How to add palt and vpal features?

Does anybody know the syntaxes of these features (Proportional Alternate Halfwidths and Proportional Alternate Vertical Metrics)?

JanekZ's picture

It looks like they are "Single adjustment positioning"
http://www.adobe.com/devnet/opentype/afdko/topic_feature_file_syntax.htm...
So in .fea file:

lookup vpalProportionalAlternateVertic {
lookupflag 0;
pos \A <100 100 200 -300>;
} vpalProportionalAlternateVertic;

lookup paltProportionalAlternateMetric {
lookupflag 0;
pos \B <-200 -300 0 0>;
} paltProportionalAlternateMetric;

BTW palt is Proportional Alternate Widths not Halfwidths

lunde's picture

This should help. Below are excerpts from the 'palt' and 'vpal' GPOS features in our KozGoPr6N-Medium OpenType font:

feature palt {
position \634 <-20 0 -500 0>;
position \638 <-250 0 -500 0>;
position \674 <-480 0 -500 0>;
} palt;

feature vpal {
position \638 <0 250 0 -500>;
position \7887 <0 20 0 -500>;
position \7899 <0 480 0 -500>;
} vpal;

The font is CID-keyed, so the glyph references are CIDs. CIDs 634, 638, and 674 correspond to U+3001, U+30FB, and U+FF08, respectively. These are good examples, because they represent a left-justified (U+3001), right-justified (U+FF08), and centered (U+30FB) glyph. The vertical form of CID+634 is CID+7887, and that of CID+674 is CID+7899. CID+638 is used for both horizontal and vertical writing, because it is centered in the em-box.

Although the new advance widths are 500 units, meaning half-width, there is no requirement that this be the case. We simply decided to implement them that way for this particular font.

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