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Re: Unfreezing the display during auto-repeated scrolling. Simpler appro

From: Alan Mackenzie
Subject: Re: Unfreezing the display during auto-repeated scrolling. Simpler approach.
Date: Sun, 23 Nov 2014 22:04:41 +0000
User-agent: Mutt/1.5.21 (2010-09-15)

Hello, Tassilo.

On Sun, Nov 23, 2014 at 08:44:39PM +0100, Tassilo Horn wrote:
> Alan Mackenzie <address@hidden> writes:

> Hi Alan,

> > To see the effect, make your window as large as possible (mine was 66
> > lines deep) and try with a file like .../src/xdisp.c.  Toggle
> > font-lock-mode off and on between each try.  If you still don't see any
> > difference, then your machine is powerful enough not to need the feature.

> Oh, indeed.  My machine is pretty fast at least for a laptop, but when
> holding C-v the display freezes very quickly as you say.  With
> `use-default-face-for-fast-scrolling' I don't get such freezes, so this
> looks like a very good feature to me (2nd best after "make the display
> engine faster").

It's CC Mode's fontification, rather than the display engine, which is
slow here.  But in a large window, even Emacs Lisp Mode can only just
keep up: On my 2.6 GHz Athlon II, with a 66 line window, and the keyboard
auto-repeating every 0.024s, fontifying and displaying a screen took
~0.018s.  There's not a lot of spare time for fancier fontification.

> But still I think the variable's name is a bit misleading.  I expected
> to see the text that scrolls by black on white, i.e., using the default
> face similar to having `jit-lock-defer-time' set to some non-nil value.
> But instead the text that scrolls by and is visible is fontified using
> the normal font-lock faces.

:-).  I had quite some trouble coming up with a name for the option.
Something like
`assume-default-face-for-nondisplayed-screens-in-scrolling' would be more
accurate, but a bit of a mouthful.  If you've any suggestions for
improvement, post them!

> Bye,
> Tassilo

Alan Mackenzie (Nuremberg, Germany).

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