200718 Sep Liquid faux columns with background-size

14 Feb

Until the Advanced Layout and Grid Layout modules are implemented, we have to get by with the existing tricks of the trade. One of those is the use of faux columns, a background image which simulates equal-height columns. This is a good technique, but the drawback is that it only works with fixed-width columns.

That problem was overcome with the advent of liquid faux columns, which uses some background-position trickery and a bit of maths to create a variable-width effect.

With the (tentative) introduction of background-size in Safari and Opera, however, faux columns are about to become a lot easier; all you need to do is create a background image and assign a percentage value to background-size, allowing the image to expand or contract with its containing box.

Take a look at this example (only tested in Safari 3 and Opera 9.5; may work in Konqueror 3.5.7 also). If you resize your browser window, the text and columns should maintain their proportions.

The way this is done is with a simple PNG image; I’ve made it 1000px wide, with two coloured columns of 250px each, so that it’s easier to calculate column widths (25%,50%,25%).

I’ve set this as the background-image on the html element, which has been assigned a width of 90%. Inside this there is a container div with a width of 100%, and my three columns with the widths set at the same ratio as the background image:

<div id="container">
	<div id="one">
	</div>
	<div id="two">
	</div>
	<div id="tre">
	</div>
</div>

#container {
position: relative;
width: 100%;
}
#one {
margin: 0 25%;
}
#two, #tre {
position: absolute;
top: 0;
width: 25%;
}
#two { left: 0; }
#tre { right: 0; }

The html element has the background-size declaration applied to it, with a percentage value to make it liquid, using the browser-specific prefixes followed by the proposed declaration (for safety):

html {
background-image: url('opera_bg.png');
-khtml-background-size: 100%;
-o-background-size: 100%;
-webkit-background-size: 90%;
background-size: 100%;
background-position: 50% 0;
background-repeat: repeat-y;
width: 90%;

You’ll notice that the Webkit value is different from the others; during this test, it seems that Webkit obtains its width from the entire browser window, not from the containing element; therefore, we have to set this value to be equal to the width of the containing element. I haven’t tested this thoroughly yet, so I’m not sure if this is a persistent bug or if there’s something I’m doing wrong. Anyway, Opera 9.5 behaves as expected.

After that I’ve added the background-position and background-repeat declarations; background-repeat to tile the image down the page, and background-position because Webkit seems to ignore the margin values and puts the image at top left of the browser window; this is only necessary if you’re centre-aligning your page.

Apart from a little tidying up, that’s it; once the module becomes a recommendation and the browser-specific prefixes are dropped, it will require only a few lines of code for the simple effect. In the meantime, remember that this is for experimentation purposes only and shouldn’t be used in a live environment. This is just a sketch of the technique at the moment, and requires more testing.

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