Re: [Gimp-developer] How to call gimp_export_image() from Pythonplugin

[Vladimir Rutsky <rutsky vladimir gmail com>]

On 20.06.2014 04:42, Joao S. O. Bueno wrote:
> On 19 June 2014 20:38, Ed . <ej_zg hotmail com> wrote:
> > My understanding is that libgimp is for C plugins. Many libgimp functions
> > are in fact calls to PDB functions - see libgimp/gimppainttools_pdb.c for
> > example. The distinction between "high" and "low" level is not the one used
> > to determine what is in the PDB and what is not - despite what you say,
> > there are gimp-drawable-set-pixel and gimp-drawable-get-pixel procs in the
> > PDB.
> >
> > It seems you are knowledgeable in writing interface code for Python. Why not
> > add gimp_export_image to the available python functions?
> Because it is not there.
>
> One problem with the current implementation of Pygimp is exactly that it uses
> C to wrap around calls do libgimp.
> The problem with this approach is that one loses all the dynamic aspects from
> Python for these objects:
> The GIMP Python objects,as exposed in pygimp are "native" objects - as such
> they can not be modified by pure Python code.
>
> For writing Python plug-ins one does either use the objects ofered in Pygimp,
> with the functions enabled there in C code that requires a ton of
> boiler-plate for eachmethod made available,
> or use the Python PDB module, which allows one to call GIMP via the PDB.
>
>
> So, if it is not clear yet, the "gimp_file_export" function just is
> _not_ there.
> It can be made available by a C patch in pygimp - but that is adding
> functionality to a stable series.
> Or it could be made available through the PDB - which would also make
> it work from script-fu,
> and whatever other bindings happen to work. That is also adding new
> functionality.
>
> The correct thing to do is to add it both ways - as an "export" method
> for image objects,
> and as a PDB call - in the 2.9 branch.
>
> Now, talking about new features, you where the one experiencing with
> GIMP and GIO - that, on the contrary of this simple call, is something
> that matters: I'd very much like to rewrite GIMP Python using
> GIO - (so this kind of stuff would be a non issue in the future:
> everything available in C is ready without
> needing explicit wrappers with boiler plate code) - how far did you
> get with the GIO stuff?

What is GIO?
I heard about https://developer.gnome.org/gio/, but from it's 
description I don't get how it can be related to GIMP and it's plugins?


--
Vladimir Rutsky


> > -----Original Message----- From: Vladimir Rutsky
> > Sent: Thursday, June 19, 2014 11:52 PM
> > To: Ed .
> > Cc: gimp-developer
> >
> > Subject: Re: [Gimp-developer] How to call gimp_export_image() from
> > Pythonplugin
> >
> > On 19.06.2014 22:09, Ed . wrote:
> > > It is not a PDB function, but a libgimp (C) function. Since pygimp can do
> > > gimpui stuff (also C functions), there is no conceptual reason why pygimp
> > > shouldn't also handle gimpexport (which is where gimp_export_image lives).
> >
> > Which functions in GIMP goes to PDB, and which stays only in libgimp?
> >
> > As I understand, libgimp should contain _all_ functionality, that may be
> > needed for external C plugins. So it's "low-level" library.
> >
> > PDB functions are designed to be called from scripts for automation and
> > easer writing custom plugins in Scheme/Python/Perl scripts.
> > So there mostly should be "high-level" functions, since there is no
> > point in calling "low-level" operations, like set_pixel(), due to
> > performance overhead of PDB.
> >
> > gimp_export_image() is "high-level" function: it does several operations
> > on image as whole and optionally asks user for some input.
> > If gimp_export_image() would be available though PDB, it could be called
> > from any "fu"-script, that can call PDB functions, and there would be no
> > need to export it specifically in Python, Perl, Ruby, C#...
> >
> > Correct me if I'm wrong, since I'm new to PDB and GIMP development.
> >
> > > I thought that in Python it was straightforward to access C functions?
> > > This is simply a function that returns an integer, albeit one that uses the
> > > GIMP UI - which pygimp already can initialise.
> >
> > Best way to use C functions from Python is to write wrapper module in C
> > that will export methods as Python functions/classes (just as
> > GIMP-Python does).
> > Also you can load shared object and call C-function directly using
> > libffi library (presented as ctypes module in Python), but this
> > error-prone and really hackish way.
> >
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