      }
    };

    //called by draw
    this.update = function () {
      cycles++;
      var previousFrame = frame;
      this.frameChanged = false;


      //go to frame
      if (this.images.length === 1) {
        this.playing = false;
        frame = 0;
      }

      if (this.playing && cycles % this.frameDelay === 0) {
        //going to target frame up
        if (targetFrame > frame && targetFrame !== -1) {
          frame++;
        }
        //going to taget frame down
        else if (targetFrame < frame && targetFrame !== -1) {
          frame--;
        }
        else if (targetFrame === frame && targetFrame !== -1) {
          this.playing = false;
        }
        else if (this.looping) //advance frame
        {
          //if next frame is too high
          if (frame >= this.images.length - 1)
            frame = 0;
          else
            frame++;
        } else {
          //if next frame is too high
          if (frame < this.images.length - 1)
            frame++;
        }
      }

      if (previousFrame !== frame)
        this.frameChanged = true;

    };//end update

    /**
    * Plays the animation.
    *
    * @method play
    */
    this.play = function () {
      this.playing = true;
      targetFrame = -1;
    };

    /**
    * Stops the animation.
    *
    * @method stop
    */
    this.stop = function () {
      this.playing = false;
    };

    /**
    * Rewinds the animation to the first frame.
    *
    * @method rewind
    */
    this.rewind = function () {
      frame = 0;
    };

    /**
    * Changes the current frame.
    *
    * @method changeFrame
    * @param {Number} frame Frame number (starts from 0).
    */
    this.changeFrame = function (f) {
      if (f < this.images.length)
        frame = f;
      else
        frame = this.images.length - 1;

      targetFrame = -1;
      //this.playing = false;
    };

    /**
   * Goes to the next frame and stops.
   *
   * @method nextFrame
   */
    this.nextFrame = function () {

      if (frame < this.images.length - 1)
        frame = frame + 1;
      else if (this.looping)
        frame = 0;

      targetFrame = -1;
      this.playing = false;
    };

    /**
   * Goes to the previous frame and stops.
   *
   * @method previousFrame
   */
    this.previousFrame = function () {

      if (frame > 0)
        frame = frame - 1;
      else if (this.looping)
        frame = this.images.length - 1;

      targetFrame = -1;
      this.playing = false;
    };

    /**
    * Plays the animation forward or backward toward a target frame.
    *
    * @method goToFrame
    * @param {Number} toFrame Frame number destination (starts from 0)
    */
    this.goToFrame = function (toFrame) {
      if (toFrame < 0 || toFrame >= this.images.length) {
        return;
      }

      // targetFrame gets used by the update() method to decide what frame to
      // select next.  When it's not being used it gets set to -1.
      targetFrame = toFrame;

      if (targetFrame !== frame) {
        this.playing = true;
      }
    };

    /**
    * Returns the current frame number.
    *
    * @method getFrame
    * @return {Number} Current frame (starts from 0)
    */
    this.getFrame = function () {
      return frame;
    };

    /**
    * Returns the last frame number.
    *
    * @method getLastFrame
    * @return {Number} Last frame number (starts from 0)
    */
    this.getLastFrame = function () {
      return this.images.length - 1;
    };

    /**
    * Returns the current frame image as p5.Image.
    *
    * @method getFrameImage
    * @return {p5.Image} Current frame image
    */
    this.getFrameImage = function () {
      return this.images[frame];
    };

    /**
    * Returns the frame image at the specified frame number.
    *
    * @method getImageAt
    * @param {Number} frame Frame number
    * @return {p5.Image} Frame image
    */
    this.getImageAt = function (f) {
      return this.images[f];
    };

    /**
    * Returns the current frame width in pixels.
    * If there is no image loaded, returns 1.
    *
    * @method getWidth
    * @return {Number} Frame width
    */
    this.getWidth = function () {
      if (this.images[frame] instanceof p5.Image) {
        return this.images[frame].width;
      } else if (this.images[frame]) {
        // Special case: Animation-from-spritesheet treats its images array differently.
        return this.images[frame].frame.width;
      } else {
        return 1;
      }
    };

    /**
    * Returns the current frame height in pixels.
    * If there is no image loaded, returns 1.
    *
    * @method getHeight
    * @return {Number} Frame height
    */
    this.getHeight = function () {
      if (this.images[frame] instanceof p5.Image) {
        return this.images[frame].height;
      } else if (this.images[frame]) {
        // Special case: Animation-from-spritesheet treats its images array differently.
        return this.images[frame].frame.height;
      } else {
        return 1;
      }
    };

  }

  defineLazyP5Property('Animation', boundConstructorFactory(Animation));

