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Re: Scrollbar thumbs

From: Jason Rumney
Subject: Re: Scrollbar thumbs
Date: Fri, 06 Nov 2009 07:55:51 +0800
User-agent: Thunderbird (Windows/20090812)

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.

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