How do I save (export) all layers with gimp's script fu?

Question

With gimp fu, I can save the content of one layer (at least, that is how I interprete the definition of gimp_file_save because it takes the parameter drawable).

Now, I have the following script:

from gimpfu import *

def write_text():

    width  = 400
    height = 100

    img = gimp.Image(width, height, RGB)
    img.disable_undo()


    gimp.set_foreground( (255, 100, 20) )
    gimp.set_background( (  0,  15, 40) )

    background_layer = gimp.Layer(
                           img,
                           'Background',
                           width,
                           height,
                           RGB_IMAGE,
                           100,
                           NORMAL_MODE)

    img.add_layer(background_layer, 0)
    background_layer.fill(BACKGROUND_FILL)

    text_layer = pdb.gimp_text_fontname(
                    img,
                    None,
                    60,
                    40,
                    'Here is some text',
                    0,
                    True,
                    30,
                    PIXELS,
                    'Courier New'
                )

    drawable = pdb.gimp_image_active_drawable(img)

#   Either export text layer ...
#   pdb.gimp_file_save(img, drawable, '/temp/tq84_write_text.png', '?')

#   .... or background layer:
    pdb.gimp_file_save(img, background_layer, '/temp/tq84_write_text.png', '?')

register(
  proc_name     = 'tq84_write_text',
  blurb         = 'tq84_write_text',
  help          = 'Create some text',
  author        = 'Rene Nyffenegger',
  copyright     = 'Rene Nyffenegger',
  date          = '2014',
  label         = '<Toolbox>/Xtns/Languages/Python-Fu/_TQ84/_Text',
  imagetypes    = '',
  params        = [],
  results       = [],
  function      = write_text
)

main()

When I use pdb.gimp_file_save(img, drawable, '/temp/tq84_write_text.png', '?') to save the image, It will only export the "text" layer. Yet, If I use pdb.gimp_file_save(img, background_layer, '/temp/tq84_write_text.png', '?') it will only export the background. So, how can I export both layers into one image (as the menu File -> Export As would do).

Answer 1

What is done internally, even by GIMP file-exporter plug-ins for all formats is: duplicate the image, merge all visible layers, them save the resulting drawable.

This is easier, and take less resources than it sounds. Effectively you just have to replace your save line

pdb.gimp_file_save(img, background_layer, '/temp/tq84_write_text.png', '?')

by

new_image = pdb.gimp_image_duplicate(img)
layer = pdb.gimp_image_merge_visible_layers(new_image, CLIP_TO_IMAGE)
pdb.gimp_file_save(new_img, layer, '/temp/tq84_write_text.png', '?')
pdb.gimp_image_delete(new_image)

(The last call just "deletes" the new image from program memory, freeing up the resources, of course)