bug#22404: 25.1.50; Forcing `window-scroll-functions` to run.

[Eli Zaretskii]

> Date: Mon, 18 Jan 2016 21:49:40 -0800
> From: Keith David Bershatsky <esq@lawlist.com>
> 
> As a feature request, please consider adding an alternative method to force 
> the `window-scroll-functions` hook to run -- but NOT more than it would 
> normally run. [In other words, it shouldn't run 3 times.]  I only found 
> `(set-window-buffer (selected-window) (current-buffer))` as a viable means to 
> achieve this goal.  `run-window-scroll-functions` runs immediately and is not 
> a viable substitute for this feature request.  Some users may not wish to 
> `set-window-buffer` or run the `window-configuration-change-hook` to achieve 
> this feature request.
> 
> In my particular use case, I want to run a custom function only one time per 
> command loop that is dependent upon the new `window-start` and `window-end`, 
> which is only reliably available to the user after the `post-command-hook` 
> has run its course.  My function is too costly time-wise to run more than 
> once each command loop.  I have tried, to no avail, to come up with a test to 
> ascertain with 100% accuracy (from the `post-command-hook`) to guess whether 
> the `window-scroll-functions` hook will run and/or whether it will run more 
> than one time (e.g., when cursor/point is partially visible).  I played 
> around with `(pos-visible-in-window-p nil nil t)` and whether it returned a 
> length of 0, 2 or 6 -- however, from the `post-command-hook`, that is 
> insufficient to ascertain with 100% accuracy whether the 
> `window-scroll-functions` hook will run once or twice or not at all.  The 
> solution, I believe, is to force the `window-scroll-functions` hook to run 
> during every redisplay -- but not more than it would normally run.
> 
> In other words, I want the `window-scroll-functions` hook to run every 
> command loop when my custom minor-mode is active -- or twice if point/cursor 
> is only partially visible (at the bottom of the window) and needs to be moved 
> up a smidgen by redisplay.
> 
> Background:  my custom function is a cross-hairs created with overlays that 
> works with `word-wrap` -- the vertical line is XPM that matches the character 
> and color underneath.

Can you please tell more details about the problem you have?  I;ve
read this description several times, and couldn't figure out why are
you having problems.

For example, why can't you run your function from the
post-command-hook directly?  If you want it to run after all the hook
functions finished, you can use the APPEND argument to add-hook,
right?

Or if the above somehow doesn't work, what about pre-command-hook?

And those are just 2 random thoughts that went through my head while I
was reading your request.

Thanks.