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Blink started supporting font-size-adjust css property

Posted on 26/03/2015 by ChangSeok Oh

Hi there. I’m back relatively early with an up-to-date news!

Tl;Dr; The font-size-adjust css property is available in blink nightly build. You should be able to try it in the next release by enabling experimental web platform features in chrome://flags.

You might not know the property or be not that interested in it if you are a CJK(Chinese, Japanese or Korean) user. But I believe this is quite convenient for alphabetic language users. Let me elaborate on it a little bit, what it is and how to use it.

The font-size-adjust is an established css spec. It adjusts font-size as the name is. (Here the font-size means the font-size css property.) Then what are differences from the font-size? Well, font-size-adjust doesn’t specify an font size explicitly, instead it does specify a relative size value(we call it ‘aspect value’) for alternative fonts.

Content authors naturally want to build and keep their web site as beautifully as they can. But at the point, one evitable problem raises. It’s font.
Font is a long term headache for web designers. Because some of fonts are not free so that designers should resolve license issues before using any fonts. Even though they have an authority to use any beautiful font, it might be a dangerous assumption that fonts were installed or available in all end-user’s systems. Status of supporting any fonts is quite different from each platforms. @font-face solved this problem, but there are some browsers not supporting it yet. For those reasons(may not), content authors tend to use a system default font or list preferred fonts to font-family in order like below.

p { font-family: Verdana, Futura, Times; }

Verdana, Futura and Times are popular and gorgeous. However here is an another problem. Legibility.
You might be already experienced that fonts look differently sized even though you specified a same value for font-size.

same font size but look differently sized

As you can see above, Verdana looks bigger than Times with same 10px font size. This is because Verdana has bigger x-height over Times. In other words, any font getting big x-height looks relatively bigger and more clear. Here we can define the relative x-height size over font-size as aspect value. (i, e. x-height / font-size) The font-size-adjust defines this aspect value. Especially you set an aspect value of the first font listed in font-family to font-size-adjust so that you can keep actual font size of other alternative fonts and keep same legibility among different fonts.

font-size-adjust works like this

Firefox has been supporting font-size-adjust for a long time, but Blink & WebKit haven’t. I had given efforts on the css property for a while on blink first, all relevant patch set finally landed few days ago. My first trial to get involved in blink project was not that successful though, this went smoothly in overall. I’m very happy with it. Next step will be bringing this into WebKit as well. It should be done with not much of work I think.

I wish content authors to feel happy with the new font related property and their lives to go easier than ever. Finally, I should thank Collabora Ltd. for making this happen as usual.

Followings are all relevant discussions and patches happened while working in progress.

Spec :
http://dev.w3.org/csswg/css-fonts/#font-size-adjust-prop
Discussions :
https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/lqd_g6Z6fH4
https://lists.w3.org/Archives/Public/www-style/2015Mar/0282.html
Patch set :
https://codereview.chromium.org/943463002
https://codereview.chromium.org/983073002
https://codereview.chromium.org/1024473004
https://codereview.chromium.org/1028943002

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