Re: Use cases for post-redisplay hooks

[Keith David Bershatsky]

With my limited computer skills, I was not able to find the "sweet spot" in the 
redisplay code where I knew for sure that `window-start' and `window-end' were 
always going to be correct such that I could easily set a hypothetical 
`needs-recalculation' flag to `nil'.  When I tried applying overlays too late 
in time in the redisplay cycle, there were visual problems updating the screen.

With my custom `window-start-end-hook' (with accepts a function with arguments 
for `window-start' and `window-end'), I use a test (built into the C code) to 
see whether point is fully visible before I run the Lisp function attached to 
the hook.  However, it assumes that `make-cursor-line-fully-visible' remains 
set at the default value of `t'.  I use `(setq scroll-conservatively 101)'.  On 
my todo-list, is to figure out how to incorporate a test (akin to `needs 
recalculation') for when `make-cursor-line-fully-visible' is set to `nil'.  
Essentially, redisplay does less work when `make-cursor-line-fully-visible' is 
`nil'.  I've been using a custom build of Emacs with the 
`window-start-end-hook' since shortly after generating Emacs feature request 
22404.

Keith

At Thu, 7 Jul 2016 15:44:13 -0400,
Clément Pit--Claudel wrote:
> 
> But I meant ­— can't you update this flag yourself, and do at most one 
> recalculation per command loop?