It is this way possible to set a drawable as auxiliary input to a filter
in C and GObject-Introspected bindings.
Note that such filters can only be merged, not appended
non-destructively for the time being.
When calling gimp_drawable_filter_get_config() the first time, we don't
want the config's properties to be at default values, but instead to be
set same as they are on core app.
On further calls though, we don't touch the values, because they may be
out-of-sync until the next call to gimp_drawable_filter_update().
Similarly to the config arguments, the set functions are not directly
calling core. Instead they are queuing changes until
gimp_drawable_filter_update() is run.
It is now possible to sync the GimpDrawableFilterConfig with core.
Another (simpler on usage) possibility could have been to sync
automatically when a property is updated. But considering that some
filters can be quite slow to render (especially in real-life usage when
working on possibly very big files), and especially that on bindings
with no variable args, scripts will likely have to edit properties one
by one, it could make editing multiple properties very slow. Therefore
the chosen solution is that editing properties stay local on libgimp and
all changed properties are synced with core at once (with a frozen
render until the end for single computation) when calling
gimp_drawable_filter_update().
This is mostly an empty shell whose goal is to serve as base class for
specific dynamically generated per-operation subclasses, which will have
properties mimicking the arguments of the GEGL operation.
Most of the fundamental type args will just use the base GLib param spec
types instead of GEGL ones.
As a special case, the GeglParamEnum arguments are transformed into
GimpChoice param specs on libgimp side. The reason is that most of the
time, enum types are created within the scope of an operation code only
and cannot be properly reconstructed over the wire. I could just
transform these into an int type (which is mostly what is done in GEGL
right now when running an op with such arg), but GimpChoice allow much
nicer string-type args, which make much more semantic code. This class
was initially created for plug-ins, but it would work very well to run
GEGL ops on drawables. So let's do it.
Finally add a gimp_drawable_filter_get_config() to request the current
config of a filter.
Note that right now, we can't do much with this config object other than
observing an operation args and default values. Being able to update a
filter's settings will come up in further commits.
A few functions were added, but the main one is
gimp_drawable_get_filters() to request the list of filters applied
non-destructively on a drawable. We can't do much with these for the
time being, but this will come.
WIP.
Jehan