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

[Vladimir Rutsky <rutsky vladimir gmail com>]

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.

> -----Original Message----- From: Vladimir Rutsky
> Sent: Thursday, June 19, 2014 6:24 PM
> To: João Sebastião de Oliveira Bueno
> Cc: Ed . ; gimp-developer
> Subject: Re: [Gimp-developer] How to call gimp_export_image() from 
> Pythonplugin
>
> On Wed, Jun 18, 2014 at 9:52 PM, Joao S. O. Bueno <gwidion gmail com> 
> wrote:
> > IS it available throught the PDB?
> > Most GIMP - Python functions are done via PDB, except pixel-region
> > manipulation stuff.
> > If it is not in the PDB, it is not availabl in GIMP 2.8 - the current
> > GIMP Python structure has to
> > special cases a lot of things to work aside from the PDB, and doing so
> > is not minor stuff
> > done inside a release cycle.
> >
> > Making the 3-4 above calls are straightforward - I see no reason to
> > violate the principle of no new features inside a release to add this.
> > In GIMP 2.10, the export feature will also have to deal with precision
> > management, and besides this export function, a class of PDB calls
> > dealing with precision needs
> > to be added as well.
>
> Joao, Ed,
>
> so gimp_export_image() should be exported to Python though PDB (to all
> plugins) or by writing custom export code as done for some functions
> to export it only to Python?
>
> --
> Vladimir Rutsky