Re: babel latex headers and image generation commands

[Matt Huszagh <huszaghmatt@gmail.com>]

Ok, here's an implementation that seems to be working pretty well so
far.

`org-latex-img-process` is the new customization. Most of the execute
function is unaltered, but I've added the condition:
```
             ((and (not imagemagick)
                   (assoc extension org-latex-img-process))
```

Here's the change in full.

```
    (setq org-latex-pdf-process
          '("latexmk -f -interaction=nonstopmode -output-directory=%o %f"))

    (setq org-latex-img-process
          '(("svg" . ("dvisvgm %f -P -n -b min -o %O"))))

    (defun org-babel-execute:latex (body params)
      "Execute a block of Latex code with Babel.
This function is called by `org-babel-execute-src-block'."
      (setq body (org-babel-expand-body:latex body params))
      (if (cdr (assq :file params))
          (let* ((out-file (cdr (assq :file params)))
	         (extension (file-name-extension out-file))
	         (tex-file (org-babel-temp-file "latex-" ".tex"))
	         (border (cdr (assq :border params)))
	         (imagemagick (cdr (assq :imagemagick params)))
	         (im-in-options (cdr (assq :iminoptions params)))
	         (im-out-options (cdr (assq :imoutoptions params)))
	         (fit (or (cdr (assq :fit params)) border))
	         (height (and fit (cdr (assq :pdfheight params))))
	         (width (and fit (cdr (assq :pdfwidth params))))
	         (headers (cdr (assq :headers params)))
	         (in-buffer (not (string= "no" (cdr (assq :buffer params)))))
	         (org-latex-packages-alist
	          (append (cdr (assq :packages params)) org-latex-packages-alist)))
            (cond
             ((and (string-suffix-p ".png" out-file) (not imagemagick))
              (org-create-formula-image
               body out-file org-format-latex-options in-buffer))
             ((string-suffix-p ".tikz" out-file)
	      (when (file-exists-p out-file) (delete-file out-file))
	      (with-temp-file out-file
	        (insert body)))
             ((and (not imagemagick)
                   (assoc extension org-latex-img-process))
              (with-temp-file tex-file
                (insert (concat
                         (org-latex-make-preamble
	                  (org-export-get-environment (org-export-get-backend 'latex))
	                  org-format-latex-header
	                  'snippet)
                         (if headers
			     (concat "\n"
				     (if (listp headers)
				         (mapconcat #'identity headers "\n")
				       headers) "\n")
		           "")
                         "\\begin{document}"
		         body
		         "\\end{document}")))
              (let ((tmp-pdf (org-babel-latex-tex-to-pdf tex-file)))
                (when (file-exists-p out-file) (delete-file out-file))
                (let* ((log-buf (get-buffer-create "*Org Babel LaTeX Output*"))
                       (err-msg "fix")
                       (img-out (org-compile-file
	                         tmp-pdf
                                 (cdr (assoc "svg" org-latex-img-process))
                                 extension err-msg log-buf)))
                  (shell-command (format "mv %s %s" img-out out-file)))))
	     ((and (or (string= "svg" extension)
		       (string= "html" extension))
	           (executable-find org-babel-latex-htlatex))
	      ;; TODO: this is a very different way of generating the
	      ;; frame latex document than in the pdf case.  Ideally, both
	      ;; would be unified.  This would prevent bugs creeping in
	      ;; such as the one fixed on Aug 16 2014 whereby :headers was
	      ;; not included in the SVG/HTML case.
	      (with-temp-file tex-file
	        (insert (concat
		         "\\documentclass[preview]{standalone}
\\def\\pgfsysdriver{pgfsys-tex4ht.def}
"
		         (mapconcat (lambda (pkg)
				      (concat "\\usepackage" pkg))
				    org-babel-latex-htlatex-packages
				    "\n")
		         (if headers
			     (concat "\n"
				     (if (listp headers)
				         (mapconcat #'identity headers "\n")
				       headers) "\n")
		           "")
		         "\\begin{document}"
		         body
		         "\\end{document}")))
	      (when (file-exists-p out-file) (delete-file out-file))
	      (let ((default-directory (file-name-directory tex-file)))
	        (shell-command (format "%s %s" org-babel-latex-htlatex tex-file)))
	      (cond
	       ((file-exists-p (concat (file-name-sans-extension tex-file) "-1.svg"))
	        (if (string-suffix-p ".svg" out-file)
		    (progn
		      (shell-command "pwd")
		      (shell-command (format "mv %s %s"
					     (concat (file-name-sans-extension tex-file) "-1.svg")
					     out-file)))
	          (error "SVG file produced but HTML file requested")))
	       ((file-exists-p (concat (file-name-sans-extension tex-file) ".html"))
	        (if (string-suffix-p ".html" out-file)
		    (shell-command "mv %s %s"
			           (concat (file-name-sans-extension tex-file)
				           ".html")
			           out-file)
	          (error "HTML file produced but SVG file requested")))))
	     ((or (string= "pdf" extension) imagemagick)
	      (with-temp-file tex-file
	        (require 'ox-latex)
	        (insert
	         (org-latex-guess-inputenc
	          (org-splice-latex-header
	           org-format-latex-header
	           (delq
		    nil
		    (mapcar
		     (lambda (el)
		       (unless (and (listp el) (string= "hyperref" (cadr el)))
		         el))
		     org-latex-default-packages-alist))
	           org-latex-packages-alist
	           nil))
	         (if fit "\n\\usepackage[active, tightpage]{preview}\n" "")
	         (if border (format "\\setlength{\\PreviewBorder}{%s}" border) "")
	         (if height (concat "\n" (format "\\pdfpageheight %s" height)) "")
	         (if width  (concat "\n" (format "\\pdfpagewidth %s" width))   "")
	         (if headers
		     (concat "\n"
			     (if (listp headers)
			         (mapconcat #'identity headers "\n")
			       headers) "\n")
	           "")
	         (if fit
		     (concat "\n\\begin{document}\n\\begin{preview}\n" body
			     "\n\\end{preview}\n\\end{document}\n")
	           (concat "\n\\begin{document}\n" body "\n\\end{document}\n"))))
              (when (file-exists-p out-file) (delete-file out-file))
	      (let ((transient-pdf-file (org-babel-latex-tex-to-pdf tex-file)))
	        (cond
	         ((string= "pdf" extension)
	          (rename-file transient-pdf-file out-file))
	         (imagemagick
	          (org-babel-latex-convert-pdf
	           transient-pdf-file out-file im-in-options im-out-options)
	          (when (file-exists-p transient-pdf-file)
		    (delete-file transient-pdf-file)))
	         (t
	          (error "Can not create %s files, please specify a .png or .pdf file or try the :imagemagick header argument"
		         extension))))))
            nil) ;; signal that output has already been written to file
        body))
```

What do people think? This gives you much more control over how the
latex is compiled and reuses existing functionality for previews.