SLxfig supports -DSLXFIG_RENDER_LATEX_AS_TRANSPARENT_PNG

When the symbol SLXFIG_RENDER_LATEX_AS_TRANSPARENT_PNG is defined,
any LaTeX output is rendered as transparent png (instead of eps)
-- which may be desirable when other transparent pngs are used.

In this case, its probably best to render the Xfig output to svg.
The following can be used to generate a pdf from an intermediate svg:

  xfig_set_output_driver ("pdf", "fig2dev -L svg %I %B.svg && rsvg-convert -f pdf %B.svg > %O && rm %B.svg");
  % or
  xfig_set_output_driver ("pdf", "fig2dev -L svg %I %B.svg && inkscape %B.svg --export-pdf=%O && rm %B.svg");

The current implementation requires the following programs to be
installed:

   dvipng         (debian package: dvipng)
   rsvg-convert   (debian package: librsvg2-bin)

