Thursday, September 10, 2009

MoocanvasShadow reviewed - shadows for everyone

Hi all,
well, this time I'd like to write about a nice class implemented using mootools libraries used to paint shadows around blocks. His name is mooCanvasShadow, written by Arian Stolwijk, and here the link to the project. This class uses the mooCanvas class of ibolmo's.
When I used this class for some projects I encountered some difficulties and some strange behavioures, so I tried to reniew this class which was shared under the MIT license. There was a problem when applying a shadow to a container div which was centered in the page when resizing the browser window. The problem was that while resizing the browser window the container centered is moved in order to keep the centered position, but the canvas area painted in order to get the shadow was static and positioned absolute relative to the body, so couldn't follow the container in motion. The solution is to paint the canvas area relative to the container we want to apply shadows to (changes made to the method createCanvasDiv). This way if it moves than the canvas follows it.
Another adjustment was made in a regular expression matching colors, it didn't consider not capital letters and so always put the default color if you write colors codes this way: #ffffff (like me).
Above the major things, now the code:

//AbiCanvasShadow, Mootools Canvas Dropshadow Abidibo extended
Script: CanvasShadow.js
    Contains the Canvas class.
    MooTools, <http:"">
        Element, and its dependencies
    MooCanvas, <http:"" moocanvas="" projects="">
    Arian Stolwijk, <http:"">
Adjusted by
    Abidibo, <http:"">
    MIT License, <http:"" mit_license="" wiki="">

var AbiCanvasShadow = new Class({
     * This function creates a new canvas element of MooCanvas
     * The elements will be placed at the right position, so the
     * canvas element is right behind the to-shadow element
     * @param {Object} shadowDiv this div will get a shadow
     * @param {Object} options the options:
     *         size: The size of the shadow
     *         radius: the radius of the shadow corners
     *         opacity: The opacity of the shadow
     *         color: The shadow color, this should be like #FF9900,
     *             or an array with the rgb colors [255,0,255]
     *         overwrite: if the canvas element already exists,
     *             it wil dispose that element and create a new one
    initialize: function(shadowDiv,options){        
        // Set shadow div
        this.shadowDiv = shadowDiv;
        // Get the coordinates of the element
        this.position = shadowDiv.getCoordinates();
        // Set some options
        this.size = options.size;
        var radius = options.radius;
        var opacity = options.opacity;
        if($(shadowDiv.get('id')) == false){
        // Dispose the already existing element, if needed
        if ($type(options.overwrite) == 'boolean' &amp;&amp; options.overwrite == true) {
            if ($type($(shadowDiv.get('id') + '_mooShadow')) == 'element') {
                $(shadowDiv.get('id') + '_mooShadow').dispose();

        // Create a new Canvas object, of MooCanvas
        this.canvas = new Canvas({
            'width': this.position.width + (this.size * 2),
            'height': this.position.height + (this.size * 2),
            'id': shadowDiv.get('id')+'_mooShadow'
        // Create a div and put the canvas element in it to set it at the right position

        // Create the context
        var ctx = this.canvas.getContext("2d");
        // Create the shadow color
            options.color = options.color.hexToRgb(true);
        if($type(options.color) == 'array' &amp;&amp; $type(options.color[2]) != 'undefined'){
            var color = options.color[0]+','+options.color[1]+','+options.color[2];    
            var color = '0,0,0';

        // Create the retangles/ the actual shadow
        for (var i = this.size; i &gt;= 0; i--) {
            ctx.fillStyle = "rgba("+color+", "+opacity/(this.size-i)+")";

     * This function creates a div where the canvas element is in inserted
     * This element will position behind the to-shadow div
    createCanvasDiv: function(){
        this.canvasDiv = new Element('div',{
                'width': this.position.width+(this.size*2),
                'height': this.position.height+(this.size*2),
                'z-index': -1,
                'position': 'absolute',
                'left': '-'+this.size+'px',
                'top':  '-'+this.size+'px'
     * This method creates a rounded rectangle
     * @param {Object} ctx the canvas context
     * @param {Object} x the upper left x-axis position
     * @param {Object} y the upper left y-axis positoin
     * @param {Object} width the retangle width
     * @param {Object} height the retangle height
     * @param {Object} radius the corner radius
    roundedRect: function (ctx,x,y,width,height,radius){

     * This method set an random ID to an element
     * @param {Object} div
    giveId: function(div){

 * @param {Object} options: the same options as the mooCanvasShadow() class
    AbiCanvasShadow: function (options){
        new AbiCanvasShadow(this,options);        
        return this;

and how to use it:

    // 'mainContainer' is the ID of the element
        opacity: 0.2,
        size: 14,
        radius: 10,
        color: '#333333'

The html structure must be this way:

<div id="mainContainer">
     <div id="container">   
     your site, your content

that because of... guess it?   IE. Si seƱores, another self behaviour for IE7 and IE6 and I don't know if IE8 too. Whit these horrible browsers using only one container causes the below canvas area to affect the background of the element even if a color was setted. So some points:
  • Use two container and apply the effect to the outer
  • Very important: set the position property of mainContainer as relative, that because the canvas is positioned absolute relative to it
  • Set the width of 'mainContainer' equal to the width of 'container'
  • Set a background color for 'container'
  • Pay attention if using padding or margins, that is properties affecting the position of the element 
Last thing. You may see that I've setted a delay of 800 ms to the function called at the event domready. This value may be 0 or higher, it depends. It is useful because with FF there's a different behaviour in applyng css styles when recharging a page or get it through a link. When recharging a page the css seems to be applied a bit later, that causes for example that an horizontal menu may be displayed for a while in his "<ul><li>" form (vertically), and after rendered in horizontal, saving space. But if the coordinates of the element are taken in the instant the menu is higher then the canvas is painted with these values. After the menu becomes horizontal, saves vertical space and then the dimension of the element and his shadows are different. Using this delay this problem is prevented. Another way could be to call the function not at the event 'domready' but at the event onload, that is:
window.onload = function ()...
but in this case the interval between the appearence of the element and its shadow is grater, especially if the element contains iframe or heavy elements.
That's all guys, hasta la proxima!

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