Round corners in IE

Question

This demo only Works in IE6, IE7, and IE8.

http://www.impressivewebs.com/css3-rounded-corners-in-internet-explorer/

What technique is being used in this?

Answer 1

They're using an IE conditional comment to load an IE specific stylesheet:

<!--[if gte IE 6.]>
  <link rel="stylesheet" href="http://www.impressivewebs.com/wp-content/themes/iw_2009/ie-stuff.css" type="text/css" media="screen" />
<![endif]-->

This stylesheet defines a style, behaviour, that is applied to the .border-radius div on the demo page (the grey one, with the curvy corners). The stylesheet defines:

.box-radius {
behavior: url(/border-radius.htc);
}

And this url links to the following .htc (Wikipedia article link) file (sort of a dhtml js/vbscript-style scripting language for MS IE):

--Do not remove this if you are using--
Original Author: Remiz Rahnas
Original Author URL: http://www.htmlremix.com
Published date: 2008/09/24

Changes by Nick Fetchak:
- IE8 standards mode compatibility
- VML elements now positioned behind original box rather than inside of it - should be less prone to breakage
Published date : 2009/11/18


<public:attach event="oncontentready" onevent="oncontentready('v08vnSVo78t4JfjH')" />
<script type="text/javascript">

// findPos() borrowed from http://www.quirksmode.org/js/findpos.html
function findPos(obj) {
    var curleft = curtop = 0;

    if (obj.offsetParent) {
        do {
            curleft += obj.offsetLeft;
            curtop += obj.offsetTop;
        } while (obj = obj.offsetParent);
    }

    return({
        'x': curleft,
        'y': curtop
    });
}

function oncontentready(classID) {
  if (this.className.match(classID)) { return(false); }

    if (!document.namespaces.v) { document.namespaces.add("v", "urn:schemas-microsoft-com:vml"); }

    this.className = this.className.concat(' ', classID);
    var arcSize = Math.min(parseInt(this.currentStyle['-moz-border-radius'] ||
                                    this.currentStyle['-webkit-border-radius'] ||
                                    this.currentStyle['border-radius'] ||
                                    this.currentStyle['-khtml-border-radius']) /
                           Math.min(this.offsetWidth, this.offsetHeight), 1);
    var fillColor = this.currentStyle.backgroundColor;
    var fillSrc = this.currentStyle.backgroundImage.replace(/^url\("(.+)"\)$/, '$1');
    var strokeColor = this.currentStyle.borderColor;
    var strokeWeight = parseInt(this.currentStyle.borderWidth);
    var stroked = 'true';
    if (isNaN(strokeWeight)) {
        strokeWeight = 0;
        strokeColor = fillColor;
        stroked = 'false';
    }

    this.style.background = 'transparent';
    this.style.borderColor = 'transparent';

    // Find which element provides position:relative for the target element (default to BODY)
    var el = this;
    var limit = 100, i = 0;
    while ((typeof(el) != 'unknown') && (el.currentStyle.position != 'relative') && (el.tagName != 'BODY')) {
        el = el.parentElement;
        i++;
        if (i >= limit) { return(false); }
    }
    var el_zindex = parseInt(el.currentStyle.zIndex);
    if (isNaN(el_zindex)) { el_zindex = 0; }
    //alert('got tag '+ el.tagName +' with pos '+ el.currentStyle.position);

    var rect_size = {
        'width': this.offsetWidth - strokeWeight,
        'height': this.offsetHeight - strokeWeight
    };
    var el_pos = findPos(el);
    var this_pos = findPos(this);
    this_pos.y = this_pos.y + (0.5 * strokeWeight) - el_pos.y;
    this_pos.x = this_pos.x + (0.5 * strokeWeight) - el_pos.x;

    var rect = document.createElement('v:roundrect');
    rect.arcsize = arcSize +'px';
    rect.strokecolor = strokeColor;
    rect.strokeWeight = strokeWeight +'px';
    rect.stroked = stroked;
    rect.style.display = 'block';
    rect.style.position = 'absolute';
    rect.style.top = this_pos.y +'px';
    rect.style.left = this_pos.x +'px';
    rect.style.width = rect_size.width +'px';
    rect.style.height = rect_size.height +'px';
    rect.style.antialias = true;
    //rect.style.zIndex = el_zindex - 1;

    var fill = document.createElement('v:fill');
    fill.color = fillColor;
    fill.src = fillSrc;
    fill.type = 'tile';

    rect.appendChild(fill);
    el.appendChild(rect);

    var css = el.document.createStyleSheet();
    css.addRule("v\\:roundrect", "behavior: url(#default#VML)");
    css.addRule("v\\:fill", "behavior: url(#default#VML)");

    isIE6 = /msie|MSIE 6/.test(navigator.userAgent);
    // IE6 doesn't support transparent borders, use padding to offset original element
    if (isIE6 && (strokeWeight > 0)) {
        this.style.borderStyle = 'none';
        this.style.paddingTop = parseInt(this.currentStyle.paddingTop || 0) + strokeWeight;
        this.style.paddingBottom = parseInt(this.currentStyle.paddingBottom || 0) + strokeWeight;
    }

    if (typeof(window.rounded_elements) == 'undefined') {
        window.rounded_elements = new Array();

        if (typeof(window.onresize) == 'function') { window.previous_onresize = window.onresize; }
        window.onresize = window_resize;
    }
    this.element.vml = rect;
    window.rounded_elements.push(this.element);
}

function window_resize() {
    if (typeof(window.rounded_elements) == 'undefined') { return(false); }

    for (var i in window.rounded_elements) {
        var el = window.rounded_elements[i];

        var strokeWeight = parseInt(el.currentStyle.borderWidth);
        if (isNaN(strokeWeight)) { strokeWeight = 0; }

        var parent_pos = findPos(el.vml.parentNode);
        var pos = findPos(el);
        pos.y = pos.y + (0.5 * strokeWeight) - parent_pos.y;
        pos.x = pos.x + (0.5 * strokeWeight) - parent_pos.x;

        el.vml.style.top = pos.y +'px';
        el.vml.style.left = pos.x +'px';
    }

    if (typeof(window.previous_onresize) == 'function') { window.previous_onresize(); }
}
</script>

It was an interesting discovery, I haven't seen .htc files used in a while.