Change font for org LaTeX-preview

Question

I successfully use org LaTeX-preview to have my formulas displayed as images in my org-mode documents. There is one problem I am facing, though: I need the LaTeX math font to be upright instead of slanted. This is easily solved in an ordinary LaTeX-document by adding \usepackage[math-style=upright]{unicode-math}. For some reason, I have trouble getting it to work with LaTeX preview. This is my package specification for preview images:

(setq org-latex-packages-alist '(
("" "amssymb" t)
("" "turnstile" t)  ; for Turnstiles
("" "centernot" t)  ; for striked through Turnstiles
("" "mathpartir" t) ; for inference patterns
("math-style=upright" "unicode-math" t) ; for upright Math font
))

If I understand how org-latex-packages-to-string works, the above specification should produce the desired result. I even manually added "\usepackage[math-style=upright]{unicode-math}" to org-format-latex-header:

(setq org-format-latex-header "\\documentclass{article} 
\\usepackage[usenames]{color}
\[PACKAGES]
\[DEFAULT-PACKAGES]
\\usepackage[math-style=upright]{unicode-math}         % added package 
\\pagestyle{empty}             % do not remove
% The settings below are copied from fullpage.sty
\\setlength{\\textwidth}{\\paperwidth}
\\addtolength{\\textwidth}{-3cm}
\\setlength{\\oddsidemargin}{1.5cm}
\\addtolength{\\oddsidemargin}{-2.54cm}
\\setlength{\\evensidemargin}{\\oddsidemargin}
\\setlength{\\textheight}{\\paperheight}
\\addtolength{\\textheight}{-\\headheight}
\\addtolength{\\textheight}{-\\headsep}
\\addtolength{\\textheight}{-\\footskip}
\\addtolength{\\textheight}{-3cm}
\\setlength{\\topmargin}{1.5cm}
\\addtolength{\\topmargin}{-2.54cm}"
)

This did not work either. Do you have an idea what I can do to have the LaTeX-fragments displayed upright instead of slanted?

Edit: The value of org-preview-latex-process-alist is

((dvipng :programs
         ("latex" "dvipng")
         :description "dvi > png" :message "you need to install the programs: latex and dvipng." :image-input-type "dvi" :image-output-type "png" :image-size-adjust
         (1.0 . 1.0)
         :latex-compiler
         ("latex -interaction nonstopmode -output-directory %o %f")
         :image-converter
         ("dvipng -D %D -T tight -bg Transparent -o %O %f"))
 (dvisvgm :programs
          ("latex" "dvisvgm")
          :description "dvi > svg" :message "you need to install the programs: latex and dvisvgm." :image-input-type "dvi" :image-output-type "svg" :image-size-adjust
          (1.7 . 1.5)
          :latex-compiler
          ("latex -interaction nonstopmode -output-directory %o %f")
          :image-converter
          ("dvisvgm %f -n -b min -c %S -o %O"))
 (imagemagick :programs
              ("latex" "convert")
              :description "pdf > png" :message "you need to install the programs: latex and imagemagick." :image-input-type "pdf" :image-output-type "png" :image-size-adjust
              (1.0 . 1.0)
              :latex-compiler
              ("pdflatex -interaction nonstopmode -output-directory %o %f")
              :image-converter
              ("convert -density %D -trim -antialias %f -quality 100 %O")))

Also, I have (setq org-latex-create-formula-image-program 'dvipng) in my .init file. This is why the value of org-preview-latex-default-process is dvipng.

Answer 1

Thanks to d125q's comments, I solved the issue. It was twofold:

First and foremost, unicode-math is a package which only works with XeTeX or LuaTeX, but org by default compiles with LaTeX. This is why you need the preview images to be generated by XeTeX or LuaTeX. This is my configuration:

(setq org-preview-latex-process-alist
       '((dvipng :programs
         ("lualatex" "dvipng")
         :description "dvi > png" :message "you need to install the programs: latex and dvipng." :image-input-type "dvi" :image-output-type "png" :image-size-adjust
         (1.0 . 1.0)
         :latex-compiler
         ("lualatex -output-format dvi -interaction nonstopmode -output-directory %o %f")
         :image-converter
         ("dvipng -fg %F -bg %B -D %D -T tight -o %O %f"))
       (dvisvgm :programs
          ("latex" "dvisvgm")
          :description "dvi > svg" :message "you need to install the programs: latex and dvisvgm." :use-xcolor t :image-input-type "xdv" :image-output-type "svg" :image-size-adjust
          (3 . 1.5)
          :latex-compiler
          ("xelatex -no-pdf -interaction nonstopmode -output-directory %o %f")
          :image-converter
          ("dvisvgm %f -n -b min -c %S -o %O"))
       (imagemagick :programs
              ("latex" "convert")
              :description "pdf > png" :message "you need to install the programs: latex and imagemagick." :use-xcolor t :image-input-type "pdf" :image-output-type "png" :image-size-adjust
              (1.0 . 1.0)
              :latex-compiler
              ("xelatex -no-pdf -interaction nonstopmode -output-directory %o %f")
              :image-converter
              ("convert -density %D -trim -antialias %f -quality 100 %O"))))

I copied it off from here and am open for any suggestions (the images are generated more slowly than before).

Secondly, LuaTeX requires org-latex-preview to generate .dvi images (instead of .png or .pdf files). You can configure this by adding (setq org-preview-latex-default-process 'dvisvgm) to your .init file. But caution: You need the dvisvgm dependency, which ships with latex-extra-utils, as well as an emacs build capable of dealing with svg files. This usually is the case, but especially if you build it from source like me, you need to double-check to (1) have librsvg2-dev installed and (2) use --with-rsvg in ./configure.

If those two points are solved, org-latex-preview should compile the images with LuaTeX and thus be able to use the unicode-math package when generating the preview image if you add it to org-latex-packages-alist, for example by adding (add-to-list 'org-latex-packages-alist '("math-style=upright" "unicode-math" t)) to your .init file.