Re: Scrolling commands and skipping redisplay, was: Re: emacs rendering comparisson between emacs23 and emacs26.3

[Stefan Monnier]

> Thanks. I tried it (and mentioned in the parent thread), but it seems like
> in addition to the downsides of f-b-i-s (imprecise scrolling, which
> apparently makes it a bad candidate for default behavior) it adds some 
> extra flickering from time to time (I figured because some redisplays
> occurred before the idle timer had the chance to run). It's not as 
> obvious in an 'emacs -Q' session, but with my custom config it's more
> apparent. And that flickering occurs the most while I'm flooring C-v.

I think the flickering is the direct effect of the defer'd jit-lock: you
first see the non-jit-lock'd text and only after that the idle timer
runs jit-lock and updates the display accordingly.

> Is it possible that the conditions for skipping redisplay might return
> false while input-pending-p returns t?

Very much so, yes: the tests are sufficiently different and the possible
circumstances sufficiently varied that it's almost unavoidable.

E.g. usually the redisplay is skipped based on the presence of input at
the *beginning* of the command, whereas the `jit-lock-defer-time` thingy
samples the input later, when jit-lock is called.


        Stefan