How to mask a layer from a channel in GIMP with Python?

Question

I've been 3 days searching for documentation about python-fu for GIMP 2.8, and the one I find is great, but deprecated.

So I'm now stuck at this place: I've created 3 color channels, and want to add each one of them as a mask to each of 3 layers.

What I've done till now: (manually load the image, and create 3 color channels for lights, middle tones and shadows);

Get it's ID, with:

ima = gimp.image_list()[0]

Get the layer ID and duplicate the layer 3 times:

layn = pdb.gimp_layer_new_from_visible(ima, ima, 'dup')
pdb.gimp_image_insert_layer(ima, layn, None, -1) 

Now I have an image with three layers and want to add a layer mask to each of the 3 layers but from the 3 different color channels... but I don't know how.

Answer 1

The API doesn't seem to support creating a mask directly from a random channel. But you can create a mask from the selection, so:

1. Copy your channel into the selection

   pdb.gimp_image_select_item(image,CHANNEL_OP_REPLACE,channel)
   

2. Create the mask

   mask=layer.create_mask(ADD_SELECTION_MASK)
   

3. Add the mask to the layer:

   layer.add_mask(mask)