Re: gtk scroll bar deficiency

[Jason Rumney]

David Reitter wrote:
> For the scroll-bar, a reasonable estimate would do the job (count line
> lengths in various randomly sampled portions of the buffer if the
> buffer is big): the scroll-bar is a visual tool and not an exact science.

An reasonable estimate is what we have now. If the estimate is wrong,
then the results are one of:
  * User can't scroll to the bottom of the buffer - looks like a bug.
  * Scrolling jumps near the bottom of the buffer because we tried to
fix the above bug.
  * Scrollbar thumb size changes as you scroll, because we tried to fix
the first bug a different way.
  * Scrolling overshoots because we let the bottom of the buffer scroll
to the top of the screen to avoid the above bugs (current behaviour).


The only way to improve on that reasonable estimate is to do an exact
calculation - which requires pre-rendering the entire buffer to figure
out where lines need to wrap, and how tall each line needs to be.