Re: [Gimp-developer] How to deal with pixel-per-pixel operations?

[Øyvind Kolås <pippin gimp org>]

On Tue, Jun 11, 2013 at 1:32 AM, Alessandro Francesconi <
alessandrofrancesconi live it> wrote:

> Hello, I'm starting to write a GIMP plugin and I'm facing the problem of
> "pixel-per-pixel" algorithms and their speed.
> Without going on details, my algorithm should take every pixel in the
> image and for each one it must check its 24 neighbours, it does some simple
> calcs and finally it set a new color for the pixel.
>
> How to speed-up the execution? I tried with the easiest approach with a
> classic "for-in-for" loop but the computation is really slow. Looking
> around, I've seen some GIMP functions like:
>
> gimppixelfetcher — Functions for operating on pixel regions.
> gimppixelrgn — Functions for operating on pixel regions.
> gimpregioniterator — Functions to traverse a pixel regions.

All of the above functions are considered deprecated; even when developing
a GIMP plug-in and not a GEGL operation you would be encouraged to use
GeglBuffer APIs (search for "gegl" in gimp's plug-in directories.). Though
for a filter plug-in like you describe, the most proper way to do it now
and for the future is to write a GeglOperation that derives from the
provided GeglOperationAreaFilter like for instance:

https://git.gnome.org/browse/gegl/tree/operations/common/noise-spread.c

you'd probably want to fetch the entire neighborhood of the rectangular
region being processed though; rather than doing like that particular
plug-in which gegl_buffer_get's pixels one by one.

/pippin