Re: Why emacs rendering is slow when encountering long lines?

[Jules Colding]

On Oct 21, 2013, at 5:00 AM, Eli Zaretskii <eliz@gnu.org> wrote:

>> Date: Sun, 20 Oct 2013 19:08:51 -0700 (PDT)
>> From: Jiaxin Cao <jiaxin.cao@gmail.com>
>> Injection-Date: Mon, 21 Oct 2013 02:08:52 +0000
>> 
>> Let me provide more information about this. To reproduce the scenario, just 
>> create a line containing about 450 chars, and copy the line 10000 times.
> 
>> 
>> Based on the results, I guess the scroll-down is the bottleneck of the 
>> scrolling performance.
> 
> Your conclusion is wrong.  You assume that scroll-down is just that,
> but it isn't.  It invokes the display engine to know where to start
> the next/previous screenful.  Try to think of an algorithm to
> determine that, when the buffer might have different fonts, and I
> think you will see why.

I have a file here:

https://github.com/colding/MercuryFIX/blob/master/applib/fixio_tests/check_fixio.cpp

which has an extremely long word (one font, all caps) at line 213. As soon as 
scrolling down comes within 2-3 lines distance, everything stops for a second 
or two.

Just a datapoint...


-- 
  jules