Fallback accessibility themes

[Shaun McCance]

Currently, if an application needs to install some icons,
it installs them into the hicolor theme.  This allows the
icon to be themed, but ensures that the provided icon is
used as a fallback by all implementations.

In Gnome, we have three accessibility themes: HighContrast,
HighContrastInverse, and LowContrast.  It's not realistic
to expect these themes to provide icons for all the icons
that every single application installs.

Ideally, we'd like to tell developers to provide alternate
versions of their icons for accessibility purposes.  But
the only way they can do that is to install the icons into
the Gnome-specific accessibility icon themes.

I don't know if any other desktops provide similar themes
for accessibility, but it would be nice to have a set of
freedesktop-specified fallback icon themes that specific
accessibility themes can inherit from.  So, for example,
we would define the hicontrast theme.  Applications would
install high contrast versions of their icons into that
theme, and Gnome's HighContrast theme would inherit from
hicontrast.

Like hicolor, the accessibility fallback themes wouldn't
be "real" themes, in that there wouldn't be any actual
package that provides icons for them.  They would simply
be a place for application-specific icons that should be
used whenever an actual accessibility theme is used.

This would allow us to encourage developers to provide
icons for accessibility themes without asking them to
tie themselves to Gnome.

Thoughts?

--
Shaun