Use run-with-idle-timer instead of debounce for responsive image scaling.

* lisp/emacs-lisp/timer.el (debounce, debounce-reduce): Revert macro addition.
https://lists.gnu.org/archive/html/emacs-devel/2019-11/msg01133.html

* lisp/image.el (image-increase-size, image-decrease-size):
Use run-with-idle-timer.
(image--change-size): Rename back from image--change-size-function.

* lisp/image-mode.el (image-mode--setup-mode): Remove hooks
window-size-change-functions and window-selection-change-functions (bug#32672)
(image-fit-to-window): Rename from image--window-change-function.
(image--window-state-change): Rename from image--window-change.
Use run-with-idle-timer.

3 files changed, 54 insertions, 85 deletions

diff --git a/lisp/emacs-lisp/timer.el b/lisp/emacs-lisp/timer.el
index 5fdf9a426a7..561cc70078f 100644
--- a/lisp/emacs-lisp/timer.el
+++ b/lisp/emacs-lisp/timer.el
@@ -488,50 +488,6 @@ The argument should be a value previously returned by `with-timeout-suspend'."
 If the user does not answer after SECONDS seconds, return DEFAULT-VALUE."
   (with-timeout (seconds default-value)
     (y-or-n-p prompt)))
-
-(defmacro debounce (secs function)
-  "Call FUNCTION after SECS seconds have elapsed.
-Postpone FUNCTION call until after SECS seconds have elapsed since the
-last time it was invoked.  On consecutive calls within the interval of
-SECS seconds, cancel all previous calls that occur rapidly in quick succession,
-and execute only the last call.  This improves performance of event processing."
-  (declare (indent 1) (debug t))
-  (let ((timer-sym (make-symbol "timer")))
-    `(let (,timer-sym)
-       (lambda (&rest args)
-         (when (timerp ,timer-sym)
-           (cancel-timer ,timer-sym))
-         (setq ,timer-sym
-               (run-with-timer
-                ,secs nil (lambda ()
-                            (apply ,function args))))))))
-
-(defmacro debounce-reduce (secs initial-state state-function function)
-  "Call FUNCTION after SECS seconds have elapsed.
-Postpone FUNCTION call until after SECS seconds have elapsed since the
-last time it was invoked.  On consecutive calls within the interval of
-SECS seconds, cancel all previous calls that occur rapidly in quick succession,
-and execute only the last call.  This improves performance of event processing.
-
-STATE-FUNCTION can be used to accumulate the state on consecutive calls
-starting with the value of INITIAL-STATE, and then execute the last call
-with the collected state value."
-  (declare (indent 1) (debug t))
-  (let ((timer-sym (make-symbol "timer"))
-        (state-sym (make-symbol "state")))
-    `(let (,timer-sym (,state-sym ,initial-state))
-       (lambda (&rest args)
-         (setq ,state-sym (apply ,state-function ,state-sym args))
-         (when (timerp ,timer-sym)
-           (cancel-timer ,timer-sym))
-         (setq ,timer-sym
-               (run-with-timer
-                ,secs nil (lambda ()
-                            (apply ,function (if (listp ,state-sym)
-                                                 ,state-sym
-                                               (list ,state-sym)))
-                            (setq ,state-sym ,initial-state))))))))
-
 
 (defconst timer-duration-words
   (list (cons "microsec" 0.000001)
diff --git a/lisp/image-mode.el b/lisp/image-mode.el
index 09d7828047e..b9ba376cafc 100644
--- a/lisp/image-mode.el
+++ b/lisp/image-mode.el
@@ -599,9 +599,7 @@ Key bindings:
 
   (add-hook 'change-major-mode-hook #'image-toggle-display-text nil t)
   (add-hook 'after-revert-hook #'image-after-revert-hook nil t)
-  (add-hook 'window-size-change-functions #'image--window-change nil t)
-  (add-hook 'window-state-change-functions #'image--window-change nil t)
-  (add-hook 'window-selection-change-functions #'image--window-change nil t)
+  (add-hook 'window-state-change-functions #'image--window-state-change nil t)
 
   (run-mode-hooks 'image-mode-hook)
   (let ((image (image-get-display-property))
@@ -860,26 +858,31 @@ Otherwise, display the image by calling `image-mode'."
           (get-buffer-window-list (current-buffer) 'nomini 'visible))
     (image-toggle-display-image)))
 
