bugFree UCS Outline Fonts - Bugs: bug #52571, Superscripts and subscripts do not...


bug #52571: Superscripts and subscripts do not work in all scripts

Submitted by:  David Corbett <dscorbett>
Submitted on:  Fri 01 Dec 2017 05:44:22 PM UTC  
Category:  overall font problem Severity:  3 - Normal
Item Group:  character substitution issue Status:  Proceeding
Privacy:  Public Assigned to:  Steve White <Stevan_White>
Open/Closed:  Open Release:  development

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Sun 03 Dec 2017 06:41:19 PM UTC, comment #5: 


I think the arguments are weak either way. 

If you say western superscript digits are conventionally used on Tamil letters, I feel that is good enough reason to make them look nicer by providing special substitutions for them.

And maybe the universality of western digits in particular justifies making nice super/subscript forms for that set available for every script.

I disagree with your remark "it shouldn't matter".  The point is, if the user specifies superscripts in the correct, reasonable way, they get superscripts, features or not.  In normal circumstances, to specify an OpenType feature for this purpose is just wrong -- for several reasons.

Steve White <Stevan_White>
Project AdministratorIn charge of this item.
Sun 03 Dec 2017 04:35:45 PM UTC, comment #4: 

The digits are ASCII, not Tamil.

It shouldn’t matter how the user specifies superscripts, whether in HTML or some other format. From the font’s point of view it is all the same: the 'sups' feature is activated.

David Corbett <dscorbett>
Sun 03 Dec 2017 09:33:58 AM UTC, comment #3: 

Are those small digits you mention Arabic or Tamil?

I'm not sure that it's best to restrict special super/subscripts of a given script to that script.  The main reason was to keep features for separate scripts somewhat separated.

But I think the rest of your argument glosses over some technical issues, especially -- how is the user specifying super/subscripts, and what actually happens when they do?

Within an application environment, such as a browser, the preferred way is to produce superscript text specify the text to be superscripted, as with the HTML tag <sup>.  If nice special forms of the letters exist in the font, those should be used by lower software layers for rendering.  This is the role of the OpenType fetures we're discussing. Failing that, the original glyph is scaled and raised -- the user gets their superscript.

It is also possible in modern browsers to directly request OpenType font features.  But this is very dodgy: it's font-dependent, non-standardized behavior, very likely to break.  In HTML, it doesn't carry the semantic weight that the HTML tag does.  We test it, but this is not the normal way for a user to specify sub/superscripts.

Steve White <Stevan_White>
Project AdministratorIn charge of this item.
Fri 01 Dec 2017 11:24:00 PM UTC, comment #2: 

Tamil uses small digits to transcribe the Sanskrit letters the Tamil alphabet has lost, which is why I chose that example; but really, real-life examples for each script should not be necessary. If a user of the font specifies that a character should be superscript, and the font has a superscript glyph for the character, why should the font not produce the superscript glyph?

David Corbett <dscorbett>
Fri 01 Dec 2017 09:47:20 PM UTC, comment #1: 


The restriction was deliberate.  I don't know if it's the best way to go.

I haven't witnessed Latin (or Aribic numeral) superscripts on Tamil letters before your example.  Maybe... an English book on Tamil, with superscript footnotes?

I have my doubts that this is something that really happens. Maybe you could elaborate, or give a real-life example.

Steve White <Stevan_White>
Project AdministratorIn charge of this item.
Fri 01 Dec 2017 05:44:22 PM UTC, original submission:  

In FreeSerif, common-script characters like digits and punctuation do not get super- or subscripted with 'sups', 'subs', or 'sinf' unless near a character in one of a few scripts, like Latin or Cyrillic. This is because those features’ lookups do not apply to all scripts. They should.

data:text/html;charset=utf-8,<div style="font: 300px FreeSerif; font-feature-settings: 'sups'">%E0%AE%952

David Corbett <dscorbett>


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    Follow 3 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2017-12-03 Stevan_White StatusNeed info => Proceeding
    2017-12-01 Stevan_White StatusNone => Need info
        Assigned toNone => Stevan_White

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