[dvipdfmx] Multiple color stacks

[Joseph Wright]

Hello all,

A whilst ago, dvipdfmx was extended to support multiple color stacks. 
These are set up independent of the 'original' color stack, which can be 
accessed using either "color push" or "bc" specials. When this was 
introduced, I spotted an issue in that after some operations, dvipdfmx 
resets the color to that from this original stack. We had hoped at that 
stage that this could all be handled in the macro layer.

We recently tried to switch the main LaTeX graphics .def files to use 
multiple color stacks, and immediately ran into issues. Also at the 
macro level we can catch some 'hidden' resets, we can't deal with users 
having simple bcontent/econtent pairs around - these come up from 
various sources. So we had to back out using the multiple stacks. As an 
example, the following shows the behaviour:

\special{pdfcolorstackinit 0 (0 g 0 G)}
\special{pdfcolorstack 0 push (0 0 1 rg)}
Some text
\special{pdf:bcontent}
\special{pdfcolorstack 0 push (1 0 0 rg)}
Intermediate text
\special{pdf:econtent}
Some more text
\bye

At present, it seems that whilst the stack support looks OK, it's really 
not usable for day-to-day LaTeX documents, as we simply can't deal with 
the reset requirement at the macro level. If you look at a pdfTeX example

\pdfcolorstack 0 push {0 0 1 rg}
Some text
\pdfsave
\pdfcolorstack 0 push {1 0 0 rg}
Intermediate text
\pdfrestore
Some more text
\bye

then all works 'out of the box'.

What I think we need for the multiple stacks to work is for the 
'classical' one to be the same as pdfcolorstack 0, so

     \special{color push Black} -> \special{pdfcolorstack 0 push (0 g)}
     \special{pdf:bc [0 0 1]} -> \special{pdfcolorstack 0 push (0 0 1 rg)}

and with therefore "pdfcolorstackinit 0" not required. We'd then be able 
to use the same code more-or-less in pdfTeX, LuaTeX and dvipdfmx routes.

As it stands, I can't risk using the multiple stack approach, which is a 
real shame.

Joseph