Re: Bug report: Allow CFF based OT fonts with missing map table

[suzuki toshiya]

Dear Adam, Derek,

Adam, thank you for reminding that SFNT-wrapped PostScript fonts
on Apple platforms, it sounds reasonable attitude to handle such
incorrectly(?) embedded CFF font.

Derek, my understanding of current situation is:

1) currently FreeType simply raises an error for "head + CFF"
stream without special information. Even if a FreeType client
is capable to process such stream, the client has to catch all
errors and re-investigate the content of the stream. It is
"duplicating" of the font parsing.

2) the option best for the PDF rendering is "dealing with
head + CFF stream as simple CFF stream, ignoring head table".

3) another option better than current is "raising special
error indicating 'CFF is included, but other essential
tables for CFF OpenType are missing' and let the FreeType
client decide how deal such special case.

Is it correct?

I would try to make an artificial example by adding "head"
table to its internal CFF streams, to investigate how existing
PDF viewers handle such. I would ask how such PDF set the
font descriptor metadata to "head + CFF" stream in later.

I'm quite sorry for that I'm too busy to recover my PDF
playground in this month, I hope this issue is not immediate
to be resolved within a few days.

Regards,
mpsuzuki

On 2024/06/06 4:40, Adam Twardoch (List) wrote:
> My own focus is on PDF files. The PDF spec says that fonts declared as
> OpenType should be OpenType, and the files I'm looking at violate the
> spec. (PDF also supports standalone CFF fonts, so it's relatively
> little extra work for me to pull the CFF blob out of these bogus
> "OpenType" fonts, and handle it as a CFF font.)
>
> Oh yes, you're right there. However, this is a very general problem. Even though OpenType 
> is a Microsoft trademark, Microsoft had done a very poor job in explaining/defining what 
> is and what ISN'T an "OpenType font".
>
> Windows had been announcing OpenType fonts with a glyf table but without a DSIG table as 
> "TrueType" for many years, even though TrueType is an Apple trademark. So many end-users 
> for a long time associated CFF-based OpenType with "OpenType".
>
> And PDF has its own notion of font format "branding", and then there's a 
> question of how certain apps like Acrobat present these.
>
> I lost count of the different variants of fonts that "can exist" in a PDF a log 
> time ago. I guess a Type42 with a variable CFF2 table is also theoretically possible :) 
> Or with just CBDT, without glyf and CFFx.
>
> One thing for sure: on "desktop", certain fonts work out they don't, but they need to be kind of 
> "complete". But PDF has this flurry of "partial font resources" which makes it 
> extra-complex.
>
> A.