Fix merging of loca tables

src/calibre/utils/fonts/sfnt/loca.py

@@ -6,7 +6,7 @@ __license__   = 'GPL v3'
 __copyright__ = '2012, Kovid Goyal <kovid at kovidgoyal.net>'
 __docformat__ = 'restructuredtext en'
 
-from struct import calcsize, unpack_from, pack
+import array, sys
 from operator import itemgetter
 from itertools import repeat
 
@@ -14,16 +14,22 @@ from calibre.utils.fonts.sfnt import UnknownTable
 from polyglot.builtins import iteritems, range
 
 
+def four_byte_type_code():
+    for c in 'IL':
+        a = array.array(c)
+        if a.itemsize == 4:
+            return c
+
+
 class LocaTable(UnknownTable):
 
     def load_offsets(self, head_table, maxp_table):
-        fmt = 'H' if head_table.index_to_loc_format == 0 else 'L'
-        num_glyphs = maxp_table.num_glyphs
-        sz = calcsize(('>%s'%fmt).encode('ascii'))
-        num = len(self.raw)//sz
-        self.offset_map = unpack_from(('>%d%s'%(num, fmt)).encode('ascii'),
-                self.raw)
-        self.offset_map = self.offset_map[:num_glyphs+1]
+        fmt = 'H' if head_table.index_to_loc_format == 0 else four_byte_type_code()
+        locs = array.array(fmt)
+        locs.fromstring(self.raw)
+        if sys.byteorder != "big":
+            locs.byteswap()
+        self.offset_map = locs.tolist()
         if fmt == 'H':
             self.offset_map = [2*i for i in self.offset_map]
         self.fmt = fmt
@@ -37,8 +43,14 @@ class LocaTable(UnknownTable):
         '''
         Update this table to contain pointers only to the glyphs in
         resolved_glyph_map which must be a map of glyph_ids to (offset, sz)
+        Note that the loca table is generated for all glyphs from 0 to the
+        largest glyph that is either in resolved_glyph_map or was present
+        originally. The pointers to glyphs that have no data will be set to
+        zero. This preserves glyph ids.
         '''
+        current_max_glyph_id = len(self.offset_map) - 2
         max_glyph_id = max(resolved_glyph_map or (0,))
+        max_glyph_id = max(max_glyph_id, current_max_glyph_id)
         self.offset_map = list(repeat(0, max_glyph_id + 2))
         glyphs = [(glyph_id, x[0], x[1]) for glyph_id, x in
                     iteritems(resolved_glyph_map)]
@@ -54,16 +66,16 @@ class LocaTable(UnknownTable):
 
         vals = self.offset_map
         max_offset = max(vals) if vals else 0
-        max_short_offset = 65535 * 2
-        if self.fmt == 'L' and max_offset <= max_short_offset:
+        if max_offset < 0x20000 and all(l % 2 == 0 for l in vals):
             self.fmt = 'H'
-        if self.fmt == 'H':
-            if max_offset > max_short_offset:
-                self.fmt = 'L'
-            else:
-                vals = [i//2 for i in vals]
+            vals = array.array(self.fmt, (i // 2 for i in vals))
+        else:
+            self.fmt = four_byte_type_code()
+            vals = array.array(self.fmt, vals)
 
-        self.raw = pack(('>%d%s'%(len(vals), self.fmt)).encode('ascii'), *vals)
+        if sys.byteorder != "big":
+            vals.byteswap()
+        self.raw = vals.tostring()
     subset = update
 
     def dump_glyphs(self, sfnt):

src/calibre/utils/fonts/sfnt/maxp.py

@@ -42,5 +42,5 @@ class MaxpTable(UnknownTable):
                 setattr(self, f, val)
 
     def update(self):
-        vals = [getattr(self, f) for f in self._fields]
+        vals = [getattr(self, f) for f in self.fields]
         self.raw = pack(self._fmt, *vals)

src/calibre/utils/fonts/sfnt/merge.py

@@ -11,6 +11,7 @@ from functools import partial
 def merge_truetype_fonts_for_pdf(*fonts):
     # only merges the glyf and loca tables, ignoring all other tables
     all_glyphs = {}
+    ans = fonts[0]
     for font in fonts:
         loca = font[b'loca']
         glyf = font[b'glyf']
@@ -21,12 +22,17 @@ def merge_truetype_fonts_for_pdf(*fonts):
                 if sz > 0:
                     all_glyphs[glyph_id] = glyf.glyph_data(offset, sz, as_raw=True)
 
-    ans = fonts[0]
-    loca = ans[b'loca']
     glyf = ans[b'glyf']
+    head = ans[b'head']
+    loca = ans[b'loca']
+    maxp = ans[b'maxp']
     gmap = OrderedDict()
     for glyph_id in sorted(all_glyphs):
         gmap[glyph_id] = partial(all_glyphs.__getitem__, glyph_id)
     offset_map = glyf.update(gmap)
     loca.update(offset_map)
+    head.index_to_loc_format = 0 if loca.fmt == 'H' else 1
+    head.update()
+    maxp.num_glyphs = len(loca.offset_map) - 1
+    maxp.update()
     return ans

src/calibre/utils/fonts/sfnt/subset.py

@@ -64,9 +64,9 @@ def subset_truetype(sfnt, character_map, extra_glyphs):
 
     # Update the loca table
     loca.subset(glyph_offset_map)
-    head.index_to_loc_format = 1 if loca.fmt == 'L' else 0
+    head.index_to_loc_format = 0 if loca.fmt == 'H' else 1
     head.update()
-    maxp.num_glyphs = len(glyph_offset_map)
+    maxp.num_glyphs = len(loca.offset_map) - 1
 
 # }}}