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

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Fri, 15 Aug 2014 10:09:49 -0700
Message-ID: <CAAWBYDALF6f7tCRbc3ocZuZmD_gvMYquSky=mYjU3X2MnUNxLA@mail.gmail.com>
To: John Daggett <jdaggett@mozilla.com>
Cc: fantasai <fantasai.lists@inkedblade.net>, WWW International <www-international@w3.org>, www-style list <www-style@w3.org>
On Thu, Aug 14, 2014 at 9:00 PM, John Daggett <jdaggett@mozilla.com> 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.
>
> I think in practice the complexities of text handling at this level make it very difficult to come up with easy generalizations like this. Not sure what the intended purpose of this text is but I guess the first question is whether it's necessary or not.

You're right about full shaping across a word (thus the note about
"shaping might not result in the glyphs joining correctly"), but
per-character shaping (selecting the initial/medial/final/isolated
form) is necessary for remotely correct rendering, and can happen
regardless of what changes occur from one character to the next.

~TJ
Received on Friday, 15 August 2014 17:10:37 UTC

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