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Re: [css-text][css-fonts][proposal] font-side-bearings: normal | trimmed

From: Peter Moulder <pjrm@mail.internode.on.net>
Date: Mon, 20 Jan 2014 19:48:40 +1100
To: www-style@w3.org
Message-ID: <20140120084840.GA4498@mail.internode.on.net>
On Sat, Jan 18, 2014 at 10:41:01AM +0100, François REMY wrote:

> Just for the record, I would like to propose a new property called “font-side-bearings” and which could take the values “normal” and “trimmed”, where “normal” would be the default. The goal of the property is to make sure the first glyph of a line is blackbox-aligned and not moved towards right a bit by the left bearing (in a ltr flow).
> Context:
>  http://msdn.microsoft.com/en-us/library/windows/apps/windows.ui.xaml.opticalmarginalignment.aspx
> Thoughts?

A few random thoughts:

  - An option for such a feature is to express it in terms of the general
    effect (usually called margin kerning or optical margins) rather than
    necessarily require a specific calculation.

  - The OpenType 'opbd' table (and associated 'lfbd' and 'rtbd' tables) are

  - The css-fonts 'font-kerning' property is relevant.

  - Implementations don't need a property to implement this: font rendering
    (including kerning) is up to implementations.

  - The mechanism given in the web page is rather simplistic.

  - A property might limit the harms of a simplistic approach.

  - If margin kerning adjustments are to be synthesized (e.g. as described
    in that web page), then some things to be careful of are preformatted
    content, spacing characters, and wide combining marks.

  - Last I looked (a couple of years ago), kerning (including margin
    kerning) isn't yet well understood, or at least not publicly described.
    So even if there's a property value that specifies a particular method
    (as might be useful for predictability among UAs), there should also
    be an 'auto' value that allows UAs to do better, as the state of the
    art improves.

Received on Monday, 20 January 2014 08:49:02 UTC

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