How to work with effects in GIMP Python?

[joeyeroq]

In GIMP 2 you could threshold the alpha channel (Layer > Transparency > Threshold Alpha...), in Python console equivalent was:

Code:

image = gimp.image_list()[0]
layer = image.layers[0]
# image,layer,threshold.
pdb.plug_in_threshold_alpha(image,layer,0)

In GIMP 3 Threshold Alpha has become a filter ("fx" icon next to the layer)
I can do in GIMP 3:

Code:

image = Gimp.get_images()[0]
layer = image.get_selected_layers()[0]
# Add Threshold Alpha layer fx (Layer > Transparency > Threshold Alpha...).
filter1 = Gimp.DrawableFilter.new(layer, 'gimp:threshold-alpha', 'My Threshold Alpha')
# Add Gaussian Blur layer fx (Filters > Blur > Gaussian Blur...).
filter2 = Gimp.DrawableFilter.new(layer, 'gegl:gaussian-blur', 'My Gaussian Blur')
layer.append_filter(filter1)
layer.append_filter(filter2)

But this does the filters in default settings.
How do I change the settings of the filters, for example how do i set the alpha value to 0 of 'My Threshold Alpha'?
   

[joeyeroq]

I couldn't find any usefull documentation on DrawableFilterConfig methods. I googled some more found this thread on gimpchat.com GIMP 3 now has GEGL automation in python console. So to set parameters for filters you do this:

Code:

# Get image and selected layer.
image = Gimp.get_images()[0]
layer = image.get_selected_layers()[0]
# Add Threshold Alpha layer fx (Layer > Transparency > Threshold Alpha...).
filter_threshold_alpha = Gimp.DrawableFilter.new(layer, 'gimp:threshold-alpha', 'My Threshold Alpha')

To print the parameters in the console you can use DrawableFilter.get_config().list_properties():  

Code:

for parameter in filter_threshold_alpha.get_config().list_properties():
    parameter.get_name(), parameter.get_default_value()
# To set the parameter to 0 you do
filter_threshold_alpha.get_config().set_property('value', 0.0)
# Append Threshold Alpha filter to the layer.
layer.append_filter(filter_threshold_alpha)

  Now let's add Gaussian Blur  

Code:

# Add Gaussian Blur layer fx (Filters > Blur > Gaussian Blur...).
filter_gaussian_blur = Gimp.DrawableFilter.new(layer, 'gegl:gaussian-blur', 'My Gaussian Blur')
# set properties for Gaussian Blur.
filter_gaussian_blur.get_config().set_property('std-dev-x', 5.5)
filter_gaussian_blur.get_config().set_property('std-dev-y', 5.5)
# If you set the properties after adding the filter to the layer you have to use:
filter_gaussian_blur.update()

  I tried to add all properties for Gaussian Blur at once but  

Code:

filter_gaussian_blur.get_config().set_properties(('std-dev-x', 1.5), ('std-dev-y', 1.5), ('filter', 'auto'), ('abyss-policy', 'clamp'), ('clip-extent', True))

 and  

Code:

filter_gaussian_blur.get_config().set_properties(5.5, 5.5, 'auto', 'clamp', True)

 didn't work either. To merge the filters down use:

Code:

layer.merge_filters()

     

How do you find out what the filter operation’s name are like 'gimp:threshold-alpha' and  'gegl:gaussian-blur' when using Gimp.DrawableFilter.new(drawable, operation_name, name)?

[Ofnuts]

Some pointers (no time to develop more that this ATM):

• https://gegl.org/operations/ (there may be some more that are gimp-specific).
  
• https://gitlab.gnome.org/GNOME/gimp/-/merge_requests/2008
  
• https://developer.gimp.org/api/3.0/libgimp/method.Drawable.merge_new_filter.html