Split kerning by script, not by direction #636
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Given a pair and mapping between glyph names and a set of scripts, split the pair into (potentially) multiple pairs each with a dominant script.
| allSecondScripts = {} | ||
| for g in self.firstGlyphs: | ||
| if g not in glyphScripts: | ||
| glyphScripts[g] = set(["Zyyy"]) |
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Please use a named constant for "Zyyy".
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They are added to all other lookups as well, right? The main deficiency I see in this PR is lack of support for Script_Extensions data-file. That's not a huge deal though. If glyphs with script A and B are kerned and you insert that kern in both lookups for A and for B, that handles most of the cases already. |
No, but the common lookup is added to all script/language combinations
I think it does support this. <key>comma-ar</key>
<dict>
<key>gba-nko</key>
<integer>-120</integer>
<key>lam-ar</key>
<integer>-30</integer>
</dict>
<key>gba-nko</key>
<dict>
<key>gba-nko</key>
<integer>-20</integer>
</dict>
<key>lam-ar</key>
<dict>
<key>lam-ar</key>
<integer>50</integer>
</dict>
<key>three</key>
<dict>
<key>three</key>
<integer>-50</integer>
</dict>becomes lookup kern_Arab {
lookupflag IgnoreMarks;
pos comma-ar lam-ar <-30 0 -30 0>;
pos lam-ar lam-ar <50 0 50 0>;
} kern_Arab;
lookup kern_Nkoo {
lookupflag IgnoreMarks;
pos comma-ar gba-nko <-120 0 -120 0>;
pos gba-nko gba-nko <-20 0 -20 0>;
} kern_Nkoo;
lookup kern_Common {
lookupflag IgnoreMarks;
pos three three -50;
} kern_Common;(check out test_split_pair in the tests.) |
|
Thanks for the explanation. This is neat. LGTM! |
This reverts commit bdac61e. # Conflicts: # Lib/ufo2ft/featureWriters/kernFeatureWriter.py # Lib/ufo2ft/util.py
Revert "Split kerning by script, not by direction (#636)"
Currently we split kerning into lookups based on a single factor, horizontal direction. However, shaping engines will perform script segmentation and so there will never be any cross-script kerning. By splitting the kerning into lookups based on the script of the glyphs involved, we can produce smaller lookups for large multi-script fonts, hopefully causing less overflows (faster compilation) and reducing file space by giving the binary compiler a better starting point for splitting lookups into subtables.
There are a few failsafes, such as glyphs without identifiable scripts (as well as purely common-script glyphs) go into a "Common" pot which is added to DFLT/dflt.
This may be easiest to review commit by commit; the changes are fairly small and self-contained apart from f56eaf6 which is the big rewrite.