Re: Scrollbar thumbs

[Jason Rumney <jasonr@gnu.org>]

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.