source: extensions/GDThumb/js/image.loader.js @ 31946

function ImageLoader(opts) {
        this.opts = jQuery.extend( {
                        maxRequests: 6,
                        onChanged: jQuery.noop
                }, opts||{} );
}

ImageLoader.prototype = {
        loaded: 0,
        errors: 0,
        errorEma: 0,

        pause: false,

        current: [],
        queue: [],
        pool: [],

        remaining: function() {
                return this.current.length + this.queue.length;
        },

        add: function(urls) {
                this.queue = this.queue.concat( urls );
                this._fireChanged("add");
                this._checkQueue();
        },

        clear: function() {
                this.queue.length = 0;
                while (this.current.length)
                        jQuery( this.current.pop() ).unbind();
                this.loaded = this.errors = this.errorEma = 0;
        },

        pause: function(val) {
                if (val !== undefined)
                {
                        this.paused = val;
                        this._checkQueue();
                }
                return this.paused;
        },

        _checkQueue: function() {
                while (!this.paused
                        && this.queue.length
                        && this.current.length < this.opts.maxRequests)
                {
                        this._processOne( this.queue.shift() );
                }
        },

        _processOne: function(url) {
                var img = this.pool.shift() || new Image;
                this.current.push(img);
                var that = this;
                jQuery(img).bind( "load error abort", function(e) {
                //img.onload = function(e) {
                        jQuery(img).unbind();
                        img.onload=null;
                        that.current.splice(jQuery.inArray(img, that.current), 1);
                        if (e.type==="load") {
                                that.loaded++;
                                that.errorEma *= 0.9;
                        }
                        else {
                                that.errors++;
                                that.errorEma++;
                                if (that.errorEma>=20 && that.errorEma<21)
                                        that.paused = true;
                        }
                        that._fireChanged(e.type, img);
                        that._checkQueue();
                        that.pool.push(img);
                } );
                img.src = url;
        },

        _fireChanged: function(type, img) {
                this.opts.onChanged(type, img);
        }
}