Basic Game Objects - Building JavaScript Games for Phones, Tablets, and Desktop - page 89

the sprite-loading code, you simply have to include the source file containing the code into your new
game application, instead of sorting through the Painter game code to find what you need. Another
reason to do this is to enable you to more quickly create similar games later. You might find yourself
developing a game that is similar to a game you developed earlier. By organizing code in this way,
you can produce your new game more rapidly while also not reinventing the wheel.
The Painter4 example creates a separate Game.js file that contains the Game object and a number
of useful methods belonging to that object. The parts that are specific to Painter have been moved
to the Painter.js file. In that file, you have a method for loading sprites as well as a method for
initializing the game. Furthermore, a new file called PainterGameWorld.js handles the various objects
in the game. In the previous versions of Painter, this game world consisted only of a background
image and a cannon. In the next section, you add a ball to this game world. The Painter game world
is then defined by an object that makes sure all the game objects are updated and drawn. This is
part of the definition of the painterGameWorld object:
var painterGameWorld = {
};
painterGameWorld.handleInput = function (delta) {
ball.handleInput(delta);
cannon.handleInput(delta);
};
painterGameWorld.update = function (delta) {
ball.update(delta);
cannon.update(delta);
};
painterGameWorld.draw = function () {
Canvas2D.drawImage(sprites.background, { x : 0, y : 0 }, 0,
{ x : 0, y : 0 });
ball.draw();
cannon.draw();
};
When you initialize the game, you initialize the game objects, and you tell the Game object that the
object governing the game world is painterGameWorld , as follows:
Game.initialize = function () {
cannon.initialize();
ball.initialize();
Game.gameWorld = painterGameWorld;
};
Inside the Game.mainLoop method, you now only have to make sure to call the right methods on the
gameWorld variable (which refers to painterGameWorld ):
Game.mainLoop = function () {
Game.gameWorld.handleInput();
Game.gameWorld.update();
Canvas2D.clear();