PC World Komputer 2010 April/PCWorld0410.iso/pluginy Firefox/8614/8614.xpi/chrome/extension.jar/content/utils/ImageLoader.js

JavaScript | 2010-02-10 | 4.8 KB | 163 lines

Glydo.PrioritizedImageLoader = Prototype.Class.create(Glydo.EventSource,{

    initialize: function($super,sources_to_try,prefetch,options) {
        $super();
        this.options = options || {};
        this.sources = sources_to_try;
        this.fetch = prefetch;
        this.waiting = false;
        this.startPrefetch();
    },

    startPrefetch: function() {
        this.cancelled = false;
        this.next = 0;
        this.succeeded = false;
        this.failed = false;
        this.tryNextImage();
    },

    completeFetch: function() {
        this.fetch = null;
        if (!this.done) {
            this.tryNextImage();
        }
    },

    get done() {
        return this.succeeded || this.failed;
    },

    cancel: function() {
        this.cancelled = true;
        if (this.loader) {
            this.loader.src = null;
            delete this.loader;
        }
        this.next = 0;
    },

    tryNextImage: function() {
        if (this.cancelled) {
            return;
        }
        if (this.waiting) {
            return;
        }

        if (this.next >= this.sources.length) {
            this.failed = true;
            this.fire('onImageLoadingFailure',this);
            return;
        }

        if ((this.fetch !== null) && this.next >= this.fetch) {
            return;
        }


        var loader = new Image();

        var me = this;
        loader.onload  = Prototype.F.bind(this.onLoadSuccess,this);
        loader.onerror = Prototype.F.bind(this.onLoadError,this);
        loader.onabort = Prototype.F.bind(this.onLoadError,this);

        this.loader = loader;
        this.cur = this.sources[this.next++];
        if (typeof(this.cur) == "string") {
            loader.src = this.cur;
        } else {
            loader.src = this.cur.url;
        }
        this.waiting = true;
    },

    onLoadError: function()    {
        delete this.loader;
        this.waiting = false;
        this.tryNextImage();
    },

    onLoadSuccess: function() {
        this.waiting = false;
        if (this.cancelled) {
            return;
        }
        if (this.cur.validation && Prototype.O.isFunction(this.cur.validation)) {
            if (!this.cur.validation.call(this.cur,this.loader)) {
                this.onLoadError();
                return;
            }
        }
        if (this.options.validation && Prototype.O.isFunction(this.options.validation)) {
            if (!this.options.validation.call(this.cur,this.loader)) {
                this.onLoadError();
                return;
            }
        }
        this.image = this.loader;
        this.succeeded = true;
        this.fire('onImageLoadingSuccess',this);
    },
});


Glydo.BestThumbnailLoader = Prototype.Class.create(Glydo.PrioritizedImageLoader,{
    initialize: function($super,targetWidth, targetHeight,thumbnailGroups,options) {
        this.targetWidth = targetWidth;
        this.targetHeight = targetHeight;
        this.thumbnailGroups = thumbnailGroups;
        var thumbnails_to_try =
            this.thumbnailGroups.map(this.prioritizeThumbnails,this).reduce(
                function (a,b) { return a.concat(b); },[]);
        var prefetch = null;
        for (var i = 0; i < thumbnails_to_try.length; ++i) {
            if (thumbnails_to_try[i].lazy) {
                prefetch = i;
            }
        }
        thumbnails_to_try = Prototype.A.pluck(thumbnails_to_try,"thumbnail");
        $super(thumbnails_to_try,prefetch,options);
    },

    prioritizeThumbnails: function(thumbnails) {
        var thumbnailsWithPenalties = thumbnails.map(
            function (thumbnail) {
                var xFactor = this.targetWidth / thumbnail.width;
                var yFactor = this.targetHeight / thumbnail.height;
                var factor = Math.max(Math.min(xFactor,yFactor,Glydo.BestThumbnailLoader.Consts.MAX_THUMBNAIL_SCALING_FACTOR),Glydo.BestThumbnailLoader.Consts.MIN_THUMBNAIL_SCALING_FACTOR);
                var resultWidth = factor * thumbnail.width;
                var resultHeight = factor * thumbnail.height;
                var overflowArea = 0;
                var underfillArea = 0;
                if (resultWidth > this.targetWidth) {
                    overflowArea += (resultWidth - this.targetWidth) * resultHeight;
                } else {
                    underfillArea += (this.targetWidth - resultWidth) * this.targetHeight;
                }
                if (resultHeight > this.targetHeight) {
                    overflowArea += (resultHeight - this.targetHeight) * Math.min(resultWidth,this.targetWidth);
                } else {
                    underfillArea += (this.targetHeight - resultHeight) * Math.min(resultWidth,this.targetWidth);
                }
                var areaPenalty = (
                        Glydo.BestThumbnailLoader.Consts.THUMBNAIL_UNDERFILL_PENALTY*underfillArea +
                        Glydo.BestThumbnailLoader.Consts.THUMBNAIL_OVERFLOW_PENALTY*overflowArea) / (this.targetWidth * this.targetHeight);
                var factorPenalty = (factor > 1 ?
                        Math.log(factor) / Math.log(Glydo.BestThumbnailLoader.Consts.MAX_THUMBNAIL_SCALING_FACTOR) :
                        Math.log(factor) / Math.log(Glydo.BestThumbnailLoader.Consts.MIN_THUMBNAIL_SCALING_FACTOR));
                var penalty = areaPenalty + factorPenalty;
                return ({ penalty: penalty, thumbnail: thumbnail, lazy: !!thumbnail.lazy});
            },this);
        return thumbnailsWithPenalties.sort(function(a,b) { return a.penalty - b.penalty; });
    },
});

Glydo.BestThumbnailLoader.Consts = {
        MAX_THUMBNAIL_SCALING_FACTOR: 1.1,
        MIN_THUMBNAIL_SCALING_FACTOR: 0.1,
        THUMBNAIL_UNDERFILL_PENALTY: 3.0,
        THUMBNAIL_OVERFLOW_PENALTY: 1.0,
};