I haven't been following this thread very closely, but subset fonts are and
will be important for complex script support, since some Arabic and related
fonts have thousands of glyphs, of which only a small subset is typically
used on a given page or in a document.

One further issue with complex script support is that not all glyphs in
certain fonts have an encoding entry, e.g., in an Arabic TTF font, there may
be glyph's whose indices does not have a forward mapping in the CMAP. In
some systems, this is addressed by using a lower level OS interface when
drawing, one that uses glyph indices directly (rather than character codes
to be mapped through an encoding vector); however, in the FOP IF interfaces,
only character codes are used. As a consequence, the complex script support
gets around this by dynamically creating new entries in the CMAP (or
equivalent encoding vector), using Unicode private use characters, to map to
glyph indices that are emitted by complex script processing, but which do
not normally have a CMAP entry.

In this scenario, it is essential to create an embedded font that includes
the referenced glyphs as well as the dynamically generated CMAP entries.
This is presently handled in the PDF renderer with no additional effort,
however, I have not yet addressed this in the PS or other renderers, so I
may very well have to modify the current mechanism if it is not practical to
use this approach with other renderers.


On Thu, Nov 11, 2010 at 9:50 AM, Chris Bowditch

> Hi All,
> On 09/11/2010 14:43, Jeremias Maerki wrote:
>> On 09.11.2010 14:48:30 Vincent Hennebert wrote:
>>> There may be an interest in fully embedding a font for PostScript
>>> output. IIUC there may be a print manager that pre-processes PostScript
>>> files, extracts embedded fonts to store them somewhere and re-use them
>>> whenever needed. It can then strip the font off subsequent files and
>>> substantially lighten them, speeding up the printing process.
>> It makes the files smaller, but that will be the only thing that
>> improved printing performance. The PS interpreter still has to parse and
>> process the actual resource. It also needs to be noted that extracting
>> subset fonts doesn't make sense. I've already added the unique-ification
>> prefix to the TTF font names (like in PDF) to avoid problems like that.
> Yes I agree extracting subset fonts doesn't make sense, but extracting a
> fully embedded font does have plenty of business applications. Which is
> precisely why the introduction of a setting is required here. In some cases
> it is important to bring the file size down; enter the subsetting feature.
> Subsetting is particularly useful when creating print stream with a
> relatively small number of pages, i.e. 100 or less and you have large
> Unicode fonts to support Eastern character sets.
>  In other situations people using FOP want to be able to create large Print
> streams to send to Print Bureaus. Print Bureaus tends to use software to
> parse Print streams rather than sending them directly to a printer. Those
> processes will often need to be able to process the fonts, which they can
> only do if the full font is embedded rather than a subset. As you already
> noted above, extracting a subset if useless.
>  What’s the purpose of the ‘encoding’ parameter? It looks to me like
>>> users don’t care about what encoding is used in the PDF or PostScript
>>> file. All they want to have is properly printed documents that use their
>>> own fonts. I think that parameter should be removed in favour of Mehdi’s
>>> proposal, which IMO makes much more sense from a user perspective.
>> I don't know if it's necessary. That's why I wrote that maybe additional
>> research may be necessary. If we don't have it, we may have to build up
>> a /CIDMap that covers Unicode because there is otherwise no information
>> in the font which character indices correspond to which glyph as long as
>> we use /Registry (Adobe) /Ordering (Identity). Or: you configure a CID
>> map (encoding) that is tailored to the kind of document you want to
>> produce. The Unicode /CIDMap could result in rather big /CIDMap arrays
>> (65535 * 4 = 256KB) with lots of pointers to ".notdef".
> From a user's perspective, the encoding parameter is too technical and most
> user's ill not understand its purpose. If possible I would like to reach a
> consenus on what we should do and then remove the parameter to help cut down
> the complexity of configuring fonts. As you noted there are now a
> bewildering number of options.
>  Before continuing with this there should be a broad understanding how
>> non-subset TrueType fonts shall be handled in PostScript (and PDF where
>> you can make the same case). Otherwise, a change like Mehdi proposed
>> doesn't improve anything.
> Are you asking what the business use case is for fully embedded fonts as
> opposed to subset fonts. The ability to post process is the most important
> use case. If the fonts are subset it become difficult to merge Postscript
> files together or extract the font. Both are fairly common at Print bureaus.
>  Granted, there would be some redundancy with the referenced-fonts
>>> element. But is the additional flexibility of regexp really useful in
>>> the first place? I’m not too sure. Maybe that could be removed too.
>> I don't want that removed. I've been grateful for its existence more
>> than once. With the regexp I can make sure that, for example, all
>> variants of the "Frutiger" font are not embedded: Frutiger 45 Light,
>> Frutiger 55 Roman etc. etc.
> I concur the regexp stuff in the font referencing is useful. We can use it
> to change the way whole font families are referenced without having to list
> every font.
>  Anyway, I don't like constantly changing the way fonts are configured.
>> There's enough confusion with the way it's currently done already. I
>> won't veto a change like that but I'm not happy with it.
> I understand what you are saying there are a lot of options, but then the
> requirements around fonts are complex so there is no escaping a comlex
> configuration file.
> Thanks,
> Chris
>  Vincent
>>> On 09/11/10 12:45, Jeremias Maerki wrote:
>>>> Hi Mehdi,
>>>> I'm against that since we already have mechanisms to control some of
>>>> these traits and this would overlap with them. For example, we have the
>>>> referenced-fonts element
>>>> (http://xmlgraphics.apache.org/fop/trunk/fonts.html#embedding)
>>>> which controls whether we embed or not. And we have the encoding-mode
>>>> attribute on the font element to control if single-byte or cid mode
>>>> should be used. Granted, that's not exactly what you're after, but I
>>>> believe this already covers 95% of the use cases if not more.
>>>> The only thing you can't currently do is embed a full font in CID mode
>>>> (or reference it). The problem here is the character map that should be
>>>> used when in CID mode. I think that would require some research first so
>>>> we know how best to handle this. For example, referencing only makes
>>>> sense if a TrueType font can be installed directly on the printer. But
>>>> then, the question is in which mode the characters can be addressed.
>>>> Single-byte (like we currently fall back to) is probably not a problem
>>>> unless you need to print Asian documents. Please note that we also don't
>>>> support full TTF embedding/referencing in CID mode in PDF documents. So
>>>> I'm not sure if we really need that at the moment.
>>>> If we do, I believe it would generally suffice to extend encoding-mode
>>>> from (auto|single-byte|cid) to (auto|single-byte|cid|cid-full). We may
>>>> need a "cmap" parameter then to change the default CMap (currently
>>>> "Identity-H" like in PDF) since our subsetting code uses custom
>>>> mappings,
>>>> not Unicode or any other encoding scheme (like "90ms-RKSJ-H").
>>>> On 09.11.2010 12:08:36 mehdi houshmand wrote:
>>>>> Hi,
>>>>> I'm working on making TTF subset embedding configurable such that a
>>>>> user can opt for either full font embedding, subset embedding or just
>>>>> referencing, this would be extending the work Jeremias submitted. I
>>>>> was considering adding a parameter to the font configuration file
>>>>> called "embedding" with 3 possible values "none", "subset" and "full".
>>>>> This would allow the user to configure the embedding mode on a font by
>>>>> font basis. What do people think about this proposal?
>>>>> Thanks
>>>>> Mehdi
>>>> Jeremias Maerki
>> Jeremias Maerki

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