Coding question

Jeff Peters

Hello, please help. In this line – what does the ' after space do and stand for? Thank you!

 sub @figures space' @numerators by thinspace;

Kent Lew

The single quote signifies the target in a contextual substitution (GSUB Lookup Type 5/6 or GPOS Lookup Type 7/8).

cf.: https://www.adobe.com/devnet/opentype/afdko/topic_feature_file_syntax.html#2.d

Kent Lew

P.S. So the example you posted, then, translates to “when a space glyph is preceded by any member of the @figures class and followed by any member of the @numerators class, it should be replaced by a thinspace glyph.”

André G. Isaak

That indicates the target of substitution in a contextual rule.

sub X Y' Z by W # with tick

will replace any string of the form XYZ with XWZ.

Without the tickmark you'd have a ligature replacement rule:

sub X Y Z by W # no tick

would simply replace XYZ with W.

Note that the above can also be written as

sub X' Y' Z' by W # multiple ticks

which makes it clearer that all three elements on the left side of the rule are being replaced.

The rule you give, which I assume is from a 'frac' feature, substitutes spaces with thinspaces but only when they follow a figure and are followed by a numerator.

Jeff Peters

Thought it would be something like that. Thanks again!

Jeff Peters

Only problem is, space isn't exchanged with thinspace in InDesign. When writing 2 1/8 for example. Any ideas why? The fraction part works, though. Here's the code:
(@numr0 being figures and @numr1 being numerators. Thinspace exists in the font and is mapped to uni2009...)

feature frac { # Fractions

sub one [slash fraction] two by onehalf;

sub one [slash fraction] four by onequarter;

sub three [slash fraction] four by threequarters;

lookup SlashToFraction {

ignore sub slash @figures @figures @figures @figures @figures @figures @figures @figures @figures @figures slash';

ignore sub slash' @figures @figures @figures @figures @figures @figures @figures @figures @figures @figures slash;

ignore sub slash @figures @figures @figures @figures @figures @figures @figures @figures @figures slash';

ignore sub slash' @figures @figures @figures @figures @figures @figures @figures @figures @figures slash;

ignore sub slash @figures @figures @figures @figures @figures @figures @figures @figures slash';

ignore sub slash' @figures @figures @figures @figures @figures @figures @figures @figures slash;

ignore sub slash @figures @figures @figures @figures @figures @figures @figures slash';

ignore sub slash' @figures @figures @figures @figures @figures @figures @figures slash;

ignore sub slash @figures @figures @figures @figures @figures @figures slash';

ignore sub slash' @figures @figures @figures @figures @figures @figures slash;

ignore sub slash @figures @figures @figures @figures @figures slash';

ignore sub slash' @figures @figures @figures @figures @figures slash;

ignore sub slash @figures @figures @figures @figures slash';

ignore sub slash' @figures @figures @figures @figures slash;

ignore sub slash @figures @figures @figures slash';

ignore sub slash' @figures @figures @figures slash;

ignore sub slash @figures @figures slash';

ignore sub slash' @figures @figures slash;

ignore sub slash @figures slash';

ignore sub slash' @figures slash;

sub @figures slash' @figures by fraction;

} SlashToFraction;

sub @numr0' fraction by @numr1;

sub @numr0' @numr1 fraction by @numr1;

sub @numr0' @numr1 @numr1 fraction by @numr1;

sub @numr0' @numr1 @numr1 @numr1 fraction by @numr1;

sub @numr0' @numr1 @numr1 @numr1 @numr1 fraction by @numr1;

sub @numr0' @numr1 @numr1 @numr1 @numr1 @numr1 fraction by @numr1;

sub @numr0' @numr1 @numr1 @numr1 @numr1 @numr1 @numr1 fraction by @numr1;

sub @numr0' @numr1 @numr1 @numr1 @numr1 @numr1 @numr1 @numr1 fraction by @numr1;

sub @numr0' @numr1 @numr1 @numr1 @numr1 @numr1 @numr1 @numr1 @numr1 fraction by @numr1;

sub @numr0' @numr1 @numr1 @numr1 @numr1 @numr1 @numr1 @numr1 @numr1 @numr1 fraction by @numr1;

sub [fraction @dnom1] @dnom0' by @dnom1;

sub @numr0 space' @numr1 by thinspace;

} frac;

Robin Mientjes

Your code, second to last line, says sub @numr0 space' @numr1 by thinspace; but I think it should be sub @figures space' @numr1 by thinspace;. You say @numr0 is the same as @figures, but, why do you then use both?

Jeff Peters

Yeah I know, I don't remember where I got the code from and it may be a mix from different sources, thus the two identical classes with different names. But should it matter, since they both include figures 0-9?

