In GimpHistogram, get rid of the "n-channels" property and
corresponding gimp_histogram_n_channels() function. The former
returned the actual number of channels, but this wasn't too useful,
as channel values may not be sequential; the latter returned the
number of components. Instead, add an "n-components" property and
a corresponding gimp_histogram_n_components() function, both of
which return the number of components. Furthermore, add a
gimp_histogram_has_channel() function, which determines if the
histogram has a given channel; this allows for simple testing for
channel availability, which was done wrong in various places.
Adjust the GimpHistogram code for the changes, and clean it up,
fixing a few bugs.
Adjust users of GimpHisotgram for the changes. In particular,
in GimpHisotgramView, fix the channel-availability test when
setting the view's histogram (which happens whenever the active
drawable's preview is frozen), to avoid erroneously swithcing the
view's channel back to "Value" when a non-RGB channel is selected.
(cherry picked from commit fc17f0ed0c)
More than 2000 lines of code less in app/, instead of
if (instance->member)
{
g_object_unref/g_free/g_whatever (instance->member);
instance->member = NULL;
}
we now simply use
g_clear_object/pointer (&instance->member);