  /**
   * Represents a sprite sheet and all it's frames.  To be used with Animation,
   * or static drawing single frames.
   *
   *  There are two different ways to load a SpriteSheet
   *
   * 1. Given width, height that will be used for every frame and the
   *    number of frames to cycle through. The sprite sheet must have a
   *    uniform grid with consistent rows and columns.
   *
   * 2. Given an array of frame objects that define the position and
   *    dimensions of each frame.  This is Flexible because you can use
   *    sprite sheets that don't have uniform rows and columns.
   *
   * @example
   *     // Method 1 - Using width, height for each frame and number of frames
   *     explode_sprite_sheet = loadSpriteSheet('assets/explode_sprite_sheet.png', 171, 158, 11);
   *
   *     // Method 2 - Using an array of objects that define each frame
   *     var player_frames = loadJSON('assets/tiles.json');
   *     player_sprite_sheet = loadSpriteSheet('assets/player_spritesheet.png', player_frames);
   *
   * @class SpriteSheet
   * @constructor
   * @param image String image path or p5.Image object
   */
  function SpriteSheet(pInst) {
    var spriteSheetArgs = Array.prototype.slice.call(arguments, 1);

    this.image = null;
    this.frames = [];
    this.frame_width = 0;
    this.frame_height = 0;
    this.num_frames = 0;

    /**
     * Generate the frames data for this sprite sheet baesd on user params
     * @private
     * @method _generateSheetFrames
     */
    this._generateSheetFrames = function () {
      var sX = 0, sY = 0;
      for (var i = 0; i < this.num_frames; i++) {
        this.frames.push(
          {
            'name': i,
            'frame': {
              'x': sX,
              'y': sY,
              'width': this.frame_width,
              'height': this.frame_height
            }
          });
        sX += this.frame_width;
        if (sX >= this.image.width) {
          sX = 0;
          sY += this.frame_height;
          if (sY >= this.image.height) {
            sY = 0;
          }
        }
      }
    };

    if (spriteSheetArgs.length === 2 && Array.isArray(spriteSheetArgs[1])) {
      this.frames = spriteSheetArgs[1];
      this.num_frames = this.frames.length;
    } else if (spriteSheetArgs.length === 4 &&
      (typeof spriteSheetArgs[1] === 'number') &&
      (typeof spriteSheetArgs[2] === 'number') &&
      (typeof spriteSheetArgs[3] === 'number')) {
      this.frame_width = spriteSheetArgs[1];
      this.frame_height = spriteSheetArgs[2];
      this.num_frames = spriteSheetArgs[3];
    }

    if (spriteSheetArgs[0] instanceof p5.Image) {
      this.image = spriteSheetArgs[0];
      if (spriteSheetArgs.length === 4) {
        this._generateSheetFrames();
      }
    } else {
      if (spriteSheetArgs.length === 2) {
        this.image = pInst.loadImage(spriteSheetArgs[0]);
      } else if (spriteSheetArgs.length === 4) {
        this.image = pInst.loadImage(spriteSheetArgs[0], this._generateSheetFrames.bind(this));
      }
    }

    /**
     * Draws a specific frame to the canvas.
     * @param frame_name  Can either be a string name, or a numeric index.
     * @param x   x position to draw the frame at
     * @param y   y position to draw the frame at
     * @param [width]   optional width to draw the frame
     * @param [height]  optional height to draw the frame
     * @method drawFrame
     */
    this.drawFrame = function (frame_name, x, y, width, height) {
      var frameToDraw;
      if (typeof frame_name === 'number') {
        frameToDraw = this.frames[frame_name].frame;
      } else {
        for (var i = 0; i < this.frames.length; i++) {
          if (this.frames[i].name === frame_name) {
            frameToDraw = this.frames[i].frame;
            break;
          }
        }
      }
      var dWidth = width || frameToDraw.width;
      var dHeight = height || frameToDraw.height;
      pInst.image(this.image, frameToDraw.x, frameToDraw.y,
        frameToDraw.width, frameToDraw.height, x, y, dWidth, dHeight);

      //pInst.image(this.image, x, y,
      //  frameToDraw.width, frameToDraw.height - 1, frameToDraw.x, frameToDraw.y, dWidth, dHeight);
    };

    /**
     * Objects are passed by reference so to have different sprites
     * using the same animation you need to clone it.
     *
     * @method clone
     * @return {SpriteSheet} A clone of the current SpriteSheet
     */
    this.clone = function () {
      var myClone = new SpriteSheet(pInst); //empty

