Kern with class subtables too (kern formats 2 and 3)

The kern table's class subtables, OpenType's and Apple's, as HarfBuzz
reads them (hb-aat-layout-kerx-table.hh, hb-ot-kern-table.hh): format 2's
class tables give byte offsets into a kerning array, format 3's byte
classes index a value list. Both go through the same pass as pairs
(marks skipped, the kerning split between the pair). Format 2 filters the
glyphs by the class tables' digests, as HarfBuzz's accelerator does, so a
digest's false positive reads class 0 there too; what a subtable reads
must lie within it, the last one's within the table. The build checks the
subtables as HarfBuzz's sanitizer does, and still refuses state machines
(format 1) and cross-stream kerning.

text/test-kern.py makes fonts with format 2 and 3 subtables in every
order, with the edge cases that reading has (value 1, glyphs outside a
table, offsets below the array or odd, values past a subtable's or the
table's end, classes and indexes past their counts): 24 fonts, 96 plans,
the same as HarfBuzz. make check runs it where fontTools is. HarfBuzz's
suite: 5017 of 5199 the same.

1 files changed, 2 insertions, 0 deletions

diff --git a/text/shape.h b/text/shape.h
index 690430c..e02f0e4 100644
--- a/text/shape.h
+++ b/text/shape.h
@@ -121,6 +121,8 @@ typedef struct {
     const unsigned char *sequences; /* variation sequences */
     uint32_t sequence_count;
     VegaTable gdef, gsub, gpos, kern;
+    VegaDigest *kern_sets;          /* each kern subtable's left and right glyphs (format 2's), as HarfBuzz digests them */
+    uint32_t kern_subtables;
     VegaTable fallback;             /* Arabic fallback shaping's lookups, a GSUB table */
     uint32_t fallback_count;
     uint8_t fallback_features[7];   /* what each is for: init, medi, fina, isol, rlig x3 (0..6) */