From efb637131528ccb5edad52beea131f2255bb1cda Mon Sep 17 00:00:00 2001
From: Karthik Chikmagalur <karthikchikmagalur@gmail.com>
Date: Sat, 15 Apr 2023 23:49:12 -0700
Subject: [PATCH] org-latex-preview: Don't fully reset overlay state

* lisp/org-latex-preview.el (org-latex-preview--ensure-overlay,
org-latex-preview--update-overlay): When ensuring a preview overlay
exists, do not fully reset the state of the overlay, such as the
stored image spec, the flag that checks if the preview is open, etc.
Persisting prior state is required for the "live" preview
feature (introduced in the following commits) to function.  Similarly,
if "live" previewing a LaTeX element that has an overlay attached, do
not set the overlay face or error display indicator(s).
---
 lisp/org-latex-preview.el | 54 ++++++++++++++++++++++-----------------
 1 file changed, 30 insertions(+), 24 deletions(-)

diff --git a/lisp/org-latex-preview.el b/lisp/org-latex-preview.el
index a845d224a..e221432d4 100644
--- a/lisp/org-latex-preview.el
+++ b/lisp/org-latex-preview.el
@@ -392,15 +392,20 @@ the image.")
           (overlay-put ov 'face nil)
           (overlay-put ov 'help-echo nil)     ;tooltip error display
           (overlay-put ov 'before-string nil) ;error fringe marker
-          (overlay-put ov 'hidden-face nil)   ;(re)store svg face
-          ;; Do not set the display property of preview image
+          ;; (overlay-put ov 'hidden-face nil)   ;(re)store svg face
+          ;; We do not set the display property of preview image
           ;; overlays to nil when ensuring that an overlay exists.
           ;; This causes flicker during regeneration as the the
           ;; underlying text is shown and then replaced with the new
           ;; image.
-          (overlay-put ov 'preview-image nil) ;(re)store image spec
+          ;;
+          ;; We also do not reset the image spec stored in the
+          ;; `preview-image' property, or the state of the preview
+          ;; stored in the `view-text' property, as persisting the
+          ;; state of an already existing overlay is required for live
+          ;; previews.
           (overlay-put ov 'preview-state nil) ;is fragment modified?
-          (overlay-put ov 'view-text nil))))
+          )))
     (unless ov
       (setq ov (make-overlay beg end nil 'front-advance))
       (overlay-put ov 'org-overlay-type 'org-latex-overlay)
@@ -469,28 +474,29 @@ overlay face is set to `org-latex-preview-processing-face'."
                                  (round (* 100 (- 1 (/ (max 0.0 (- depth 0.02))
                                                        height))))
                                'center)))))
+    (overlay-put ov 'preview-image image-display)
+    (cond
+       ((eq image-type 'svg)
+        (overlay-put
+         ov 'hidden-face
+         (or (and errors 'error)
+             (org-latex-preview--face-around
+              (overlay-start ov) (overlay-end ov)))))
+       (errors
+        (overlay-put
+         ov 'before-string
+         (propertize "!" 'display
+                     `(left-fringe exclamation-mark error)))))
     (when org-latex-preview-processing-indicator
       (org-latex-preview--indicate-processing ov))
-    ;; This is a temporary measure until a more sophisticated
-    ;; interface for errors is available in Org.
-    (when (and errors tooltip-mode)
-      (overlay-put ov 'help-echo errors))
-    (when image-display
-      (overlay-put ov 'display image-display)
-      (overlay-put ov 'preview-image image-display))
-    (cond
-     ((eq image-type 'svg)
-      (overlay-put
-       ov 'face
-       (or (and errors 'error)
-           (org-latex-preview--face-around
-            (overlay-start ov) (overlay-end ov)))))
-     (errors
-      (overlay-put
-       ov 'before-string
-       (propertize "!" 'display
-                   `(left-fringe exclamation-mark error))))))
-      (run-hook-with-args 'org-latex-preview-update-overlay-functions ov))
+    (unless (overlay-get ov 'view-text) ;Live previewing this element, update in background
+      ;; This is a temporary measure until a more sophisticated
+      ;; interface for errors is available in Org.
+      (when (and errors tooltip-mode)
+        (overlay-put ov 'help-echo errors))
+      (when image-display (overlay-put ov 'display image-display))
+      (overlay-put ov 'face (overlay-get ov 'hidden-face)))
+    (run-hook-with-args 'org-latex-preview-update-overlay-functions ov)))
 
 (defun org-latex-preview--face-around (start end)
   "Return the relevant face symbol around the region START to END.