[gdal-dev] Callbacks for next-gen Python bindings

[Ari Jolma]

Howard Butler kirjoitti:
> All,
>
> I have just committed rudimentary typemaps and support code for Python 
> function callbacks and the generic GDAL TermProgress methods in the 
> next-gen interface files.  This was one of the last major pieces of 
> missing functionality that existed in the old-gen bindings that was 
> preventing us from porting over a number of scripts in ./pymod.
>
> Additionally, I have created a new interface file, Operations.i, and 
> placed GDAL raster operations like ComputeMedianCutPCT, DitherRGB2PCT, 
> and ReprojectImage in this file to de-bulk gdal.i, which was getting a 
> little bit bloated after adding in the new methods.
>
> I would like to request making a change to Driver.CreateCopy.  It is 
> currently missing arguments for callback and callback_data, which 
> existed in the old-gen bindings.  I propose adding them and having 
> them default to NULL as is currently done.  Does anyone foresee an 
> issue with doing so?

I added a support and test for this type of callback into the Perl 
bindings. The callback is a Perl subroutine.

In writing the callbacks the problem was that Swig does not seem to 
support input typemaps with more than one effective parameters. I would 
need to manage the interplay because the pointer to the Perl subroutine 
is carried by the callback data. I could not find a way to write the 
typemap without hard coding the serial number of one of the parameters 
(callback_data). This is partially due to them being optional. If they 
were not, I could trust that the callback_data typemap really sets the 
callback_data parameter.

So, I would favor having them required and add an extra (Perl) layer... 
Hm, In fact I think I can add an extra layer anyway, which adds them and 
then I could trust that the callback_data is really set as it should be.

Howard, now that I'm talking to you, I think the "%typemap(out) char 
**options" has a bug in the Python bindings as it had one in the Perl 
one. It discards the last option.

Ari

>
> Howard
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-- 
Prof. Ari Jolma
Geoinformaatio- ja paikannustekniikka / Geoinformation and positioning
Teknillinen Korkeakoulu / Helsinki University of Technology
tel: +358 9 451 3886 address: POBox 1200, 02015 TKK, Finland
Email: ari.jolma at tkk.fi URL: http://www.tkk.fi/~jolma