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Re: Use cases for post-redisplay hooks

From: Clément Pit--Claudel
Subject: Re: Use cases for post-redisplay hooks
Date: Thu, 7 Jul 2016 12:08:09 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.8.0

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 

Or is there something more complex that I'm missing?


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