Implement highlight a duration when preview line changed (#16)

* highlight a duration when preview line changed

* goto-line-preview-hl-duration accept nil

---------

Co-authored-by: LiuYinCarl <bearcarl@qq.com>

README.md

@@ -31,6 +31,18 @@ Or you can bind it globally to replace `goto-line`:
 (global-set-key [remap goto-line] 'goto-line-preview)
 ```
 
+## Change hightlight color or duration
+
+```el
+;; Highlight 1.5 seconds when change preview line
+(setq goto-line-preview-hl-duration 1.5)
+
+;; Change highlight background color to white
+(setq goto-line-preview-hl-color "white")
+```
+
+If you want to close highlight, set `goto-line-preview-hl-duration` to 0 or `nil`.
+
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goto-line-preview.el

@@ -48,6 +48,16 @@
   :group 'goto-line-preview
   :type 'hook)
 
+(defcustom goto-line-preview-hl-duration 1
+  "Duration of highlight when change preview line."
+  :group 'goto-line-preview
+  :type 'integer)
+
+(defcustom goto-line-preview-hl-color "DimGray"
+  "Background color of highlight when change preview line."
+  :group 'goto-line-preview
+  :type 'string)
+
 (defvar goto-line-preview--prev-window nil
   "Record down the previous window before we do preivew display.")
 
@@ -57,12 +67,21 @@
 (defvar goto-line-preview--relative-p nil
   "Flag to see if this command relative.")
 
+(defun goto-line-preview--highlight ()
+  "Keep highlight for a fixed time."
+  (if goto-line-preview-hl-duration
+      (let ((overlay (make-overlay (line-beginning-position) (line-end-position))))
+        (overlay-put overlay 'face `(:background ,goto-line-preview-hl-color))
+        (sit-for goto-line-preview-hl-duration)
+        (delete-overlay overlay))))
+
 (defun goto-line-preview--do (line-num)
   "Do goto LINE-NUM."
   (save-selected-window
     (select-window goto-line-preview--prev-window)
     (goto-char (point-min))
-    (forward-line (1- line-num))))
+    (forward-line (1- line-num))
+    (goto-line-preview--highlight)))
 
 (defun goto-line-preview--do-preview ()
   "Do the goto line preview action."