How to make a mask from a selection?

[gasMask]

Hi,

I'm not sure that I understand the problem, but I wrote some code for exporting a selection for a mask. The original image is modified but is then restored back to its original state. I haven't tested the code, so there could be bug(s).

Code:

#!/usr/bin/env python3
import gi
gi.require_version('Gimp', '3.0')
from gi.repository import Gegl, Gimp          # noqa


def export_selection_as_white_layer(image):
   """
   Given an image, export the current selection as a new image
   from the current selection filled with white and having a black background.

   Steps:
   1. Create a new image to hold a mask-like layer.

   2. Create a white selection layer.

   3. Transfer the white selection layer to the new image.

   4. Export the new image as a PNG file with its alpha layer turned off.

   5. Restore the original image back to its original state.

   image: Gimp.Image
       Has a selection that is to be exported a mask-like layer.
   """
   # Create a temporary image.
   w, h = image.get_width(), image.get_height()
   temp_image = Gimp.Image.new(w, h, Gimp.ImageBaseType.RGB)
   display = Gimp.Display.new(temp_image)

   # Create a new layer for a white selection on top of the original image.
   white_selection_layer = Gimp.Layer.new(
       image,
       "White Selection Layer",
       w,
       h,
       Gimp.ImageType.RGBA_IMAGE,
       100.,
       Gimp.LayerMode.NORMAL
   )

   image.insert_layer(white_selection_layer, None, 0)

   # Fill the selection with white.
   Gimp.context_set_opacity(100.)
   Gimp.context_set_paint_mode(Gimp.LayerMode.NORMAL)
   Gimp.context_set_foreground(Gegl.Color.new('white'))
   white_selection_layer.edit_fill(Gimp.FillType.FOREGROUND)

   # Create a new layer from the white selection layer.
   layer_copy = Gimp.Layer.new_from_drawable(
       white_selection_layer, temp_image
   )

   temp_image.insert_layer(layer_copy, None, 0)

   # Export the temp-image as a PNG file and without an alpha
   # so that the background is black.
   # * Insert export PNG code here. *

   # Remove the temporary layer from the original image.
   image.remove_layer(white_selection_layer)

   # Delete the new image.
   # display.delete()

I've left the export PNG code out as you've stated you already have that figured-out.

Charles