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Add some additional comments about packing state machine.

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This commit is contained in:
Garret Rieger 2022-06-27 18:28:02 +00:00
parent d92fd2665c
commit 8196166e53
1 changed files with 11 additions and 0 deletions
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11
Lib/fontTools/ttLib/tables/otBase.py
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@ -38,6 +38,14 @@ class OTLOffsetOverflowError(Exception):
return repr(self.value)
class RepackerState(IntEnum):
# Repacking control flow is implemnted using a state machine. The state machine table:
#
# State | Packing Success | Packing Failed | Exception Raised |
# ------------+-----------------+----------------+------------------+
# PURE_FT | Return result | PURE_FT | Return failure |
# HB_FT | Return result | HB_FT | FT_FALLBACK |
# FT_FALLBACK | HB_FT | FT_FALLBACK | Return failure |
# Pack only with fontTools, don't allow sharing between extensions.
PURE_FT = 1
@ -126,6 +134,9 @@ class BaseTTXConverter(DefaultTable):
elif state == RepackerState.PURE_FT:
return self.tryPackingFontTools(writer)
elif state == RepackerState.FT_FALLBACK:
# Run packing with FontTools only, but don't return the result as it will
# not be optimally packed. Once a successful packing has been found, state is
# changed back to harfbuzz packing to produce the final, optimal, packing.
self.tryPackingFontTools(writer)
log.debug("Re-enabling sharing between extensions and switching back to "
"harfbuzz+fontTools packing.")