Re: [ft] Issues with fonts embedded in PDF

[Derek B. Noonburg]

On 29 Jan, address@hidden wrote:
> "Derek B. Noonburg" <address@hidden> wrote on Mon, 28 Jan 2008
> 12:08:59 -0800 (PST):
> 
>> On 28 Jan, Werner LEMBERG wrote:
>>
>>>> The TrueType fonts in question have broken table directories.  [...]
>>> 
>>> Hmm.  Would it be helpful to make xpdf as generous as Acroread is?
>>> The latter can display those fonts...
> 
> Actually... I'm opposed. If it were up to me to decide, I would reject
> all faulty files outright (except perhaps in a special "recovery
> mode"). Breaking syntax implies losing semantics. Excessive tolerance
> has brought us this tag-soup mess of a Web. In the long run, covering
> up errors makes everybody's lives more painful.

In principle, I agree.

Unfortunately, Xpdf "competes" with Acrobat in some senses.  There's a
general impression that, if Adobe Reader can display a PDF file, the
file must be ok, and if Xpdf (or ghostscript, or ...) fails, then it's a
bug in Xpdf.

So I try to report bugs in PDF generation software (and Jeremias has
been very quick to fix fop), but I also am somewhat forced to
incorporate workarounds into Xpdf.

In this case, the workaround is fairly general.  It simply ignores any
invalid entries in the TrueType table directory.  Xpdf already checked
for invalid entries; previously it threw an error and refused to handle
the font if there were any invalid entries.  I've found TrueType fonts
to be a *major* headache.  This is hardly the first problem I've
encountered.  There's code in Xpdf which rewrites TrueType files, fixing
a laundry list of known problems along the way.

Incidentally, there was some discussion a couple years ago about putting
together some sort of PDF validation tool.  It never really went
anywhere, unfortunately.  Though realistically, I'm not sure there would
be any way to convince folks writing PDF generating software to actually
use the validator.

- Derek