Re: Use cases for post-redisplay hooks

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

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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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