auto-refresh for icon preview

[Jon A. Cruz]

Icon preview would be much more usable if there was an option to update the
previews in real time.

[Jon A. Cruz (jon-joncruz)]

Committed as of revision 9390.

[su_v (suv-lp)]

The new 'Auto-refresh' feature from r9390 for the Icon Preview slows down working in larger icon-set files, for example when editing Inkscape's own 'icons.svg', especially if an alternative icon-set is displayed in a second window.

Proposing to revert the change or make 'Auto-refresh' an option to be turned on/off:
- Increasing the timer for the auto-refresh in the sources (changing the value for 'timer->elapsed()' from 0.1 to 1.0 in 'src/ui/dialog/icon-preview.cpp') doesn't really solve the issue (tested with current Inkscape 0.47+devel on OS X 10.5.8, using a MBP with 2.4 GHz Intel Core 2 Duo, 2GB RAM).
- When running idle in the background while the Icon Preview is open, Inkscape continuously uses 90-100% CPU of one of the two cores.
- Closing the Icon Preview dialog when using the option to preview '[x] Selection' without deselecting the current object doesn't stop the auto-refreshing process i.e. Inkscape keeps using a lot of CPU resources.

[su_v (suv-lp)]

Another comment after testing the current Icon Preview dialog (still with 'timer->elapsed()' changed from 0.1 to 1.0, Inkscape 0.47+devel r9471 on OS X 10.5.8, same hardware) with Gnome icon files mentioned in bug #270983 by Jimmac:

- The performance issue appears worse with more complex icons, even if the file contains far fewer of them compared to Inkscape's big icon file. Editing a detail of one of the gnome icons while Icon Preview is open is close to impossible.
- Conceptually there is a very important feature missing to make Icon Preview useful with auto-refresh: the user needs to be able to lock the preview to a selection, else the preview always changes to the current object which might be a small path or shape within the icon. Currently the preview works like a continuously zooming looking glass, its strength however IMHO would be to (optionally) auto-refresh a preview of a specific (or locked) selection of the drawing (aka the icon) at several sizes while letting the user work on some details of the icon in the main window.