Re: emacs rendering comparisson between emacs23 and emacs26.3

[Stefan Monnier]

>> 16s in one case a "10 seconds freeze": it sounds to me like you *do*
>> reproduce the problem.
> Not really.  In the 16s case redisplay kicks in and displays the buffer
> 250 times.  In the 10s case redisplay stops after five times.

Yes, but the underlying problem remains: it takes 10-16s to do the work,
so if the corresponding input events come in over a period shorter than
10-16s Emacs won't be able to keep up.

>> The only difference is that with actual keyboard input pending the
>> redisplay is partly prevented which is what you perceive as "freeze",
>> but the real problem is the time it takes.
> What does get fontified when redisplay freezes?

The text gets fontified by the scrolling routine because the size of the
text depends on the fontification, so correct scrolling needs to fontify
the text before it can compute the destination of the scroll.

That's where `fast-but-imprecise-scrolling` comes into play.


        Stefan