Re: master 4b5d04b: Use new macro debounce-reduce to make mouse scaling of images more responsive

[Juri Linkov <juri@linkov.net>]

>>>>     * lisp/emacs-lisp/timer.el (debounce, debounce-reduce): New macros.
>>> Please use proper prefixes for those names.
>> Maybe timer-debounce and timer-debounce-reduce.
>
> I guess so, tho now that I looked at it I have other questions/comments:
>
> - I don't see `debounce` used anywhere.  Do we need it?

I prepared a patch that uses `debounce`, but then waited until resolving
the question of prefixes.  But now I installed the patch in b31a966e88
and will add the prefixes afterwards.

> - Why is `debounce-reduce` a macro rather than a function?

In its initial versions that used `body` it needed to be a macro,
but now it can be a function indeed.

> - What is the advantage of wrapping a `debounce-reduce` around
>   `image--change-size` instead of doing something like:
>
>     (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")
>       ;; Wait for a bit of idle-time before actually performing the change,
>       ;; so as to batch together sequences of closely consecutive size changes.
>       (run-with-idle-timer 0.3 nil
>                            #'image--change-size
>                            (if n
>                                (- 1 (/ (prefix-numeric-value n) 10.0))
>                              0.8)))

This version doesn't discard a sequence of consecutive calls
where every call is a costly operation.  For example, on slow hardware
every image resize takes about 1 sec.  Thus when mouse-wheel
generates 5 events, this version will wait for the next idle time,
then will resize the image sequentially 5 times during 5 seconds.

Whereas `debounce-reduce` accumulates all mouse wheel events, and then
calls only one resize operation with the collected scaling factor.