My first instinct would be to say that ppm-load not setting it's output format is a bug, and that it should try to sniff the file in prepare() inorder to set the correct format. If you do format switching in gaussian-blur's process() then you'll also spoil the format detection of whatever is connected to gaussian's output.
As an alternative to that, I would be inclined to process ppm-load to a buffer then pass that buffer to a second graph. Finally (and please don't use this option), the reason you get that error is because the parent implementation of process() in gegl/operation/gegl-operation-filter.c calls gegl_operation_context_get_target for you, it is possible to override this and still use the rest of the filter class (see operations/common/over.c). On Wed, May 29, 2013 at 8:58 PM, Dov Grobgeld <dov.grobg...@gmail.com>wrote: > Hi all, > > Yesterday night I started playing around with converting the gaussian-blur > operation to only work on the channels that are part of the input pad. My > goal was to make the operation "format transparent", in the sense that the > output format should be equal to the input format. But after several > failures, I realized that I was stuck. > > The problem is as follows. I want to set my input format based on the > output format of the previous node. I'm building the following network: > > gegl:ppm-load → gegl:gaussian-blur → gegl:npy-save > > and I feed the ppm-load with a "Y u8" image. Now, the problem is that if I > in the gaussian-blur prepare function call: > > gegl_operation_get_source_format(operation, "input") > > it returns NULL. Why is that? Am I correct to assume that the prepare > calls are done before any processing has taken place? If so the ppm-load > still doesn't know what format it will set in its output pad. > > So instead I asked about the format in process(). But then I get the > following warning: > > (test-npy.py:2383): GEGL-gegl-operation-context.c-WARNING **: no format > for gegl:gaussian-blur 0x95bb9b0 presuming RGBA float > > I still haven't figured out exactly why this happens, but I would still > like to know if anyone knows what I'm doing wrong, and whether dynamically > choosing the input format based on the previous output format is even > possible? > > Thanks! > Dov > > > _______________________________________________ > gegl-developer-list mailing list > gegl-developer-list@gnome.org > https://mail.gnome.org/mailman/listinfo/gegl-developer-list > >
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