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86 lines
3.2 KiB
Python
86 lines
3.2 KiB
Python
from struct import unpack_from, calcsize, pack, error as struct_error
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from ebook_converter.utils.fonts.sfnt import (UnknownTable, FixedProperty,
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max_power_of_two)
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from ebook_converter.utils.fonts.sfnt.errors import UnsupportedFont
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__license__ = 'GPL v3'
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__copyright__ = '2012, Kovid Goyal <kovid at kovidgoyal.net>'
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__docformat__ = 'restructuredtext en'
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class KernTable(UnknownTable):
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version = FixedProperty('_version')
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def __init__(self, *args, **kwargs):
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super(KernTable, self).__init__(*args, **kwargs)
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self._version, self.num_tables = unpack_from(b'>HH', self.raw)
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if self._version == 1 and len(self.raw) >= 8:
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self._version, self.num_tables = unpack_from(b'>LL', self.raw)
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self.headerfmt = b'>HH' if self._version == 0 else b'>LL'
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def restrict_to_glyphs(self, glyph_ids):
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if self._version not in {0, 0x10000}:
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raise UnsupportedFont('kern table has version: %x'%self._version)
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offset = 4 if (self._version == 0) else 8
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tables = []
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for i in range(self.num_tables):
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if self._version == 0:
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version, length, coverage = unpack_from(b'>3H', self.raw, offset)
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table_format = version
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else:
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length, coverage = unpack_from(b'>LH', self.raw, offset)
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table_format = coverage & 0xff
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raw = self.raw[offset:offset+length]
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if table_format == 0:
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raw = self.restrict_format_0(raw, glyph_ids)
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if not raw:
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continue
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tables.append(raw)
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offset += length
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self.raw = pack(self.headerfmt, self._version, len(tables)) + b''.join(tables)
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def restrict_format_0(self, raw, glyph_ids):
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if self._version == 0:
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version, length, coverage, npairs = unpack_from(b'>4H', raw)
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headerfmt = b'>3H'
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else:
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length, coverage, tuple_index, npairs = unpack_from(b'>L3H', raw)
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headerfmt = b'>L2H'
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offset = calcsize(headerfmt + b'4H')
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entries = []
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entrysz = calcsize(b'>2Hh')
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for i in range(npairs):
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try:
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left, right, value = unpack_from(b'>2Hh', raw, offset)
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except struct_error:
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offset = len(raw)
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break # Buggy kern table
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if left in glyph_ids and right in glyph_ids:
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entries.append(pack(b'>2Hh', left, right, value))
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offset += entrysz
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if offset != len(raw):
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raise UnsupportedFont('This font has extra data at the end of'
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' a Format 0 kern subtable')
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npairs = len(entries)
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if npairs == 0:
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return b''
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entry_selector = max_power_of_two(npairs)
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search_range = (2 ** entry_selector) * 6
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range_shift = (npairs - (2 ** entry_selector)) * 6
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entries = b''.join(entries)
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length = calcsize(headerfmt + b'4H') + len(entries)
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if self._version == 0:
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header = pack(headerfmt, version, length, coverage)
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else:
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header = pack(headerfmt, length, coverage, tuple_index)
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return header + pack(b'>4H', npairs, search_range, entry_selector,
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range_shift) + entries
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