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Re: Scrollbar thumbs

From: David Kastrup
Subject: Re: Scrollbar thumbs
Date: Fri, 06 Nov 2009 09:42:53 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.1.50 (gnu/linux)

Jason Rumney <address@hidden> writes:

> David Kastrup wrote:
>> The "design flaw" is that Emacs has a variable line height.  An editor
>> is primarily supposed to deal with lines of text, not with continuous
>> graphical panes.  And previous to Emacs 21, Emacs only dealt with lines
>> of text of constant height.  Previous to Emacs 19, the lines
>> corresponded 1:1 to the screen lines.
> Even Emacs 19 had line wrapping, so counting CR characters as the file
> is read (as some simple text editors do) has never been the solution
> to this problem.  The only solution seems to be to render the entire
> buffer offscreen in background, adjusting the scrollbar as we get more
> detailed information about the real contents of the buffer.  This is
> what word processors, web browsers and other complex applications do -
> you see the first page quite quickly, then you see the scroll bar
> growing as it renders the buffer in background.  Most applications do
> not even make an initial guess, so you cannot scroll to the bottom of
> the buffer until the background rendering is finished. The application
> then needs to use extra memory to cache the metrics it has calculated
> to avoid having to rerender the entire document on every change.

Actually, the inability to get such an application in combination with
the castrated scroll bar semantics scroll half a screen down is quite
annoying.  The only way you can scroll a half-screen (without
Athena-style scrollbar behavior) is by dragging, and particularly
dragging in large documents while the scrollbar self-updates is utterly
haphazard.  Usually you completely use your place.

I don't see that this is a useful model of behavior for an editor.

David Kastrup

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