GtkIconTheme provides a facility for looking up icons by name
and size. The main reason for using a name rather than simply
providing a filename is to allow different icons to be used
depending on what icon theme is selected
by the user. The operation of icon themes on Linux and Unix
follows the Icon
Theme Specification (http://www.freedesktop.org/Standards/icon-theme-spec). There is a default icon theme,
named hicolor where applications should install
their icons, but more additional application themes can be
installed as operating system vendors and users choose. Named icons are similar to the
facility, and the distinction between the two may be a bit confusing.
A few things to keep in mind:
- Stock images usually are used in conjunction with
., such as
GTK_STOCK_OK or
GTK_STOCK_OPEN. Named icons are easier to set up and therefore
are more useful for new icons that an application wants to
add, such as application icons or window icons.
- Stock images can only be loaded at the symbolic sizes defined
by the
GtkIconSize enumeration, or by custom sizes defined
by gtkIconSizeRegister, while named icons are more flexible
and any pixel size can be specified.
- Because stock images are closely tied to stock items, and thus
to actions in the user interface, stock images may come in
multiple variants for different widget states or writing
directions.
A good rule of thumb is that if there is a stock image for what
you want to use, use it, otherwise use a named icon. It turns
out that internally stock images are generally defined in
terms of one or more named icons. (An example of the
more than one case is icons that depend on writing direction;
GTK_STOCK_GO_FORWARD uses the two themed icons
"gtk-stock-go-forward-ltr" and "gtk-stock-go-forward-rtl".) In many cases, named themes are used indirectly, via GtkImage
or stock items, rather than directly, but looking up icons
directly is also simple. The GtkIconTheme object acts
as a database of all the icons in the current theme. You
can create new GtkIconTheme objects, but its much more
efficient to use the standard icon theme for the GdkScreen
so that the icon information is shared with other people
looking up icons. In the case where the default screen is
being used, looking up an icon can be as simple as:
icon_theme <- gtkIconThemeGetDefault()
result <- icon_theme$loadIcon("my-icon-name", 48, 0)
if (!result[[1]]) {
warning("Couldn't load icon: ", result$error$message)
} else {
pixbuf <- result[[1]]
## Use the pixbuf
}