[Devel] cmap in webdings

[Dirck Blaskey]

I have a pdf file with an embedded True Type font, webdings,
that has some oddities with its cmap, so FT_Get_Char_Index
wasn't working.

The cmap doesn't explicitly cover the character ranges, 
most of the entries have startCount == endCount.

Here is a patch to Freetype 2.0.9 sfnt/ttcmap.c;
The patch should work with the current development snapshot.

In theory, there might be a problem with the patch,
when looking for characters that _really_ aren't there.  
Maybe an additional check for startCount == endCount?
Is there any safe way to be sure?

A better fix might be to do some doctoring after the load;
the 'length' value from the dump looks right, maybe
that can be used to validate the fixups at load time.

The patch goes just above the:
    
    return 0;

  Found:

in code_to_index4().

Here's the patch:

735a736,753
> 
>     /* [[ 2002.5.20 for webdings.tt embedded in a pdf file
>        the table doesn't cover the glyphs we want, 
>        but the information is there.  
>        if RangeOffset == 0 assuming endCount is next StartCount - 1
> 
>        the last_segment optimization above won't catch this
>     */
>     limit--;
>     for ( seg4 = cmap4->segments; seg4 <= limit; seg4++ )
>     {
>       if ( seg4->idRangeOffset == 0 &&
>            charCode >= (FT_UInt)seg4->startCount && 
>            seg4 == limit || charCode < seg4[1].startCount )
>         goto Found;
>     }
>     /* ]] */
> 

Here's the cmap dump from the font:
Subtable  1.   Platform ID:   0
               Specific ID:   3
               'cmap' Offset: 0x0000024A
       ->Format: 4 : Segment mapping to delta values
  Length:  100
  Version: 0
  segCount: 9  (X2 = 18)
  searchRange: 16
  entrySelector: 3
  rangeShift: 2
  Seg   1 : St = 0009, En = 000A, D =      0, RO =    18, gId# = 0
  Seg   2 : St = 000C, En = 000D, D =      0, RO =    20, gId# = 2
  Seg   3 : St = 0020, En = 0020, D =    -29, RO =     0, gId# = N/A
  Seg   4 : St = 002F, En = 002F, D =    -29, RO =     0, gId# = N/A
  Seg   5 : St = 005C, En = 005C, D =    -29, RO =     0, gId# = N/A
  Seg   6 : St = 007C, En = 007C, D =    -29, RO =     0, gId# = N/A
  Seg   7 : St = 2028, En = 2029, D =      0, RO =    14, gId# = 4
  Seg   8 : St = 21B8, En = 21B8, D =  -8589, RO =     0, gId# = N/A
  Seg   9 : St = FFFF, En = FFFF, D =      1, RO =     0, gId# = N/A
  glyphIdArray[0] =    3 (Offset = 0058)
  glyphIdArray[1] =    3 (Offset = 005A)
  glyphIdArray[2] =    3 (Offset = 005C)
  glyphIdArray[3] =    3 (Offset = 005E)
  glyphIdArray[4] =    3 (Offset = 0060)
  glyphIdArray[5] =    3 (Offset = 0062)

  Which Means:
     1. Char 0009 -> Index 3
        Char 000A -> Index 3
     2. Char 000C -> Index 3
        Char 000D -> Index 3
     3. Char 0020 -> Index 3
     4. Char 002F -> Index 18
     5. Char 005C -> Index 63
     6. Char 007C -> Index 95
     7. Char 2028 -> Index 3
        Char 2029 -> Index 3
     8. Char 21B8 -> Index 43