Craig Eliason

I think you need to separate the different types of changes you want to make into lookups. As it is, by the time the denominators are changed the code can't go back in the string to fix the space. 

• OT Cookbook on processing
• Tal Leming frac feature code

Jeff Peters

Yes, you might be right, Craig. Or could I execute the thinspace before the fraction, like this:

feature frac { # Fractions

sub one [slash fraction] two by onehalf;

sub one [slash fraction] four by onequarter;

sub three [slash fraction] four by threequarters;

sub @figures space' @figures [slash fraction] by thinspace;

lookup SlashToFraction {

ignore sub slash @figures @figures @figures @figures @figures @figures @figures @figures @figures @figures slash';

ignore sub slash' @figures @figures @figures @figures @figures @figures @figures @figures @figures @figures slash;

ignore sub slash @figures @figures @figures @figures @figures @figures @figures @figures @figures slash';

ignore sub slash' @figures @figures @figures @figures @figures @figures @figures @figures @figures slash;

ignore sub slash @figures @figures @figures @figures @figures @figures @figures @figures slash';

ignore sub slash' @figures @figures @figures @figures @figures @figures @figures @figures slash;

ignore sub slash @figures @figures @figures @figures @figures @figures @figures slash';

ignore sub slash' @figures @figures @figures @figures @figures @figures @figures slash;

ignore sub slash @figures @figures @figures @figures @figures @figures slash';

ignore sub slash' @figures @figures @figures @figures @figures @figures slash;

ignore sub slash @figures @figures @figures @figures @figures slash';

ignore sub slash' @figures @figures @figures @figures @figures slash;

ignore sub slash @figures @figures @figures @figures slash';

ignore sub slash' @figures @figures @figures @figures slash;

ignore sub slash @figures @figures @figures slash';

ignore sub slash' @figures @figures @figures slash;

ignore sub slash @figures @figures slash';

ignore sub slash' @figures @figures slash;

ignore sub slash @figures slash';

ignore sub slash' @figures slash;

sub @figures slash' @figures by fraction;

} SlashToFraction;

sub @numr0' fraction by @numr1;

sub @numr0' @numr1 fraction by @numr1;

sub @numr0' @numr1 @numr1 fraction by @numr1;

sub @numr0' @numr1 @numr1 @numr1 fraction by @numr1;

sub @numr0' @numr1 @numr1 @numr1 @numr1 fraction by @numr1;

sub @numr0' @numr1 @numr1 @numr1 @numr1 @numr1 fraction by @numr1;

sub @numr0' @numr1 @numr1 @numr1 @numr1 @numr1 @numr1 fraction by @numr1;

sub @numr0' @numr1 @numr1 @numr1 @numr1 @numr1 @numr1 @numr1 fraction by @numr1;

sub @numr0' @numr1 @numr1 @numr1 @numr1 @numr1 @numr1 @numr1 @numr1 fraction by @numr1;

sub @numr0' @numr1 @numr1 @numr1 @numr1 @numr1 @numr1 @numr1 @numr1 @numr1 fraction by @numr1;

sub [fraction @dnom1] @dnom0' by @dnom1;

} frac;

Jeff Peters

Thanks for the links, by the way.

Craig Eliason

Jeff Peters said:

Or could I execute the thinspace before the fraction

No, you don't want that, because it might thin spaces that are not part of a compound fraction (like in space-separated dates for example). 

Kent Lew

I don’t recommend executing the thinspace substitution before the fractions. Even though you’ve restricted it to a sequence that includes the slash or fraction.

The whole purpose of this particular fraction code is to be able to apply the {frac} feature at a global level and have it parse out fractions. That’s why all those ignore subs are written at the beginning, to skip over things like date format.

But if you execute your thinspace anywhere but the end (conditioned by the presence of a numerator), then you risk having thin spaces substituted in situations where it is not wanted when the feature is applied broadly. Perhaps rare, but still less desirable.

Just mark it for a separate lookup at the end. (Some implementations choose to leave out this option altogether.)

In Tal’s original feature code, all of those numerator and the denominator subs were each marked for separate lookups, which is how it all worked without marking the thinspace sub as such. But if you remove those explicit lookup designations (as your code has), then you need to mark the final sub as its own lookup.

BTW, Craig’s second link is missing a colon, so it’s broken as of this writing. Here is a corrected link: Fraction Fever 2. And be sure to read the post for the first version of the code, Fraction Fever, which explains a little more about what went into developing this routine and how it works.

Jeff Peters

Thanks all, I got it working now. Seems it got confused by the two figure classes and the extra lookup also did the trick.

Nick Shinn

Strictly speaking, you should create a special “space.thin” glyph, to preserve the original text.