Re: [Freetype] Ambiguously Undefined Glyphs [was: Mozilla needs some info on Xft]

[Brian Stell]

Juliusz Chroboczek wrote:
> ...
> To quote myself, what you're doing is ``clearly bogus.''  See also
> Antoine Leca's note on the FreeType list.

Could you describe what specifically is ``cleary bogus''.

> Anyway, back to your problem.  If these fonts work with Windows, there
> must be something we don't understand (I'm sure Windows doesn't do
> something that stupid), so there must be some way of disambiguating
> these Ambiguously Undefined Glyphs (AUGs) from blank glyphs.
> 
> It is difficult to say without seeing a dump of the relevant parts of
> the fonts, but I'll take a guess.  Assuming that the AUGs' cmap
> entries point at valid loca entries, and that the loca entries point
> at valid glyph data (you have checked that, haven't you?), I'd be
> tempted to believe that they're trying to optimise the size of a type
> 4 cmap by having non-zero cmap entries that are aliased to the
> undefined glyph through the loca table.

I did chat with him specifically about this problem and I belive 
I understood what he did to test for the "broken" glyphs.

Take a look at Erik's test:

http://lxr.mozilla.org/seamonkey/source/gfx/src/windows/nsFontMetricsWin.cpp#637

which was checked in with this comment:

  3.37 <address@hidden> 16 Apr 1999 13:01
  Fixed bugs 2522 and 4875. Switched from FONTSIGNATURE to cmap to
figure
  out which glyphs are available. Removed FONT_SWITCHING ifdef.

As I read line 661 it is checking the LOCA table to see 
if the character's glyph has data 0 length.

651   DWORD newLen = GetFontData(aDC, LOCA, 0, buf, len);
652   if (newLen != len) {
653     PR_Free(buf);
654     return nsnull;
655   }
656   if (isLong) {
657     DWORD longLen = ((len / 4) - 1);
658     *aMaxGlyph = longLen;
659     PRUint32* longBuf = (PRUint32*) buf;
660     for (PRUint32 i = 0; i < longLen; i++) {
661       if (longBuf[i] == longBuf[i+1]) {
662         buf[i] = 1;
663       }
664       else {
665         buf[i] = 0;
666       }
667     }
668   }

These blank chars are later used to test if we shoule mark the
font as having a particular char.

(longBuf becomes isSpace)

1407             if (glyph < maxGlyph) {
1408               if (isSpace[glyph]) {
1409                 if (SHOULD_BE_SPACE(c)) {
1410                   ADD_GLYPH(map, c);
1411                 }
1412               }
1413               else {
1414                 ADD_GLYPH(map, c);
1415               }
1416             }


FreeType2 does not provide access to the LOCA table so I could not
do the test in Erik's code or the test you suggested. Instead
I load the glyph and look at the count of contours.

> P.S. I want Erik back!

He just got married and he's taking time off (and having alot of
fun!).

-- 
Brian Stell
mailto:address@hidden