Re: Equation references in HTML export

[Thibault Marin <thibault.marin@gmx.com>]

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Hi, thanks for the review.  Please find attached an updated patch.

> I guess so. OTOH, I assume latex environments are always math
> environments. One can use LaTex export blocks for "regular" LaTeX.
I left the math check in the attached patch for now.  Please let me know
if you would like me to remove it.

> Nitpick: since this is a predicate, it should be named
> `org-html--math-environment-p'.
Done.

> Meanwhile, I think the implementation is a bit convoluted. What about
> the following?
>
>     (replace-regexp-in-string
>      "\\`[ \t]*\\\\begin{\\([^*]+?\\)}"
>      "\\1*"
>      (replace-regexp-in-string "^[ \t]*\\\\end{\\([^*]+?\\)}[ \r\t\n]*\\'"
>                                "\\1*"
>                                latex-frag nil nil 1)
>      nil nil 1)
Done.

> IMO, this doesn't deserve to be a function, you can just use something
> like this:
>
>     (if (org-string-nw-p label)
>         (replace-regexp-in-string "\\`.*"
>                                   (format "\\&\n\\\\label{%s}" label)
>                                   latex-frag)
>       latex-frag)
Done.

Thanks,

thibault


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From c600a62d67decf957e9170cf9f055915bdfae05a Mon Sep 17 00:00:00 2001
From: thibault <thibault.marin@gmx.com>
Date: Sun, 7 Jan 2018 03:04:39 -0600
Subject: [PATCH] ox-html.el: Add label and number to equations in HTML export

* lisp/ox-html.el (org-html--wrap-latex-environment): New function
wrapping the content of latex environments in HTML <div> tags, adding
"id" and equation number.
(org-html--math-environment-p): New function determining if a latex
environment is a math environment.
(org-html-latex-environment): Use `org-html--wrap-latex-environment' to
wrap equation in HTML container (non-MathJax modes).  Make latex
environment unnumbered when compiling equations to images.  Insert latex
label in environment in MathJax mode.
(org-html-link): Calculate equation number limiting counter to equation
environments.  Use eqref for link when using MathJax
(org-html--make-unlabelled-latex-environment): New function to convert
latex math environments to unnumbered versions (e.g. "equation" ->
"equation*").
---
 lisp/ox-html.el | 128 ++++++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 101 insertions(+), 27 deletions(-)

diff --git a/lisp/ox-html.el b/lisp/ox-html.el
index d242c613c..7b7d52141 100644
--- a/lisp/ox-html.el
+++ b/lisp/ox-html.el
@@ -430,6 +430,19 @@ for the JavaScript code in this tag.
   .footdef  { margin-bottom: 1em; }
   .figure { padding: 1em; }
   .figure p { text-align: center; }
+  .equation-container {
+    display: table;
+    text-align: center;
+    width: 100%;
+  }
+  .equation {
+    vertical-align: middle;
+  }
+  .equation-label {
+    display: table-cell;
+    text-align: right;
+    vertical-align: middle;
+  }
   .inlinetask {
     padding: 10px;
     border: 2px solid gray;
@@ -2823,26 +2836,75 @@ INFO is a plist containing export properties."
 			"Creating LaTeX Image..." nil processing-type)
       (buffer-string))))
 
