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Re: [css-text] Shaping Isolation and Layout Separation of Inlines

From: fantasai <fantasai.lists@inkedblade.net>
Date: Mon, 18 Aug 2014 11:34:12 -0700
Message-ID: <53F24724.7020601@inkedblade.net>
To: John Daggett <jdaggett@mozilla.com>
CC: WWW International <www-international@w3.org>, www-style@w3.org
On 08/14/2014 09:00 PM, John Daggett wrote:
> fantasai wrote:
>
>> Shaping is not broken across an inline element boundary unless:
>>
>>     1. one of margin/border/padding are non-zero
>>
>>     2. vertical-align is not 'baseline'
>>
>>     3. it is a bidi isolation boundary
>>
>> Note: This means that color changes, font changes, letterspacing
>> changes, etc. have no effect on shaping. Shaping might not result
>> in the glyphs joining correctly, but will nonetheless choose the
>> correct form of the letter (initial, medial, final, isolated).
>
> Shaping by definition is the mapping of text to a set of associated
> glyphs and positions. So font changes having no effect on shaping
> is a non-sequitur. Any property that affects the set of features
> applied to a given text run is an input to shaping, so changes in
> those may affect shaping results.

For Arabic shaping, it's a bit more straightforward (at the conceptual
level, not the font level maybe). There are four basic "shapes" per
letter, and the appropriate "shape" can be determined by character
analysis, independent of glyphs. (The font engine might have multiple
glyphs per shape, of course, and you can't determine which of those
to use by character analysis.)

> Not sure what the intended purpose of this text is but I guess the
> first question is whether it's necessary or not.

We got requests to clarify when Arabic joining is broken or not
broken at an inline boundary. For example, some implementations
breaking joining even when there's no style change. This is
clearly bad. As another example, in another implementation
joining was preserved even when margin/border/padding was nonzero,
which created problems for a set of inlined list items that were
now pretending to be all part of the same word.

~fantasai
Received on Monday, 18 August 2014 18:34:43 UTC

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