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CSS3 Web Fonts issue with ‘block on download’

From: Oli Studholme <w3-style@boblet.net>
Date: Thu, 7 May 2009 20:26:34 +0900
Message-ID: <a015dab70905070426s7b4660f9xd3df664cdccf9a23@mail.gmail.com>
To: www-style@w3.org
Hi All,

I recently came across an issue when an @font-face takes a long time
to download (eg large font, slow server etc). In the font-matching
algorithm the CSS3 Web Fonts working draft says:
4.4 “The UA may choose to block on this download or may choose to
proceed to the next step while the font downloads.”

Firefox implements this by proceeding with the font matching algorithm
while the @font-face downloads. This results in the content being
drawn quickly, with a redraw once the @font-face font has downloaded.
Safari implements this by ‘blocking on download’ (I’m guessing that
means ‘stop the text layout algorithm until @font-face finishes
downloading’), which if the @font-family font takes a long time to
download can mean the user sees what appears to be a broken page. This
is especially noticeable if the font is used for body text. This has
led to the following Webkit bug:
which contains this demonstration:

While requiring a redraw has visual and performance drawbacks, I think
permitting nothing to be displayed until a font downloads presents a
serious usability issue, especially for people accessing pages with
large double-byte fonts or over slow connections. I humbly submit this
sentence should be changed to “The UA must proceed to the next step
while the font downloads.”

Thank you for your time

peace - oli studholme
Received on Thursday, 7 May 2009 11:29:24 UTC

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