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-rw-r--r--Build/source/libs/harfbuzz/harfbuzz-src/src/hb-ot-layout-gsubgpos-private.hh31
1 files changed, 26 insertions, 5 deletions
diff --git a/Build/source/libs/harfbuzz/harfbuzz-src/src/hb-ot-layout-gsubgpos-private.hh b/Build/source/libs/harfbuzz/harfbuzz-src/src/hb-ot-layout-gsubgpos-private.hh
index 0c423526861..005ed21d804 100644
--- a/Build/source/libs/harfbuzz/harfbuzz-src/src/hb-ot-layout-gsubgpos-private.hh
+++ b/Build/source/libs/harfbuzz/harfbuzz-src/src/hb-ot-layout-gsubgpos-private.hh
@@ -996,17 +996,38 @@ static inline bool apply_lookup (hb_apply_context_t *c,
if (!delta)
continue;
- /* Recursed lookup changed buffer len. Adjust. */
+ /* Recursed lookup changed buffer len. Adjust.
+ *
+ * TODO:
+ *
+ * Right now, if buffer length increased by n, we assume n new glyphs
+ * were added right after the current position, and if buffer length
+ * was decreased by n, we assume n match positions after the current
+ * one where removed. The former (buffer length increased) case is
+ * fine, but the decrease case can be improved in at least two ways,
+ * both of which are significant:
+ *
+ * - If recursed-to lookup is MultipleSubst and buffer length
+ * decreased, then it's current match position that was deleted,
+ * NOT the one after it.
+ *
+ * - If buffer length was decreased by n, it does not necessarily
+ * mean that n match positions where removed, as there might
+ * have been marks and default-ignorables in the sequence. We
+ * should instead drop match positions between current-position
+ * and current-position + n instead.
+ *
+ * It should be possible to construct tests for both of these cases.
+ */
end += delta;
- if (end <= int (match_positions[idx]))
+ if (end < int (match_positions[idx]))
{
/* End might end up being smaller than match_positions[idx] if the recursed
- * lookup ended up removing many items, more than we have had matched.
+ * lookup ended up removing too many items.
* Just never rewind end back and get out of here.
* https://bugs.chromium.org/p/chromium/issues/detail?id=659496 */
end = match_positions[idx];
- /* There can't be any further changes. */
break;
}
@@ -1019,7 +1040,7 @@ static inline bool apply_lookup (hb_apply_context_t *c,
}
else
{
- /* NOTE: delta is negative. */
+ /* NOTE: delta is non-positive. */
delta = MAX (delta, (int) next - (int) count);
next -= delta;
}