iPhone 4 layer export script for Gimp

I often mockup iPhone interfaces on the Gimp, then exporting each layer for use as backgrounds. For iOS 4 each image needs to be exported twice: one at full resolution with @2x in its filename, and once at half-resolution without the @2x. e.g. nav_bg@2x.png and nav_bg.png.

Exporting layers by hand gets old real quick. Thankfully the Gimp supports scripting in my favourite language: python. Even better, Chris Mohler had already written a script to do something very similar, so all I needed to do was make some simple adjustments:
#!/usr/bin/env python
# -*- coding: <utf-8> -*-
# Author: Chris Mohler <cr33dog@gmail.com>
# Copyright 2009 Chris Mohler
# "Only Visible" and filename formatting introduced by mh
# License: GPL v3+
# Version 0.4
# GIMP plugin to export layers as PNGs
# modified by Shuning Bian 2011

from gimpfu import *
import os, re

gettext.install("gimp20-python", gimp.locale_directory, unicode=True)

def format_filename(layer):
    layername = layer.name.decode('utf-8')
    filename1 = layername + "@2x.png"
    filename2 = layername + ".png"
    return filename1,filename2

def get_layers_to_export(img):
    layers = []
    for layer in img.layers:
        if layer.visible:
    return layers

def export_layers(img, path):
    dupe = img.duplicate()
    savelayers = get_layers_to_export(dupe)
    for layer in dupe.layers:
        layer.visible = 0 
    for layer in dupe.layers:
        if layer in savelayers:
            layer.visible = 1

            if layer.mask:
                pdb.gimp_layer_remove_mask(layer, 0)

            filename1,filename2 = format_filename(layer)
            fullpath = os.path.join(path, filename1);
            tmp = dupe.duplicate()
            pdb.file_png_save(tmp, tmp.layers[0], fullpath, filename1, 0, 9, 1, 1, 1, 1, 1)

            imgwidth = pdb.gimp_image_width(img)
            imgheight = pdb.gimp_image_height(img)
            pdb.gimp_image_scale_full(tmp, imgwidth/2, imgheight/2, 2)

            fullpath = os.path.join(path, filename2)
            pdb.file_png_save(tmp, tmp.layers[0], fullpath, filename2, 0, 9, 1, 1, 1, 1, 1)


    blurb=("Export visible layers as PNG"),
    help=("Export all visible layers as individual PNG files."),
    author=("Chris Mohler <cr33dog@gmail.com> + sbian"),
    copyright=("Chris Mohler"),
    label=("as _PNG"),
        (PF_IMAGE, "img", "Image", None),
        (PF_DIRNAME, "path", "Save PNGs here", os.getcwd()),
    menu=("<Image>/File/E_xport Layers"), 
    domain=("gimp20-python", gimp.locale_directory)