Use new macro debounce-reduce to make mouse scaling of images more responsive

* lisp/emacs-lisp/timer.el (debounce, debounce-reduce): New macros.

* lisp/image.el (image-increase-size, image-decrease-size):
Use funcall to call image--change-size-function.
(image--change-size-function): Move code from defun of
image--change-size to defvar that has the value of lambda
returned from debounce-reduce.  (Bug#38187)

1 files changed, 5 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 3bf4c81014b..819637b79fc 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -2796,6 +2796,11 @@ doing computations on a decoded time structure), 'make-decoded-time'
 filled out), and 'encoded-time-set-defaults' (which fills in nil
 elements as if it's midnight January 1st, 1970) have been added.
 
+** New macros 'debounce' and 'debounce-reduce' postpone function call
+until after specified time have elapsed since the last time it was invoked.
+This improves performance of processing events occurring rapidly
+in quick succession.
+
 ** 'define-minor-mode' automatically documents the meaning of ARG.
 
 +++