+(defun org-html--wrap-latex-environment (contents info &optional caption label)
+  "Wrap CONTENTS string within appropriate environment for equations.
+INFO is a plist used as a communication channel.  When optional
+arguments CAPTION and LABEL are given, use them for caption and
+\"id\" attribute."
+  (format "\n<div%s class=\"equation-container\">\n%s%s\n</div>"
+          ;; ID.
+          (if (org-string-nw-p label) (format " id=\"%s\"" label) "")
+          ;; Contents.
+          (format "<span class=\"equation\">\n%s\n</span>" contents)
+          ;; Caption.
+          (if (not (org-string-nw-p caption)) ""
+            (format "\n<span class=\"equation-label\">\n%s\n</span>"
+                    caption))))
+
+(defun org-html--math-environment-p (element &optional info)
+  "Non-nil when ELEMENT is a LaTeX math environment.
+Math environments match the regular expression defined in
+`org-latex-math-environments-re'.
+INFO is a plist used as a communication channel.  This function
+is meant to be used as a predicate for `org-export-get-ordinal' or
+a value to `org-html-standalone-image-predicate'."
+  (string-match-p org-latex-math-environments-re
+                  (org-element-property :value element)))
+
+(defun org-html--make-unlabelled-latex-environment (latex-frag)
+  "Change environment in LATEX-FRAG to an unnumbered environment.
+For instance, change an 'equation' environment to 'equation*'."
+  (replace-regexp-in-string
+   "\\`[ \t]*\\\\begin{\\([^*]+?\\)}"
+   "\\1*"
+   (replace-regexp-in-string "^[ \t]*\\\\end{\\([^*]+?\\)}[ \r\t\n]*\\'"
+			     "\\1*"
+			     latex-frag nil nil 1)
+   nil nil 1))
+
 (defun org-html-latex-environment (latex-environment _contents info)
   "Transcode a LATEX-ENVIRONMENT element from Org to HTML.
 CONTENTS is nil.  INFO is a plist holding contextual information."
   (let ((processing-type (plist-get info :with-latex))
 	(latex-frag (org-remove-indentation
 		     (org-element-property :value latex-environment)))
-	(attributes (org-export-read-attribute :attr_html latex-environment)))
+        (attributes (org-export-read-attribute :attr_html latex-environment))
+        (label (and (org-element-property :name latex-environment)
+                    (org-export-get-reference latex-environment info)))
+        (caption (number-to-string
+                  (org-export-get-ordinal
+                   latex-environment info nil
+                   #'org-html--math-environment-p))))
     (cond
      ((memq processing-type '(t mathjax))
-      (org-html-format-latex latex-frag 'mathjax info))
+      (org-html-format-latex
+       (if (org-string-nw-p label)
+	   (replace-regexp-in-string "\\`.*"
+				     (format "\\&\n\\\\label{%s}" label)
+				     latex-frag)
+	 latex-frag)
+       'mathjax info))
      ((assq processing-type org-preview-latex-process-alist)
       (let ((formula-link
-	     (org-html-format-latex latex-frag processing-type info)))
-	(when (and formula-link (string-match "file:\\([^]]*\\)" formula-link))
-	  ;; Do not provide a caption or a name to be consistent with
-	  ;; `mathjax' handling.
-	  (org-html--wrap-image
-	   (org-html--format-image
-	    (match-string 1 formula-link) attributes info) info))))
-     (t latex-frag))))
+             (org-html-format-latex
+              (org-html--make-unlabelled-latex-environment latex-frag)
+              processing-type info)))
+        (when (and formula-link (string-match "file:\\([^]]*\\)" formula-link))
+          (org-html--wrap-latex-environment
+           (org-html--format-image
+            (match-string 1 formula-link) attributes info)
+           info caption label))))
+     (t (org-html--wrap-latex-environment latex-frag info caption label)))))
 
 ;;;; Latex Fragment
 
@@ -3062,23 +3124,35 @@ INFO is a plist holding contextual information.  See
 	     (format "<a href=\"#%s\"%s>%s</a>" href attributes desc)))
 	  ;; Fuzzy link points to a target or an element.
 	  (_
-	   (let* ((ref (org-export-get-reference destination info))
-		  (org-html-standalone-image-predicate
-		   #'org-html--has-caption-p)
-		  (number (cond
-			   (desc nil)
-			   ((org-html-standalone-image-p destination info)
-			    (org-export-get-ordinal
-			     (org-element-map destination 'link
-			       #'identity info t)
-			     info 'link 'org-html-standalone-image-p))
-			   (t (org-export-get-ordinal
-			       destination info nil 'org-html--has-caption-p))))
-		  (desc (cond (desc)
-			      ((not number) "No description for this link")
-			      ((numberp number) (number-to-string number))
-			      (t (mapconcat #'number-to-string number ".")))))
-	     (format "<a href=\"#%s\"%s>%s</a>" ref attributes desc))))))
+           (if (and destination
+                    (memq (plist-get info :with-latex) '(mathjax t))
+                    (eq 'latex-environment (org-element-type destination))
+                    (eq 'math (org-latex--environment-type destination)))
+               ;; Caption and labels are introduced within LaTeX environment. Use
+               ;; "eqref" macro to refer to those in the document.
+               (format "\\eqref{%s}"
+                       (org-export-get-reference destination info))
+             (let* ((ref (org-export-get-reference destination info))
+                    (org-html-standalone-image-predicate
+                     #'org-html--has-caption-p)
+                    (ordinal-counter-predicate
+                     (if (string= (car destination) "latex-environment")
+                         #'org-html--math-environment-p
+                       #'org-html--has-caption-p))
+                    (number (cond
+                             (desc nil)
+                             ((org-html-standalone-image-p destination info)
+                              (org-export-get-ordinal
+                               (org-element-map destination 'link
+                                 #'identity info t)
+                               info 'link 'org-html-standalone-image-p))
+                             (t (org-export-get-ordinal
+                                 destination info nil ordinal-counter-predicate))))
+                    (desc (cond (desc)
+                                ((not number) "No description for this link")
+                                ((numberp number) (number-to-string number))
+                                (t (mapconcat #'number-to-string number ".")))))
+               (format "<a href=\"#%s\"%s>%s</a>" ref attributes desc)))))))
      ;; Coderef: replace link with the reference name or the
      ;; equivalent line number.
      ((string= type "coderef")
-- 
2.15.1