Former gimp_color_scale_entry_new() is finally replaced by the
GimpColorScaleEntry implementation.
Both places which used it (GimpColorScales and compose plug-in) now use
the new widget.
Also making "upper" and "lower" properties of GimpScaleEntry into
construction properties, and create the main GtkAjustment at init, so
that we are sure that lower and upper bounds are properly set before we
set the value (when setting all properties at once, we cannot ensure
that these limit properties are set before the "value" one).
I updated GimpScaleEntry and GimpColorScaleEntry header to use
respectively the macros G_DECLARE_DERIVABLE_TYPE and
G_DECLARE_FINAL_TYPE.
Though having the `priv` structure directly in the object data is
extremely comfortable for developing (hence we don't want to use this
macro on core code as it makes coding a bit more bothersome), it is true
that it does not make for a very pretty public interface (showing a
`priv` member which nobody can actually use, and a private type which
has no associated functions). So it might be a good idea to use these
macros at least on libgimp side.
I am still not sure though if it is a good idea so we could say it's an
experiment. At least the docs says that using G_DECLARE_FINAL_TYPE does
not affect ABI stability as it can later be changed into a
G_DECLARE_DERIVABLE_TYPE because the class structure stays private. So
at least that's one good point.
P.S.: also reordering gimpwidgets.def.
Similarly to GimpScaleEntry, this is meant to replace usage of
gimp_color_scale_entry_new() by having a proper widget. This is a child
class of GimpScaleEntry which simply replaces the GtkScale by a
GimpColorScale by adding a GimpScaleEntry class method to create the
scale widget (only restriction: it must be a GtkRange subtype).
This also triggers me to rename gimp_scale_entry_get_scale() into
gimp_scale_entry_get_range() (as well as the 2 plug-ins already using
this function).
Jehan