1     /**
2         A manager for all the objects in the game
3         @author <a href="mailto:matthewcasperson@gmail.com">Matthew Casperson</a>
4         @class
5     */
6     function GameObjectManager()
7     {
8         /** An array of game objects 
9             @type Arary
10        */
11        this.gameObjects = new Array();
12        /** The time that the last frame was rendered  
13            @type Date
14        */
15        this.lastFrame = new Date().getTime();
16        /** The global scrolling value of the x axis  
17            @type Number
18        */
19        this.xScroll = 0;
20        /** The global scrolling value of the y axis  
21            @type Number
22        */
23        this.yScroll = 0;
24        /** A reference to the ApplicationManager instance  
25            @type ApplicationManager
26        */
27        this.applicationManager = null;
28        /** A reference to the canvas element  
29            @type HTMLCanvasElement
30        */
31        this.canvas = null;
32        /** A reference to the 2D context of the canvas element
33            @type CanvasRenderingContext2D
34        */
35        this.context2D = null;
36        /** A reference to the in-memory canvas used as a back buffer 
37            @type HTMLCanvasElement
38        */
39        this.backBuffer = null;
40        /** A reference to the backbuffer 2D context 
41            @type CanvasRenderingContext2D
42        */
43        this.backBufferContext2D = null;
44
45        /**
46            Initialises this object
47            @return A reference to the initialised object
48        */
49        this.startupGameObjectManager = function()
50        {
51            // set the global pointer to reference this object
52            g_GameObjectManager = this;
53
54            // get references to the canvas elements and their 2D contexts
55            this.canvas = document.getElementById('canvas');
56            this.context2D = this.canvas.getContext('2d');
57            this.backBuffer = document.createElement('canvas');
58            this.backBuffer.width = this.canvas.width;
59            this.backBuffer.height = this.canvas.height;
60            this.backBufferContext2D = this.backBuffer.getContext('2d');
61
62            // create a new ApplicationManager
63            this.applicationManager = new ApplicationManager().startupApplicationManager();
64
65            // use setInterval to call the draw function 
66            setInterval(function(){g_GameObjectManager.draw();}, SECONDS_BETWEEN_FRAMES);
67
68            return this;
69        }
70
71        /**
72            The render loop
73        */
74        this.draw = function ()
75        {
76            // calculate the time since the last frame
77            var thisFrame = new Date().getTime();
78            var dt = (thisFrame - this.lastFrame)/1000;
79            this.lastFrame = thisFrame;
80
81            // clear the drawing contexts
82            this.backBufferContext2D.clearRect(0, 0, this.backBuffer.width, this.backBuffer.height);
83            this.context2D.clearRect(0, 0, this.canvas.width, this.canvas.height);
84
85            // first update all the game objects
86            for (x in this.gameObjects)
87            {
88                if (this.gameObjects[x].update)
89                {
90                    this.gameObjects[x].update(dt, this.backBufferContext2D, this.xScroll, this.yScroll);
91                }
92            }
93
94            // then draw the game objects
95            for (x in this.gameObjects)
96            {
97                if (this.gameObjects[x].draw)
98                {
99                    this.gameObjects[x].draw(dt, this.backBufferContext2D, this.xScroll, this.yScroll);
100               }
101           }
102
103           // copy the back buffer to the displayed canvas
104           this.context2D.drawImage(this.backBuffer, 0, 0);
105       };
106
107       /**
108           Adds a new GameObject to the gameObjects collection
109           @param gameObject The object to add
110       */
111       this.addGameObject = function(gameObject)
112       {
113           this.gameObjects.push(gameObject);
114           this.gameObjects.sort(function(a,b){return a.zOrder - b.zOrder;})
115       };
116
117       /**
118           Removes a GameObject from the gameObjects collection
119           @param gameObject The object to remove
120       */
121       this.removeGameObject = function(gameObject)
122       {
123           this.gameObjects.removeObject(gameObject);
124       }
125   }