org-latex-preview: Take advantage of dvisvgm3.2

* lisp/org-latex-preview.el (org-latex-preview--tex-styled,
org-latex-preview--dvisvgm-filter,
org-latex-preview--dvisvgm-version>=3.1,
org-latex-preview-process-alist,
org-latex-preview--dvisvgm3-minor-version): Take advantage of the new
--message flag of dvisvgm 3.2 to produce a more concise output.

lisp/org-latex-preview.el

@@ -39,6 +39,16 @@
 (defvar org-src-mode-hook nil)
 (defvar org-src--beg-marker nil)
 
+(defvar org-latex-preview--dvisvgm3-minor-version
+  (or (and (executable-find "dvisvgm")
+           (with-temp-buffer
+             (call-process "dvisvgm" nil t nil "--version")
+             (let ((ver (version-to-list
+                         (string-trim (buffer-string) "dvisvgm "))))
+               (and (= (car ver) 3) (cadr ver)))))
+      -1)
+  "The minor version of dvisvgm, if dvisvgm 3 is installed.  Otherwise -1.")
+
 (defgroup org-latex-preview nil
   "Options for generation of LaTeX previews in Org mode."
   :tag "Org LaTeX Preview"
@@ -111,7 +121,7 @@ All available processes and theirs documents can be found in
        ;; The --optimise, --clipjoin, and --relative flags cause dvisvgm to
        ;; do some extra work to tidy up the SVG output, but barely add to
        ;; the overall dvisvgm runtime (<1% increace, from testing).
-     :image-converter ("dvisvgm --page=1- --optimize --clipjoin --relative --no-fonts --bbox=preview -o %B-%%9p.svg %f"))
+       :image-converter determined-at-runtime)
       (imagemagick
        :programs ("pdflatex" "convert")
        :description "pdf > png"
@@ -176,6 +186,22 @@ Place-holders only used by `:image-converter':
   :type '(alist :tag "LaTeX to image backends"
           :value-type (plist)))
 
+;; This is a bit hacky, but since we can't include reference to the
+;; runtime value of `org-latex-preview--dvisvgm3-minor-version' in the
+;; default value of `org-latex-preview-process-alist', we have to
+;; resort to modifying the value at runtime like so.
+;; Theoretically only the "load" condition is needed, but some people seemed
+;; to have problems with this that are solved by adding "eval".
+(cl-eval-when (load eval)
+  (when-let ((dvisvgm (alist-get 'dvisvgm org-latex-preview-process-alist)))
+    (when (eq (plist-get dvisvgm :image-converter) 'determined-at-runtime)
+      (plist-put dvisvgm :image-converter
+                 (list
+                  (concat "dvisvgm --page=1- --optimize --clipjoin --relative --no-fonts"
+                          (if (>= org-latex-preview--dvisvgm3-minor-version 2)
+                              " -v3 --message='processing page {?pageno}: output written to {?svgfile}'" "")
+                          " --bbox=preview -o %B-%%9p.svg %f"))))))
+
 (defcustom org-latex-preview-compiler-command-map
   '(("pdflatex" . "latex")
     ("xelatex" . "xelatex -no-pdf")
@@ -2531,20 +2557,11 @@ fragments in EXTENDED-INFO."
       (org-latex-preview--place-images
        extended-info (nreverse fragments-to-show)))))
 
-(defvar org-latex-preview--dvisvgm-version>=3.1
-  (and (executable-find "dvisvgm")
-       (with-temp-buffer
-         (call-process "dvisvgm" nil t nil "--version")
-         (version<=
-          "3.1"
-          (string-trim (buffer-string) "dvisvgm "))))
-  "Whether dvisvgm >= 3.1 is installed.")
-
 (defun org-latex-preview--dvisvgm-filter (_proc _string extended-info)
   "Look for newly created images in the dvisvgm stdout buffer.
 Any matches found will be matched against the fragments recorded in
 EXTENDED-INFO, and displayed in the buffer."
-  (let ((dvisvgm-processing-re "^processing page \\([0-9]+\\)\n")
+  (let ((dvisvgm-processing-re "^processing page \\([0-9]+\\)[\n:]")
         (fragments (plist-get extended-info :fragments))
         page-marks fragments-to-show)
     (beginning-of-line)
@@ -2574,7 +2591,7 @@ EXTENDED-INFO, and displayed in the buffer."
       (setq page-marks (cdr page-marks)))
     (when fragments-to-show
       (setq fragments-to-show (nreverse fragments-to-show))
-      (if org-latex-preview--dvisvgm-version>=3.1
+      (if (>= org-latex-preview--dvisvgm3-minor-version 1)
           (mapc #'org-latex-preview--await-fragment-existance fragments-to-show)
         (mapc #'org-latex-preview--svg-make-fg-currentColor fragments-to-show))
       (org-latex-preview--place-images extended-info fragments-to-show))))
@@ -2927,7 +2944,7 @@ information for this run."
                     (and fg (format "\\color[rgb]{%s}" fg))
                     (and fg
                          (eq processing-type 'dvisvgm)
-                         org-latex-preview--dvisvgm-version>=3.1
+                         (>= org-latex-preview--dvisvgm3-minor-version 1)
                          "\\special{dvisvgm:currentcolor on}"))))
             (and num (format "\\setcounter{equation}{%d}" (1- num)))
             "%\n"