[dvipdfmx] Possible extensions to color special support

[Shunsaku Hirata]

After some consideration I am now thinking that having
a different set of special commands (other than pdf:) is
appropriate for multiple color stack implementation, like

  \special{pdfcolorstackinit 1 page direct (0 g)}
  \special{pdfcolorstack 1 push (1 0 0 rg)}
  \special{pdfcolorstack 1 set    (0 0 1 rg)}
  \special{pdfcolorstack 1 current}
  \special{pdfcolorstack 1 pop}

Here PDF string objects are used for specifying PDF
literals.

Although they are not only for "color" but as they are for
PDFTeX compatibility, pdfcolorstack is used.

I already finished implementing them and after some
tests they would be available.

Thanks,
Shunsaku Hirata

2020年9月3日(木) 6:38 Joseph Wright <joseph.wright at morningstar2.co.uk>:
>
> On 02/09/2020 16:30, Shunsaku Hirata wrote:
> > Hi Joseph,
> >
> >> The first area is the stroke/fill ('non-stroke') split. At present,
> >> "pdf:bcolor" pushes both stroke and non-stroke color to the stack. One
> >> can set the two separately, but only by using a PDF literal, which
> >> therefore does not go to the stack. This can lead to 'interesting'
> >> outcomes if the two are inter-mixed. Would something like
> >>
> >>       pdf:strokecolor / pdf:sc
> >>       pdf:fillcolor / pdf:fc
> >>
> >> be possible to set only the stroke or fill. Both of these would still
> >> 'pair' with pdf:ec, in the same way in pdfTeX one can do
> >>
> >>       \pdfcolorstack <n> push {0.1 0.2 0.3 0.4 k}
> >>       ...
> >>       \pdfcolorstack <n> pop
> >>
> >> as well as
> >>
> >>       \pdfcolorstack <n> push {0.1 0.2 0.3 0.4 k 0.1 0.2 0.3 0.4 K}
> >>       ...
> >>       \pdfcolorstack <n> pop
> >
> > So pdf:sc in the example above pushes specified stroke color
> > and current fill color onto the color stack.
> >
> > Both adding new specials and extending existing pdf:bc special
> > to accept "stroke" and "fill" keyword like
> >
> >    pdf:bc fill [1 0 0]
> >
> > can be easily done.
>
> A keyword would also work fine: which ever is easier to code for you, we
> can work with.
>
> >> The second thing is highlighted in some ways by that pdfTeX example: the
> >> existence of more than one stack. Additional stacks are useful for
> >> footnotes, transparency, etc., and so are less easily supported using
> >> dvipdfmx than with pdfTeX. (When using dvips, one can code in the stacks
> >> manually using PostScript.) The current 'main' stack approach must of
> >> course not change, so any pdf:bc or similar will always use this main
> >> 'stack 0'. A possible way to add additional stacks would be to work
> >> closer to pdfTeX, i.e. have them take 'raw' PDF specs, so perhaps
> >> pdf:colorstack/pdf:cs
> >>
> >>       \special{pdf:cs 1 push 0.1 0.2 0.3 0.4 k}
> >>       ...
> >>       \special{pdf:cs 1 pop}
> >>
> >> i.e. syntax
> >>
> >>       pdf:cs <n> [push|pop] <PDF literal>
> >>
> >
> > I rather want to avoid using "PDF literal" which can affect outside
> > the special command as much as possible since this makes it
> > difficult to manage things properly.
> >
> > Anyway, I will consider extending dvipdfmx to support such features.
> >
> > For transparency support, I already added new special commands
> > pdf:bxgstate and pdf:exgstate which can be used as
> >
> >    \special{pdf:bxgstate << /CA 0.5 /ca 0.5 >>}
> >    Transparent text.
> >    \special{pdf:exgstate}%
> >
> > where a dictionary object representing ExtGState should be supplied
> > as an argument.
>
> I'll explore these specials: I was not aware of them.
>
> Joseph