Rewrite the way scrolling for ScrollAreas is handled: Store
content position instead of scrollbar positions to keep position
on resize and promote moving the content instead of the contents
to as primary API.
Let the mousewheel scroll by fixed content offset instead of
scrollbar offset to make it actually usable (especially with
low scrolling distance).
Features:
- Various configurable styles.
- Working scroll bars, thanks to Tom
- Adequate REPL-ness.
See the wiki for more information!
http://wiki.flightgear.org/Interactive_Nasal_Console
N.B. This makes some (sane) changes to other Nasal files, including
expanding some of the Canvas API.
