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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 10:40:38 +0000
User-agent: Mutt/1.5.21 (2010-09-15)

Hello, Tassilo.

On Sun, Nov 23, 2014 at 10:51:43AM +0100, Tassilo Horn wrote:
> Alan Mackenzie <address@hidden> writes:

> Hi Alan,

> > Just a short summary of this change: introduce a new user option, off
> > by default, which suppresses fontification (by binding
> > fontification-functions to nil) when the user scrolls by whole
> > screens.

> Just as a data point: i think I'd have a use for such a feature even
> with a pretty recent machine.

> But I've applied your patch and run "make", fired up a new emacs and set
> `use-default-face-for-fast-scrolling' to t, then found a large file and
> pressed and held `C-v'.  I couldn't see any difference compared to not
> having the option enabled.  All the text that's passing by is still
> fontified and scrolling doesn't seem faster.

The main point is, text continues to pass by.  What was happening was
that on an auto-repeated C-v, Emacs would hang (without scrolling), and
after releasing the key, it took quite a few seconds before the display
would be updated.  During this time Emacs was completely unresponsive.

With `use-default-face-for-fast-scrolling' at nil, all the text scrolled
over gets fontified, and lesser machines (such as mine) cannot keep up.
With the option set to t, only the text being displayed gets fontified.
The appearance may be of text continually scrolling, but this is an
illusion; only parts of the scrolled over text get fontified and

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.

> I've tried with C files and the persistency files of my working group's
> graph database (which would be my primer use-case for that feature).

As I say, maximise your frame first.

> Bye,
> Tassilo

Alan Mackenzie (Nuremberg, Germany).

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