      // Deep clone the frames by value not reference
      for (var i = 0; i < this.frames.length; i++) {
        var frame = this.frames[i].frame;
        var cloneFrame = {
          'name': frame.name,
          'frame': {
            'x': frame.x,
            'y': frame.y,
            'width': frame.width,
            'height': frame.height
          }
        };
        myClone.frames.push(cloneFrame);
      }

      // clone other fields
      myClone.image = this.image;
      myClone.frame_width = this.frame_width;
      myClone.frame_height = this.frame_height;
      myClone.num_frames = this.num_frames;

      return myClone;
    };
  }

  defineLazyP5Property('SpriteSheet', boundConstructorFactory(SpriteSheet));

  //general constructor to be able to feed arguments as array
  function construct(constructor, args) {
    function F() {
      return constructor.apply(this, args);
    }
    F.prototype = constructor.prototype;
    return new F();
  }





  /*
   * Javascript Quadtree
   * based on
   * https://github.com/timohausmann/quadtree-js/
   * Copyright © 2012 Timo Hausmann
  */

  function Quadtree(bounds, max_objects, max_levels, level) {

    this.active = true;
    this.max_objects = max_objects || 10;
    this.max_levels = max_levels || 4;

    this.level = level || 0;
    this.bounds = bounds;

    this.objects = [];
    this.object_refs = [];
    this.nodes = [];
  }

  Quadtree.prototype.updateBounds = function () {

    //find maximum area
    var objects = this.getAll();
    var x = 10000;
    var y = 10000;
    var w = -10000;
    var h = -10000;

    for (var i = 0; i < objects.length; i++) {
      if (objects[i].position.x < x)
        x = objects[i].position.x;
      if (objects[i].position.y < y)
        y = objects[i].position.y;
      if (objects[i].position.x > w)
        w = objects[i].position.x;
      if (objects[i].position.y > h)
        h = objects[i].position.y;
    }


    this.bounds = {
      x: x,
      y: y,
      width: w,
      height: h
    };
    //print(this.bounds);
  };

  /*
     * Split the node into 4 subnodes
     */
  Quadtree.prototype.split = function () {

    var nextLevel = this.level + 1,
      subWidth = Math.round(this.bounds.width / 2),
      subHeight = Math.round(this.bounds.height / 2),
      x = Math.round(this.bounds.x),
      y = Math.round(this.bounds.y);

    //top right node
    this.nodes[0] = new Quadtree({
      x: x + subWidth,
      y: y,
      width: subWidth,
      height: subHeight
    }, this.max_objects, this.max_levels, nextLevel);

    //top left node
    this.nodes[1] = new Quadtree({
      x: x,
      y: y,
      width: subWidth,
      height: subHeight
    }, this.max_objects, this.max_levels, nextLevel);

    //bottom left node
    this.nodes[2] = new Quadtree({
      x: x,
      y: y + subHeight,
      width: subWidth,
      height: subHeight
    }, this.max_objects, this.max_levels, nextLevel);

    //bottom right node
    this.nodes[3] = new Quadtree({
      x: x + subWidth,
      y: y + subHeight,
      width: subWidth,
      height: subHeight
    }, this.max_objects, this.max_levels, nextLevel);
  };


  /*
     * Determine the quadtrant for an area in this node
     */
  Quadtree.prototype.getIndex = function (pRect) {
    if (!pRect.collider)
      return -1;
    else {
      var index = -1,
        verticalMidpoint = this.bounds.x + (this.bounds.width / 2),
        horizontalMidpoint = this.bounds.y + (this.bounds.height / 2),

        //pRect can completely fit within the top quadrants
        topQuadrant = (pRect.collider.top() < horizontalMidpoint && pRect.collider.top() + pRect.collider.size().y < horizontalMidpoint),

        //pRect can completely fit within the bottom quadrants
        bottomQuadrant = (pRect.collider.top() > horizontalMidpoint);

      //pRect can completely fit within the left quadrants
      if (pRect.collider.left() < verticalMidpoint && pRect.collider.left() + pRect.collider.size().x < verticalMidpoint) {
        if (topQuadrant) {
          index = 1;
        } else if (bottomQuadrant) {
          index = 2;
        }

        //pRect can completely fit within the right quadrants
      } else if (pRect.collider.left() > verticalMidpoint) {
        if (topQuadrant) {
          index = 0;
        } else if (bottomQuadrant) {
          index = 3;
        }
      }

      return index;
    }
  };


  /*
     * Insert an object into the node. If the node
     * exceeds the capacity, it will split and add all
     * objects to their corresponding subnodes.
     */
  Quadtree.prototype.insert = function (obj) {
    //avoid double insertion
    if (this.objects.indexOf(obj) === -1) {

      var i = 0,
        index;

