Glyph Substitution

[Trevor]

Hi

How to I make / add glyph font substitutions for / to a font.
For example I want that when ever the diacritic Unicodes +u05BD and +u05B4 follow one another that they should be replace with the diacritic Unicode +u05C9

I know there are some free downloads from Adobe & Microsoft but I don't have a clue of what to do with them and from what I understand Microsoft's program erases any information that already exits in the font.

[Allan Murray]

I think you are talking about OpenType feature glyph substitutions.

There is a good introduction here: ilovetypography.com/OpenType/opentype-features.html

Some specifics for Hebrew fonts: www.microsoft.com/typography/otfntdev/hebrewot/features.htm

I will attempt to give you an example of how you can do this using the ccmp (Glyph de/composition) OpenType feature, This might not be the best feature tag to use (you might need to do some research into Hebrew OpenType feature standards), but will give you an idea of how it works.

Go to font menu / opentype features and press view files
Insert the attached text file (HebrewDiacritic.feax) into that directory,
Close the dialog box and then go back to: font / opentype features. Tick the box next to HebrewDiacritic.

Provided that the glyphs have been created in the font, the feature will be saved in the font.

Note: you will have to be using an OpenType compatible application (eg InDesign) to be able to use the feature (see the first link - it has a list of applications)


Contents of HebrewDiacritic.feax :

# Substitutes HEBREW_POINT_METEG(afii57839) HEBREW_POINT_METEG(afii57839)
# with user defined glyph uni05C9

languagesystem DFLT dflt;
languagesystem hebr dflt;

feature ccmp {

sub afii57839 afii57793 by uni05C9;

} ccmp;

Paste this into notepad and rename the file to HebrewDiacritic.feax

Note: afii57839 and afii57793 are the PostScript names for Unicode 05BD and 05B4. You can change the PostScript name for uni05C9 glyph if you want to (right click on the glyph when it is displayed in the mapping window, set to glyph list).

See also the Type 3.0 manual page 24: OpenType layout features.

[Trevor]

Thanks Murry for your comprehensive answer,
The basic substitution works BUT because I don't have a way of assigning my user defined glyph as a "mark" it is treated as a "simple" and as such amongst other issues cannot be repositioned in indesign using adjust diacritic positioning. Substituting to a diacritic unincode might work (didn't try it) but is not an acceptable solution.

I installed VOLT and managed to make a useable font with substitutions, letter kerning, mark to simple and mark to mark positioning but did come up with the following issues.

1) When opening a otf font created with Type the glyph editor of VOLT does not show the glyph shapes . If the otf is converted to a ttf then the glyphs are displayed properly.

2) As well know ALL OPEN TYPE DATA IS LOST when opening a font in VOLT this is to say the least a pain in the neck if one is making adjustments to an existing font which already has possibly humungous open-type tables included in it . I appreciate that incorporating a full functioning VOLT equivalent into Type would be very difficult to code perhaps something we can look out for in Type 56.0 but the ability to designate glyph types (Simple, Ligature, Mark & Component) the improvement of the kerning feature to include the positioning options of VOLT i.e. the addition of Single adjustment, Caret positioning and Cursive and Anchor attachments. The addition of a Right To Left option in the kerning feature is obviously important to me. If you could add on these features it would be great for not just for me and other RTL fontist but also for the throngs of script uses who use accents and diacritics as used by I think the vast majority of languages. Adding these features would I'm sure make to the fan of the multitudes I am aware that one can use adobes AFDKO for these features without wiping out the OT tables but as AFDKO seems to be as user friendly as wiping a lions nose I'm too scared to try it out.

3) My Hebrew font is listed in Indesign as amongst the English fonts and not the Hebrew ones. The font does however work in indesign but not in Word 2007 which treats it as an English font, rendering it as completely useless for use in Word .

Please note I did tick in Type Hebrew as to active and un-tick Latin. In Volt I added <hebr> as the script and <IWR > as the language.

Type 3.0 dose not give the option under font name to designate the font as either Hebrew or Arabic or a great variety of languages this should be very easy to fix and if you could do so in the immediate future it would be much appreciated . I am uncertain that this is the cause of the problem as I lack knowledge and experience in the field. Any ideas?

Looking forward for your feedback.

Regards

Trevor

[Allan Murray]

Trevor,


1) This appears to be the case with all .otf fonts - not just those created in Type 3.0.

2) The current version of Type (3.0.014 - full version) supports these OpenType features (see pages 35-37 in the manual for more info):

Single substitution
Multiple substitution
Alternate substitution
Ligature substitution
Single adjustment positioning
Pair adjustment positioning

You can also designate glyphs as: baseglyphs, ligatures, marks or components. But because the current version of Type does not support MarkToBase, MarkToLigature or MarkToMark attachments, designating glyphs as marks is not really of much use. This would be the code to add to the end of your .feax file designate your user defined glyph as a mark:
gdef {
baseglyphs default
marks uni05C9;
} gdef;

There are other OpenType features still to be added. It is possible that mark-mark, mark-base and mark-ligature may be added as an update to version 3.1 (but probably not to the first release of 3.1 which is due later this year).

3) I think maybe you have ticked Hebrew with the mapping window set to Unicode Script. You need to tick 1255 Hebrew when the mapping window is set to Codepages (Preferences menu).

4) There are some languages missing from the naming table. It is simple to add these, and I will do so within the next few weeks, Apologies for not keeping the language list updated.

I am interested in making the software more useful for non-Latin based languages.

Cheers,
Allan

[Trevor]

Hi Allan,

Long time no contact,
I thought I replied to your last post a couple of years ago, sorry about the delay and thanks for your responce.
I was wondering if you had added support MarkToBase, MarkToLigature or MarkToMark attachments in the latest version of type or if you have any plans to.

Regards
Trevor

[Allan Murray]

Trevor,

Those OpenType features have not been added to Type font editor.

Expanding the range of OpenType features is on the 'to do' list, but is not scheduled for the next round of updates - which will be mainly focused on adding font/glyph preview options.

Allan