Util.js

/**
 * Utility functions
 */
PIE.Util = {

    /**
     * To create a VML element, it must be created by a Document which has the VML
     * namespace set. Unfortunately, if you try to add the namespace programatically
     * into the main document, you will get an "Unspecified error" when trying to
     * access document.namespaces before the document is finished loading. To get
     * around this, we create a DocumentFragment, which in IE land is apparently a
     * full-fledged Document. It allows adding namespaces immediately, so we add the
     * namespace there and then have it create the VML element.
     * @param {string} tag The tag name for the VML element
     * @return {Element} The new VML element
     */
    createVmlElement: function( tag ) {
        var vmlPrefix = 'css3vml',
            vmlDoc = PIE._vmlCreatorDoc;
        if( !vmlDoc ) {
            vmlDoc = PIE._vmlCreatorDoc = doc.createDocumentFragment();
            vmlDoc.namespaces.add( vmlPrefix, 'urn:schemas-microsoft-com:vml' );
        }
        return vmlDoc.createElement( vmlPrefix + ':' + tag );
    },


    /**
     * Generate and return a unique ID for a given object. The generated ID is stored
     * as a property of the object for future reuse.
     * @param {Object} obj
     */
    getUID: function( obj ) {
        return obj && obj[ '_pieId' ] || ( obj[ '_pieId' ] = +new Date() + Math.random() );
    },


    /**
     * Simple utility for merging objects
     * @param {Object} obj1 The main object into which all others will be merged
     * @param {...Object} var_args Other objects which will be merged into the first, in order
     */
    merge: function( obj1 ) {
        var i, len, p, objN, args = arguments;
        for( i = 1, len = args.length; i < len; i++ ) {
            objN = args[i];
            for( p in objN ) {
                if( objN.hasOwnProperty( p ) ) {
                    obj1[ p ] = objN[ p ];
                }
            }
        }
        return obj1;
    },


    /**
     * Execute a callback function, passing it the dimensions of a given image once
     * they are known.
     * @param {string} src The source URL of the image
     * @param {function({w:number, h:number})} func The callback function to be called once the image dimensions are known
     * @param {Object} ctx A context object which will be used as the 'this' value within the executed callback function
     */
    withImageSize: function( src, func, ctx ) {
        var sizes = PIE._imgSizes || ( PIE._imgSizes = {} ),
            size = sizes[ src ], img;
        if( size ) {
            func.call( ctx, size );
        } else {
            img = new Image();
            img.onload = function() {
                size = sizes[ src ] = { w: img.width, h: img.height };
                func.call( ctx, size );
                img.onload = null;
            };
            img.src = src;
        }
    }
};