[tex-live] dviout: color specials in the are not page independent

Hironobu Yamashita h.y.acetaminophen at gmail.com
Thu Apr 19 18:13:00 CEST 2018

Hi Igor,

> When dvi file is opened by dviout, some strange message appears:
> dviout color specials in the are not page independent. When I agree
> for modifying the file, everything works. However, what is there in
> my file that dviout dislikes?
> Within MiKteX (there is  dvi-viewer yap) no warning appears like that.

dviout checks page-independency and shows a warning,
and yap does not; that is all what differs.

A DVI file is a sequence of commands which form "a machine-like language".
In the simplest situation, the appearance of a page can be determined
from commands encapsulated in that single page. Therefore, when
a DVI viewer is going to display a single page from a multipage DVI file,
the viewer is required to parse only that single page. This is true in
most case, because a DVI file is

* (always) page-independent if no \special commands are involved
* (sometimes) page-independent if \special commands appears

However, the real world is not so simple as expected; there is a possibility
that the commands in preceeding page affect the page appearance.
It occurs when \special's are involved, like page color, text color etc.
MWE (the first and second pages should be in red):

first,\newpage second

To handle this situation, dviout correctly parses throughout a DVI file,
from the start page (with a help of a program dvispc.exe background).
I guess dviout is calling a user's attention for safety in this complex situation.

I don't know much about yap, but if the second page of MWE above
is shown in red, yap should be doing similar too (without showing any
warnings to user).

Hironobu Yamashita

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