/*** Define an object to hold all our images for the game so images* are only ever created once. This type of object is known as a* singleton.*/
var imageRepository = new function() {// Define imagesthis.background = new Image();// Set images srcthis.background.src = "imgs/bg.png";
}

/*** Creates the Drawable object which will be the base class for* all drawable objects in the game. Sets up default variables* that all child objects will inherit, as well as the default* functions.*/
function Drawable() {this.init = function(x, y) {// Default variablesthis.x = x;this.y = y;}this.speed = 0;this.canvasWidth = 0;this.canvasHeight = 0;// Define abstract function to be implemented in child objectsthis.draw = function() {};
}

/*** Creates the Background object which will become a child of* the Drawable object. The background is drawn on the "background"* canvas and creates the illusion of moving by panning the image.*/
function Background() {this.speed = 1; // Redefine speed of the background for panning// Implement abstract functionthis.draw = function() {// Pan backgroundthis.y += this.speed;this.context.drawImage(imageRepository.background, this.x, this.y);// Draw another image at the top edge of the first imagethis.context.drawImage(imageRepository.background, this.x, this.y - this.canvasHeight);// If the image scrolled off the screen, resetif (this.y >= this.canvasHeight)this.y = 0;};
}
// Set Background to inherit properties from Drawable
Background.prototype = new Drawable();

/*** The animation loop. Calls the requestAnimationFrame shim to* optimize the game loop and draws all game objects. This* function must be a gobal function and cannot be within an* object.*/
function animate() {requestAnimFrame( animate );game.background.draw();
}
/*** requestAnim shim layer by Paul Irish* Finds the first API that works to optimize the animation loop,* otherwise defaults to setTimeout().*/
window.requestAnimFrame = (function(){return  window.requestAnimationFrame   ||window.webkitRequestAnimationFrame ||window.mozRequestAnimationFrame    ||window.oRequestAnimationFrame      ||window.msRequestAnimationFrame     ||function(/* function */ callback, /* DOMElement */ element){window.setTimeout(callback, 1000 / 60);};
})();

/*** Initialize the Game and starts it.*/
var game = new Game();
function init() {if(game.init())game.start();
}