[fontforge-users] Can lookups create space for marks?

[marty39]

I'm making an all-caps font intended for close line spacing, so there's no
room for accent marks. It's turned into an exercise in supporting Latin,
Greek and Cyrillic scripts in a variety of European languages. To
accommodate the necessary marks above and below, I want to use small caps if
there is one mark, petite caps if there are two marks, maybe even
teeny-weeny caps if there are three, and position the base glyph above the
baseline if there's a mark below it.

I can take care of that for glyphs that I precompose in Fontforge. Can I use
lookups to do the same substitutions and positioning for accented glyphs
that are composed in a text layout application? If so, how?



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[Georg Duffner]

Hi,

I’d use the ccmp feature for this purpose, put all letters sc-letters

Post by marty39
I'm making an all-caps font intended for close line spacing, so there's no
room for accent marks. It's turned into an exercise in supporting Latin,
Greek and Cyrillic scripts in a variety of European languages. To
accommodate the necessary marks above and below, I want to use small caps if
there is one mark, petite caps if there are two marks, maybe even
teeny-weeny caps if there are three, and position the base glyph above the
baseline if there's a mark below it.
I can take care of that for glyphs that I precompose in Fontforge. Can I use
lookups to do the same substitutions and positioning for accented glyphs
that are composed in a text layout application? If so, how?
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[marty39]

Georg, I've seen code like that before but not within FontForge. I suppose
it's for a feature file. I know there's a way to export and import feature
files and snippets in FontForge, and I think I've found some usable info on
how to write them.

What would I do to make room for accent marks below the base glyph? Try
writing a contextual positioning lookup? Or create more substitutions with
HISCLETTERS and HIPCLETTERS? I would need, not just a class @ACCENTS, but
classes @TOPACCENTS and @BOTTOMACCENTS. I can do that.

Next question is which applications implement the ccmp feature. I did
something in imitation of the sample attached to the 27 August 2008
developer topic "Contextual positioning," and it didn't do anything in
NeoOffice Writer. Maybe writing it in a feature file would work better. Or
maybe implementing anything beyond precomposed glyphs is a mere learning
exercise.



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[Georg Duffner]

Post by marty39
Georg, I've seen code like that before but not within FontForge. I suppose
it's for a feature file. I know there's a way to export and import feature
files and snippets in FontForge, and I think I've found some usable info on
how to write them.

Yes, that code is for feature files. The documentation can be found at
http://www.adobe.com/devnet/opentype/afdko/topic_feature_file_syntax.html

Post by marty39
What would I do to make room for accent marks below the base glyph? Try
writing a contextual positioning lookup? Or create more substitutions with

These cases should go to the same lookup and you have to take care of
the order. When the opentype engine goes through a string it tries to
match rule after rule in the active lookups. After matching a rule in a
lookup, the opentype engine passes on the next lookup in the font, so
you have to make sure to write the most specific or complex rule on top
and the least complex rule at the bottom of the lookup:

sub @LETTERS' @TOPACCENTS @BOTTOMACCENTES by @HIPCLETTERS;
sub @LETTERS' @BOTTOMACCENTS @TOPACCENTES by @HIPCLETTERS;
sub @LETTERS' @TOPACCENTS @TOPACCENTES by @PCLETTERS;
sub @LETTERS' @TOPACCENTS by @SCLETTERS;
sub @LETTERS' @BOTTOMACCENTS @BOTTOMACCENTES by @HIPCLETTERS;
sub @LETTERS' @BOTTOMACCENTS by @HISCLETTERS;

And of course, if that might occur, this and similar rules should come
even first:
sub @LETTERS' @TOPACCENTS @TOPACCENTS @BOTTOMACCENTES by
@HIMINUSCULELETTERS;
sub @LETTERS' @TOPACCENTS @BOTTOMACCENTS @BOTTOMACCENTES by
@SUPERHIMINUSCULELETTERS;

Post by marty39
Next question is which applications implement the ccmp feature. I did
something in imitation of the sample attached to the 27 August 2008
developer topic "Contextual positioning," and it didn't do anything in
NeoOffice Writer. Maybe writing it in a feature file would work better. Or
maybe implementing anything beyond precomposed glyphs is a mere learning
exercise.

According to the Opentype layout tag registry, the ccmp feature should
be on by default
(https://www.microsoft.com/typography/otspec/features_ae.htm#ccmp). I’d
consider it a bug in the application, if it isn’t.

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[marty39]

Post by Georg Duffner
I’d use the ccmp feature for this purpose, put all letters sc-letters

I just had a horrible thought. All accented letters can be made by adding
one or more of the class @ACCENTS to one of the class @SCLETTERS or
@PCLETTERS (only slightly oversimplified). These classes are all of
manageable size. The task is more complicated, but still manageable, when
composites with single or double marks above and single marks below are
considered.

But Fontforge can make doubly accented letters by adding an accent to an
already accented letter. If text layout applications can similarly add
accents to already accented letters, then I would have to write rules to
change the size of any singly accented letter when an accent is added to it.
Considering the possibility of double marks above with single marks below,
and all the combinations that could generate them, the task becomes
unmanageable. Do any applications do that?

BTW, why does FontForge do that?



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[Georg Duffner]

Post by marty39

Post by Georg Duffner
I’d use the ccmp feature for this purpose, put all letters sc-letters

I just had a horrible thought. All accented letters can be made by adding
@PCLETTERS (only slightly oversimplified). These classes are all of
manageable size. The task is more complicated, but still manageable, when
composites with single or double marks above and single marks below are
considered.
But Fontforge can make doubly accented letters by adding an accent to an
already accented letter. If text layout applications can similarly add
accents to already accented letters, then I would have to write rules to
change the size of any singly accented letter when an accent is added to it.
Considering the possibility of double marks above with single marks below,
and all the combinations that could generate them, the task becomes
unmanageable. Do any applications do that?
BTW, why does FontForge do that?

What you describe is the mechanism to generate glyphs at certain code
points, that consist of a base glyph and accent glyphs. FF probably does
that because it’s the most simplistic approach, but I don’t know.

I’d circumvent these problems by decomposing precomposed glyphs in the
ccmp feature. I’d put that in a lookup that would come before the
previously discussed one:

sub Agrave by A.sc gravecomb;
sub Aacute by A.sc acutecomb;
sub Acircumflex by A.sc uni0302;

and so on. So, when one types in the sequence <Á> <uni0300> (however you
do that in your application), the Á will first be replaced by A.sc and
acutecomb when passing through the first lookup. When passing through
the second lookup, the engine will already see the sequence <A.sc
acutecomb uni0302> and can match it with the line
sub @LETTERS' @ACCENTS @ACCENTS by @PCLETTERS;


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