Re: Use cases for post-redisplay hooks

["Clément Pit--Claudel" <clement.pit@gmail.com>]

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But I meant ­— can't you update this flag yourself, and do at most one recalculation per command loop?

On 2016-07-07 13:53, Keith David Bershatsky wrote:
> Yes, a `needs-recalculation` flag would be very useful -- i.e., when the values for `window-start` and `window-end` are correct and not going to change, then run the Lisp function (attached to the hook) that depends upon those values being correct.  A counter, however, may not be a reliable indicator of the above test.
> 
> [My assumption is that overlays could be placed before the screen visually refreshes, so that the overlays are visually present when redisplay finishes.]
> 
> Keith
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> At Thu, 7 Jul 2016 12:08:09 -0400,
> Clément Pit--Claudel wrote:
>>
>> On 2016-07-04 18:50, Keith David Bershatsky wrote:
>>> The reason I mentioned the `window-scroll-functions` hook was an
>>> assumption (on my part) that Clément had initially categorized my
>>> potential usage of the proposed `post-redisplay-hook` as only
>>> relating to scrolling.  I just wanted to clarify / differentiate my
>>> proposed use case as needing `window-start` and `window-end` each
>>> command loop.
>>
>> IIUC then the post-redisplay-hook thing wouldn't work very nicely: in general, it's going to run more often than once per command loop cycle.
>>
>>> With respect to the hook running more than once each command loop, it
>>> is only a problem for me because my calculations are costly time-wise
>>> (e.g., `vertical-motion').  So, I only want to do it one time each
>>> command loop.
>>
>> Would registering a post-command hook and incrementing a counter in there help? You would then predicate your costly calculations on the value of that counter having changed since the last time the calculations ran.
>>
>> Even simpler: in a pre/post-command hook switch a `needs-recalculation' flag to t, and after completing the calculations (from whichever other hook you're using for them) switch `needs-recalculation' to nil. If the function doing the calculations is called when `needs-recalculation' is nil, then can exit immediately.
>>
>> Or is there something more complex that I'm missing?
>>
>> Clément.
>>
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