OpenType features for geeks

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kostas's picture
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Joined: 31 Jul 2009 - 12:26am
OpenType features for geeks
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hi, everybody
i’m a fontlab beginner and i would like to know if there is any way to understand all that “chinese” code input for OpenType features. Spending a day to understand how to “ignore a substitute” (from FontLab manual) but nothing!!! Any help for the complete idiot?

Konstantinos Siskakis
Anagrafi
Greece

Mark Simonson's picture
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Joined: 3 Dec 2001 - 11:00am
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The logic for "ignore" can be confusing. It's best to think of it as a filter that excludes things. Or as an "if not" statement.

Theunis de Jong's picture
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Joined: 22 Apr 2008 - 5:06pm
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Since FontLab uses the AFDKO, the Adobe site is a good resource (IIRC, the FontLab manual does mention a few deviations). Your ignore line can be found here:

Specifying exceptions to the Chain Sub rule

The most confusing part of it is it also needs a at least one part tagged with a ' (in regular substitutions this marks the to-be-replaced glyph(s)).

Christopher Slye's picture
Joined: 5 Oct 2006 - 11:03am
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Speaking of those 'ignore sub' statements: Within any lookup in a features file (which often means within a feature, unless you've specified lookups within a feature), scanning stops at the first match. So, in OpenType layout, if 'sub f i by f_i' matches, then that substitution is made, and everything in the lookup after that is ignored/skipped. The 'ignore sub' statements function exactly like any other 'sub' statement in this regard, except that instead of performing a substitution, nothing is done.

So, the statement 'ignore sub x f' i' by f_i' can be read as "if f and i is preceded by x, do nothing." This is a match, like everything else, and subsequent lines in the lookup are skipped.

Don't know if that actually helps! :)

Christopher Timothy Dean's picture
Joined: 22 Oct 2006 - 10:49pm
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While we're on the topic, anyone know how to get at OpenType features in Pages?

(Mac, iWork)

Mark Simonson's picture
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Joined: 3 Dec 2001 - 11:00am
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Sure: Select the text, open the Fonts panel (command-T), and choose "Typography..." from the the pop-up menu at the bottom with the gear icon. If the text is set in an OT font, the features will show up there.