      //if we have subnodes ...
      if (typeof this.nodes[0] !== 'undefined') {
        index = this.getIndex(obj);

        if (index !== -1) {
          this.nodes[index].insert(obj);
          return;
        }
      }

      this.objects.push(obj);

      if (this.objects.length > this.max_objects && this.level < this.max_levels) {

        //split if we don't already have subnodes
        if (typeof this.nodes[0] === 'undefined') {
          this.split();
        }

        //add all objects to there corresponding subnodes
        while (i < this.objects.length) {

          index = this.getIndex(this.objects[i]);

          if (index !== -1) {
            this.nodes[index].insert(this.objects.splice(i, 1)[0]);
          } else {
            i = i + 1;
          }
        }
      }
    }
  };


  /*
     * Return all objects that could collide with a given area
     */
  Quadtree.prototype.retrieve = function (pRect) {


    var index = this.getIndex(pRect),
      returnObjects = this.objects;

    //if we have subnodes ...
    if (typeof this.nodes[0] !== 'undefined') {

      //if pRect fits into a subnode ..
      if (index !== -1) {
        returnObjects = returnObjects.concat(this.nodes[index].retrieve(pRect));

        //if pRect does not fit into a subnode, check it against all subnodes
      } else {
        for (var i = 0; i < this.nodes.length; i = i + 1) {
          returnObjects = returnObjects.concat(this.nodes[i].retrieve(pRect));
        }
      }
    }

    return returnObjects;
  };

  Quadtree.prototype.retrieveFromGroup = function (pRect, group) {

    var results = [];
    var candidates = this.retrieve(pRect);

    for (var i = 0; i < candidates.length; i++)
      if (group.contains(candidates[i]))
        results.push(candidates[i]);

    return results;
  };

  /*
     * Get all objects stored in the quadtree
     */
  Quadtree.prototype.getAll = function () {

    var objects = this.objects;

    for (var i = 0; i < this.nodes.length; i = i + 1) {
      objects = objects.concat(this.nodes[i].getAll());
    }

    return objects;
  };


  /*
     * Get the node in which a certain object is stored
     */
  Quadtree.prototype.getObjectNode = function (obj) {

    var index;

    //if there are no subnodes, object must be here
    if (!this.nodes.length) {

      return this;

    } else {

      index = this.getIndex(obj);

      //if the object does not fit into a subnode, it must be here
      if (index === -1) {

        return this;

        //if it fits into a subnode, continue deeper search there
      } else {
        var node = this.nodes[index].getObjectNode(obj);
        if (node) return node;
      }
    }

    return false;
  };


  /*
     * Removes a specific object from the quadtree
     * Does not delete empty subnodes. See cleanup-function
     */
  Quadtree.prototype.removeObject = function (obj) {

    var node = this.getObjectNode(obj),
      index = node.objects.indexOf(obj);

    if (index === -1) return false;

    node.objects.splice(index, 1);
  };


  /*
     * Clear the quadtree and delete all objects
     */
  Quadtree.prototype.clear = function () {

    this.objects = [];

    if (!this.nodes.length) return;

    for (var i = 0; i < this.nodes.length; i = i + 1) {

      this.nodes[i].clear();
    }

    this.nodes = [];
  };


  /*
     * Clean up the quadtree
     * Like clear, but objects won't be deleted but re-inserted
     */
  Quadtree.prototype.cleanup = function () {

    var objects = this.getAll();

    this.clear();

    for (var i = 0; i < objects.length; i++) {
      this.insert(objects[i]);
    }
  };



  function updateTree() {
    if (this.quadTree.active) {
      this.quadTree.updateBounds();
      this.quadTree.cleanup();
    }
  }

  //keyboard input
  p5.prototype.registerMethod('pre', p5.prototype.readPresses);

  //automatic sprite update
  p5.prototype.registerMethod('pre', p5.prototype.updateSprites);

  //quadtree update
  p5.prototype.registerMethod('post', updateTree);

  //camera push and pop
  p5.prototype.registerMethod('pre', cameraPush);
  p5.prototype.registerMethod('post', cameraPop);

  //deltaTime
  //p5.prototype.registerMethod('pre', updateDelta);

  /**
   * Log a warning message to the host console, using native `console.warn`
   * if it is available but falling back on `console.log` if not.  If no
   * console is available, this method will fail silently.
   * @method _warn
   * @param {!string} message
   * @private
   */
  p5.prototype._warn = function (message) {
    var console = window.console;

    if (console) {
      if ('function' === typeof console.warn) {
        console.warn(message);
      }
      else if ('function' === typeof console.log) {
        console.log('Warning: ' + message);
      }
    }
  };

}));