https://issues.apache.org/bugzilla/show_bug.cgi?id=52477

--- Comment #7 from quamis <quamis+...@gmail.com> 2012-01-18 11:27:19 UTC ---
(In reply to comment #6)

> That wouldn't necessarily fix the issue here. Fully embedding a font means 
> that
> the pseudo-unique prefix isn't used, however this isn't necessarily a good
> thing. A parser like ghostscript, could and apparently does assume that if 2
> fonts have the same name (prefix or not) that they are the same font. This is
> an assumption  that I've made previously and has proved manifestly naive. 
> Also,
> any implementation CANNOT clash within the same document. Using a glyph subset
> idea, there could be a scenario in which the 2 fonts with the same glyph
> subsets produce the same prefix.

But if 2 fonts have the same glyph subsets used within a document, then it
wouldn't be necessary to include them twice, so no clashing would occur. I
think that glyph subsets are a good idea, but i do realize that it would be
more complex to implement.

> 
> We have to be careful what we're supporting here. There is no standardised
> method to identify a font, since anyone can call any font by any name. I don't
> agree that making the prefix "more unique" (not sure there is a scale by which
> something can be measured unique, it's binary, it is or it isn't), would help
> here, because given time, inevitably you'll get a clash. Then what?

Because the prefix is 6 chars long, its inevitably that one would eventually
get a clash, if he uses enough millions of different fonts within the same
file. But this is an acceptable limitation.

> The prefixes are 6 chars long, the guys at Adobe made no indication that they
> wanted it to be unique in a global sense, only within a document.

Yes, the Adobe guys probably meant that the prefix should be unique within the
same file and it would be the pdf reader/writer's job to handle duplicate fonts
coming from different fonts. It makes sense. This is why i think both fop and
gs handle this particular case wrong, as they both assumed things about that
prefix, and it seems that this assumptions are now proven wrong. 
gs in particular should warn about merging files with embedded fonts, either
when merging, or at least in the manual, or a "known-issues" page.

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