Re: Scrollbar bug on OS X

[Stefan Monnier <monnier@iro.umontreal.ca>]

> I acknowledge your explanations on the other points - thanks. In the UI that
> I'd like to implement in order to conform to standards in my environment,
> the vertical slider size shows a proportion of _ displayed lines_ not
> document characters or real lines (those that end with a CR or LF). Whether

Since the height of lines can vary, the number of displayed lines can change
from one part of the buffer to another, so it's still not stable.
You really need to use the pixel size.

> visual change on the screen is more", and that b) both Windows and Mac
> software has sliders with a stable size.

The closest kind of software would be things like web-browsers for which
some details are relevant:
- the slider size changes as the page is being filled and rendered, so it's
  not nearly as stable as you make it out to be.
- html pages are typically small and web-browsers's algorithms are taylored
  for that case, they tend to become unusable when browsing large pages
  (like more than a megabyte), whereas it is considered important for Emacs
  to be able to comfortably edit multi-MB files (although there is also
  a limit).
- html-rendering becomes even more unusable if you start to actually
  interactively edit the 1MB page.
I.e. it's not just that Emacs hackers are incompetent, but it's that the
problem is difficult.

> Is there a way to store count-screen-lines statically and just update it
> when necessary?

Of course.  That's one of the tricks we'd have to use in order to get
"stable" slider sizes.  Problem is, I haven't yet heard of other useful
things we could do with that kind of extra info, so again: the amount of
work seems unjustified.


        Stefan