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Re: @font-face and slow downloading

From: John Daggett <jdaggett@mozilla.com>
Date: Mon, 17 Jan 2011 18:13:36 -0800 (PST)
To: Yuzo Fujishima <yuzo@google.com>
Cc: www-style list <www-style@w3.org>
Message-ID: <1845833180.11783.1295316816536.JavaMail.root@cm-mail03.mozilla.org>

Hi Yuzo,

> John and other CSS Font people,
> 
> Can you update me on the status of the standardization for web font
> tentative drawing behavior? What is the ETA?

I think your proposed wording looks fine.  Text display during font
loading should be defined loosely enough to allow UA's flexibility.  But
I would agree that the exact font metrics used should be those of normal
fallback fonts, i.e. the first platform font in the font-family list or
the font that would be used as part of normal system font fallback for a
given set of characters. Using fallback fonts with similar metrics is
actually problematic in practice, font metrics for non-monospace fonts
vary widely and "similar metrics" requires a font explicitly designed to
be similar (e.g. Arial was designed to mimic the metrics of Helvetica).
As others have pointed out, the 'font-size-adjust' property can also
help to some extent.  The spec should include a discussion of this, at
which point we can review the exact wording.

A related issue is some form of event that fires on font loads.  This is
needed for dealing with dynamically font loading and working with
downloadable fonts in <canvas> elements.  An event like this would also
allow more author-level control over visual display during font
downloads.  If folks have ideas/proposals for this that would be good to
discuss.

It's my task to edit the spec and I've been tied up with other tasks for
the past few months.  I hope to work on these edits next month.

John Daggett
 

On Tue, Nov 9, 2010 at 1:31 PM, Yuzo Fujishima <yuzo@google.com> wrote:

    I'd propose that we first agree on
      Q1. whether the tentative drawing behavior is at UA's discretion or not
    and then on
      Q2. how the spec wording should be.

    As to Q1, I think it must be at UA's discretion (rather than document authors').

    Rationale:
    1. Through the discussion so far, it seems to be very difficult to find a
    common ground with that everyone is reasonably happy. Hence mandating
    a behavior doesn't look reasonable.
    2. Allowing authors to control this tentative and transitional behavior
    seems to be an overcommitment for me, especially as a browser developer.

    As to Q2, I'd propose the following, deriving from David's:

    "when a downloadable font is used in a stylesheet, UA may, after waiting for download completion as long as it wants,
    first use the fallback font for rendering as if all downloading have failed and then use the downloadable font
    when the download completes.
    It is recommended to the document author that the fallback font(s) have 'as similar metrics as possible'
    to the downloadable font, so that, if the page is first rendered with a fallback and later with the downloadable font,
    the degree of visual change, re-layout etc., is as small as possible."

    Yuzo

    On Sat, Oct 23, 2010 at 3:50 AM, David Singer <singer@apple.com> wrote:


        On Oct 22, 2010, at 0:22 , Yuzo Fujishima wrote:

        >
        > Hi, David,
        >
        > Sorry if I was unclear.
        >
        > I think the temporary substitute and the permanent fallback should be the same if possible.
        >
        > Put differently, I think the temporary substitute should be the same font as the font that
        > is used when all downloads failed.
        >
        > Yuzo

        Hi, no problem.  We already have syntax for fallback, so we can document that it can also be used as a 'temporary' substitute (with no formal definition of how long temporary can be).

        So, should the specification say that "when a downloaded font is used in a stylesheet, a local fallback font must (should?) also be specified, and that the fallback font may be used by the UA when/while the downloaded font is unavailable.  It is (strongly?) recommended that the fallback font(s) have 'as similar metrics as possible' to the downloaded font, so that, if the page is first rendered with a fallback and later with the downloaded font, the degree of visual change, re-layout etc., is as small as possible."

        David Singer
        Multimedia and Software Standards, Apple Inc.
Received on Tuesday, 18 January 2011 02:14:09 GMT

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