-(defvar image--window-change-function
-  (debounce 1.0
-    (lambda (window)
-      (when (window-live-p window)
-        (with-current-buffer (window-buffer)
-          (when (derived-mode-p 'image-mode)
-            (let ((spec (image-get-display-property)))
-              (when (eq (car-safe spec) 'image)
-                (let* ((image-width  (plist-get (cdr spec) :max-width))
-                       (image-height (plist-get (cdr spec) :max-height))
-                       (edges (window-inside-pixel-edges window))
-                       (window-width  (- (nth 2 edges) (nth 0 edges)))
-                       (window-height (- (nth 3 edges) (nth 1 edges))))
-                  (when (and image-width image-height
-                             (or (not (= image-width  window-width))
-                                 (not (= image-height window-height))))
-                    (image-toggle-display-image)))))))))))
-
-(defun image--window-change (window)
-  (funcall image--window-change-function window))
+(defun image--window-state-change (window)
+  ;; Wait for a bit of idle-time before actually performing the change,
+  ;; so as to batch together sequences of closely consecutive size changes.
+  ;; `image-fit-to-window' just changes one value in a plist.  The actual
+  ;; image resizing happens later during redisplay.  So if those
+  ;; consecutive calls happen without any redisplay between them,
+  ;; the costly operation of image resizing should happen only once.
+  (run-with-idle-timer 1 nil #'image-fit-to-window window))
+
+(defun image-fit-to-window (window)
+  "Adjust size of image to display it exactly in WINDOW boundaries."
+  (when (window-live-p window)
+    (with-current-buffer (window-buffer)
+      (when (derived-mode-p 'image-mode)
+        (let ((spec (image-get-display-property)))
+          (when (eq (car-safe spec) 'image)
+            (let* ((image-width  (plist-get (cdr spec) :max-width))
+                   (image-height (plist-get (cdr spec) :max-height))
+                   (edges (window-inside-pixel-edges window))
+                   (window-width  (- (nth 2 edges) (nth 0 edges)))
+                   (window-height (- (nth 3 edges) (nth 1 edges))))
+              (when (and image-width image-height
+                         (or (not (= image-width  window-width))
+                             (not (= image-height window-height))))
+                (image-toggle-display-image)))))))))
 
 
 ;;; Animated images
diff --git a/lisp/image.el b/lisp/image.el
index c4304782327..f4ed4e79fc0 100644
--- a/lisp/image.el
+++ b/lisp/image.el
@@ -1017,20 +1017,34 @@ has no effect."
 If N is 3, then the image size will be increased by 30%.  The
 default is 20%."
   (interactive "P")
-  (funcall image--change-size-function
-           (if n
-               (1+ (/ (prefix-numeric-value n) 10.0))
-             1.2)))
+  ;; Wait for a bit of idle-time before actually performing the change,
+  ;; so as to batch together sequences of closely consecutive size changes.
+  ;; `image--change-size' just changes one value in a plist.  The actual
+  ;; image resizing happens later during redisplay.  So if those
+  ;; consecutive calls happen without any redisplay between them,
+  ;; the costly operation of image resizing should happen only once.
+  (run-with-idle-timer 0.3 nil
+                       #'image--change-size
+                       (if n
+                           (1+ (/ (prefix-numeric-value n) 10.0))
+                         1.2)))
 
 (defun image-decrease-size (&optional n)
   "Decrease the image size by a factor of N.
 If N is 3, then the image size will be decreased by 30%.  The
 default is 20%."
   (interactive "P")
-  (funcall image--change-size-function
-           (if n
-               (- 1 (/ (prefix-numeric-value n) 10.0))
-             0.8)))
+  ;; Wait for a bit of idle-time before actually performing the change,
+  ;; so as to batch together sequences of closely consecutive size changes.
+  ;; `image--change-size' just changes one value in a plist.  The actual
+  ;; image resizing happens later during redisplay.  So if those
+  ;; consecutive calls happen without any redisplay between them,
+  ;; the costly operation of image resizing should happen only once.
+  (run-with-idle-timer 0.3 nil
+                       #'image--change-size
+                       (if n
+                           (- 1 (/ (prefix-numeric-value n) 10.0))
+                         0.8)))
 
 (defun image-mouse-increase-size (&optional event)
   "Increase the image size using the mouse."
@@ -1065,16 +1079,12 @@ default is 20%."
       (plist-put (cdr image) :type 'imagemagick))
     image))
 
-(defvar image--change-size-function
-  (debounce-reduce 0.3 1
-    (lambda (state factor)
-      (* state factor))
-    (lambda (factor)
-      (let* ((image (image--get-imagemagick-and-warn))
-             (new-image (image--image-without-parameters image))
-             (scale (image--current-scaling image new-image)))
-        (setcdr image (cdr new-image))
-        (plist-put (cdr image) :scale (* scale factor))))))
+(defun image--change-size (factor)
+  (let* ((image (image--get-imagemagick-and-warn))
+         (new-image (image--image-without-parameters image))
+         (scale (image--current-scaling image new-image)))
+    (setcdr image (cdr new-image))
+    (plist-put (cdr image) :scale (* scale factor))))
 
 (defun image--image-without-parameters (image)
   (cons (pop image)