Re: [css3-fonts][css-text-decor] Decorating superscripts/subscripts

Le Lun 13 mai 2013 22:32, "Gérard Talbot" a écrit :
>
> Le Lun 13 mai 2013 22:04, John Daggett a écrit :
>>
>>
>> fantasai wrote:
>>
>>> The CSS3 Fonts module offers a 'font-variant-position' property as
>>> an improved substitute for superscripts and subscripts. The goal is,
>>> I hope, that going forward, authors would use this mechanism to
>>> produce "real" superscripts and subscripts, using correctly-adjusted
>>> glyphs from the font rather than manually synthesizing them by means
>>> of 'vertical-align' and 'font-size' adjustments.
>>
>> This 'font-variant-position' property [1] is not a replacement for the
>> existing subscript/superscript mechanism in HTML which uses a
>> combination of 'font-size'
>
> Most browsers use in their user agent style sheet:
>
> sub, sup {font-size: smaller;}
> /* though Appendix D gives small, sub, sup {font-size: .83em} */
>
>> and 'vertical-align' to render elements in
>> superscripts and subscripts.
>>
>> We discussed this in great detail in the past and actually resolved on
>> this at the Hamburg F2F [2]:
>>
>>> - RESOLVED: the 'font-variant-position' property is defined independent
>>>             of the existing use of the font-size/vertical-align
>>> properties
>>>             to synthesize subscripts/superscripts
>>
>> The use of variant glyphs for superscripts and subscripts doesn't
>> allow for nested superscripts and subscripts, nor does it allow for
>> images or other elements included in the superscript or subscript
>> content.  It's use is limited to simple, typographic superscripts and
>> subscripts that match the surrounding text.
>>
>>> There's a problem with this however, which is that, since it's now
>>> just done by glyph substitution, the text-decoration code doesn't
>>> know about it, and can't draw underlines, strike-throughs, or
>>> overlines correctly.
>>
>> I think you're misrepresenting "correct" behavior here.  If an author
>> underlines a section of text containing a superscript or subscript and
>> uses 'font-variant-position' to choose the appropriate variant glyphs,
>> the text will display close to the way it does today (modulo Webkit
>> text-decoration bugs):
>>
>> Testcase:
>> http://people.mozilla.org/~jdaggett/tests/superscript-underline.html
>>
>
>
> In several places in that superscript-underline.html test page, the text
> in that webpage uses/says "superscript" when in fact it should be
> using/saying "subscript".
>
> eg.
>
> "
> Below is a comparison of underlining of superscripts using the HTML <sup>
> element
> "
>
> should be instead
>
> "
> Below is a comparison of underlining of subscripts using the HTML <sub>
> element
> "
>
> and
>
> "
> if the text decoration is only applied to the superscript,
> "
>
> should be instead
>
> "
> if the text decoration is only applied to the subscript,
> "
>

John,

please forget the above. I have a small monitor screen and I didn't see
the end of the lines when making those comments. Now, I see the
superscript 5.

Sorry about that.

Gérard

>
> We created several tests in bugzilla bug report (starting from comment #7)
> https://bugzilla.mozilla.org/show_bug.cgi?id=695442#c7
>
>
>> Rendering in Firefox on OSX:
>> http://lists.w3.org/Archives/Public/www-archive/2013May/att-0025/superscript-underline.png
>>
>> If an author wants to underline *just* the content in the superscript
>> or subscript span, the baseline for the variant glyphs is the same as
>> the surrounding text and the underline will appear at the same place
>> it does for surrounding text.  The same is true Unicode
>> superscript/subscript codepoints (U+2070:209C), they are treated as
>> glyphs with the same baseline as surrounding text (see Wikipedia for a
>> list of these [3]).  This is just a limitation of using variant
>> glyphs.
>>
>>> So, somehow, we need to have a concept of the synthesized text's
>>> size and baseline, and be keying the decorations off of that.
>>
>> We discussed why this isn't possible at the Hamburg F2F last year.  As
>> John Hudson was gracious enough to point out again, there aren't
>> really reliable metrics that can be used to infer the baseline of
>> variant superscript/subscript glyphs.
>
> John, I really have to ask you this: which software do you use for
> gathering typography metrics of TTF fonts under Linux (debian
> distributions like Kubuntu)?
>
> This is something I've been looking for for months now..
>
>
>
>
> Under Windows, I use ttfdump:
>
> ttfdump filename -tOS/2 -nx -h
>
> ttfdump AHEM____.TTF -tOS/2 -nx -h
>
> ; TrueType v1.0 Dump Program - v1.8, Oct 29 2002, rrt, dra, gch, ddb, lcp,
> pml
> ; Copyright (C) 1991 ZSoft Corporation. All rights reserved.
> ; Portions Copyright (C) 1991-2001 Microsoft Corporation. All rights
> reserved.
>
> Gérard
>
>> I posted a discussion of this
>> with examples [4] and at the F2F meeting we discussed these:
>>
>> Comparing synthesized superscripts/subscripts to variants
>> http://people.mozilla.org/~jdaggett/tests/subsupermetrics.png
>>
>> If an author wants to use subscripts and superscripts that best match
>> the surrounding content, the use of variant glyphs is ideal.  However,
>> if they want complicated presentation behavior then the existing model
>> of using font-size/vertical-align is a better choice.  For example, in
>> the Wikipedia case where superscripts are contained in square brackets
>> (e.g. [2]) and hovering over the link shows an underline, the existing
>> HTML model is a better choice, since most fonts don't provide
>> superscript variant glyphs for the square brackets anyways.
>>
>> This feature addresses the needs of a specific, common set of use
>> cases.  I don't think we need to try and unify it with the approach
>> used in the past and the wording in the spec reflects that.
>>
>> Regards,
>>
>> John Daggett
>>
>> [1] font-variant-position
>> http://dev.w3.org/csswg/css-fonts/#font-variant-position-prop
>>
>> [2] Hamburg F2F discussion of superscript/subscript feature
>> http://lists.w3.org/Archives/Public/www-style/2012May/0530.html
>>
>> [3] Wikipedia page on superscript/subscript variant codepoints in
>> Unicode
>> http://en.wikipedia.org/wiki/Unicode_subscripts_and_superscripts
>>
>> [4] discussion of differences between variant glyphs and HTML
>> http://lists.w3.org/Archives/Public/www-style/2012May/0369.html
>>
>>
>>
>
>
> --
> CSS 2.1 Test suite RC6, March 23rd 2011
> http://test.csswg.org/suites/css2.1/20110323/html4/toc.html
>
> Contributions to CSS 2.1 test suite
> http://www.gtalbot.org/BrowserBugsSection/css21testsuite/
>
> Web authors' contributions to CSS 2.1 test suite
> http://www.gtalbot.org/BrowserBugsSection/css21testsuite/web-authors-contributions-css21-testsuite.html
>
>
>


-- 
CSS 2.1 Test suite RC6, March 23rd 2011
http://test.csswg.org/suites/css2.1/20110323/html4/toc.html

Contributions to CSS 2.1 test suite
http://www.gtalbot.org/BrowserBugsSection/css21testsuite/

Web authors' contributions to CSS 2.1 test suite
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Received on Tuesday, 14 May 2013 02:51:12 UTC