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 > > ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; > > 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. >> >> [2 OpenPGP digital signature ] >