[smufl-discuss] Re: Microtonal accidentals

[Hartmut]

Thank you Grzegorz and Emil for your technical advice. However, I still
don't get diacritics or ligature substitutions to work under Windows.
Although I am not totally sure that I have made everyting correctly, I
think there are some principal problems with OpenType features and the
Private Use Area. I have found several discussions on this topic:
http://forum.fontlab.com/index.php?topic=6580.0
http://forum.fontlab.com/index.php?topic=2690.0
http://www.mail-archive.com/unicode@.../msg08067.html

The quintessence is: Windows does not invoke any glyph transformations
for PUA characters.

There seem to be some exceptions if PUA characters are combined with
other characters. We could think about (ab-)using normal diacritic code
points (e.g. U+02C6 and U+02C7) as up and down arrows. But I am not even
sure if this helps because the base character (the accidental) would
still be from the PUA.

It was also mentioned in this list that there are problems with
diacritics or ligatures in html. So maybe we should drop the idea
completely. That's a pity because I really liked the idea.

Hartmut

On 10.06.2013 14:07, Grzegorz Rolek wrote:

>
> On Jun 8, 2013, at 12:45 AM, Hartmut Lemmel wrote:
>
>> I am trying to create a font where arrows are placed on top of accidentals like diacritics. I am using FontForge and I have created anchor points in the accidental glyph and in the arrow glyph. The anchor class is defined in the GPOS table of the font. In the preview of FontForge the arrows are nicely positioned on the accidentals.
>> I have installed the font under Windows and I haven't found a single application that would display the glyph sequence <accidental,combining arrow> correctly.
>
> There might be several issues involved, and I'll try to address two of them here, but please keep in mind that I don't have access to any Windows machine to actually test it, so this is all based on the things I've read.
>
> First. If your target font is a TrueType-flavoured font, does it also have the digital signature (DSIG) table? Otherwise it won't be recognized by Windows as an OpenType font, and for that matter no features will work. For more details why this is so, and how to make a dummy DSIG table, please see the Typophile thread at http://typophile.com/node/90383. I've also found Microsoft's own utilities for checking and signing fonts at http://microsoft.com/typography/developers/dsig/dsig.aspx (no idea how recent all this is).
>
> Second. Uniscribe, the text shaping library in Windows, uses different layout engines for different scripts it encounters in the text stream, each of them triggering different set of features required to properly shape the stream. This means that a script-specific feature won't be applied to a stream of characters that appear to be from a different script that doesn't normally require the feature in question. For example, in case of Arabic, the engine used will apply the required ligatures (rlig) feature as it's required for Arabic, but the engines that are not supposed to deal with it could just skip it. This, by the way, begs the question, how does Uniscribe behave for characters in the PUA?
>
> Normally, the <accidental,combining arrow> and similar sequences should be best handled under either the mark positioning feature (http://microsoft.com/typography/otspec/features_ko.htm#mark) or the character composition feature (http://microsoft.com/typography/otspec/features_ae.htm#ccmp), depending on what lookup types are used: the character composition mentions only the substitution-type lookups, and the mark positioning only the attachment-type ones. I assume your case should thus involve the mark positioning (mark) feature.
>
> You might also find it helpful to read a Typophile thread at http://typophile.com/node/13042 and, linked in the thread by John Hudson, his own and quite a detailed essay on Windows glyph processing from Microsoft Typography.
>
>
>
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