[EXT] Re: l3backend: adding new DVI specials?

Zdenek Wagner zdenek.wagner at gmail.com
Fri Feb 14 13:16:53 CET 2020

pá 14. 2. 2020 v 12:52 odesílatel Philip Taylor <P.Taylor at rhul.ac.uk> napsal:
> Zdenek Wagner wrote:
> > Yes, but as was already mentioned, pdftex can distinguish between a
> > PDF mode and a DVI mode but cannot guess the DVI driver. The
> > regression test must follow specification and select the DVI driver
> > used further in the test. I am afraid there is no other possibility.
> > XeTeX invokes xdvipdfmx explicitly so it can know which driver is
> > used, it is not the case of pdftex in the DVI mode.
> It seems to me (as an outsider to this discussion) that the best
> solution — as opposed to the simplest — would be to define a universal
> \special which all drivers would be required to "understand", and thus
> not generate a warning.  The data within this special could then use
> (for example) keyword:value pairs to pass different information — or
> none at all — to different drivers.
This would be equivalent to developing a new language which would make
little sense if we already have postscript and PDF. In addition, my
zwpagelayout package supports setting "black overprint". If PDF is
created directly, a PDF operator is used to change the graphic state.
Both pdftex and xdvipdfmx send a direct PDF code. However, pdftex
works with graphic states and indirect objects in a different way than
xdvipdfmx, so that I must not only send a different \special but alse
send it in a different time (i.e. place of the document). dvips cannot
use a PDF code but a PS \special. And again, in a different time. If I
want to output SVG, there is no way, black overprint is not supported
(it is not allowed to change the graphic state in an image which
should be includable). Now it is important to wanr a user that a
requested feature is not implemented. Without warning a user would
complain that the result is not what she wanted hence warning is
important and unavoidable. On the other hand, (x)dvipdfm(x) nowadays
properly interprets many dvips specials as well as many pdf literals.

> Philip Taylor

Zdeněk Wagner

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