The version of Gnome in Ubuntu 10.04 has the ability to automatically change through a defined set of files. Unfortunately, there’s no simple way to do this via the gui (I originally assumed that you just assigned a folder to be your background) so I whipped up a quick Python script. This could probably have been done in bash, but I took the lazy way out. I’m also sure I could have used some existing XML library, but the file is fairly simple, so I just used file.write(). If any glaring errors are pointed out, or if I feel like implementing XML properly, I’m sure I’ll post a revised version sometime soon, but for now, here’s the program:

Here’s a link to the source, in case WordPress fubars Python’s indentation.

#!/usr/bin/python

import os, os.path, sys, optparse

IMG_FILETYPES = ['.jpg', '.jpeg', '.png', '.gif', '.bmp', '.svg']

def gen_bg_xml(directory, duration=1795.0, transition=5.0):
    if not os.path.isdir(directory):
        print “Error: {0} is not a valid directory”.format(directory)
        sys.exit(2)

    xmlfile = os.path.join(directory, “background.xml”)
    xml = open(xmlfile, mode=’w')

    xml.write(“<background>\n”)
    xml.write(“  <starttime>\n”)
    xml.write(“    <year>2010</year>\n”)
    xml.write(“    <month>01</month>\n”)
    xml.write(“    <day>01</day>\n”)
    xml.write(“    <hour>00</hour>\n”)
    xml.write(“    <minute>00</minute>\n”)
    xml.write(“    <second>00</second>\n”)
    xml.write(“  </starttime>\n”)

    files = os.listdir(directory)
    l = files[:] # Copy the list so we have something to iterate through
    for f in l:
        name, ext = os.path.splitext(f)
        if not ext in IMG_FILETYPES:
            files.remove(f)
            continue

    for f in files:
        absf = os.path.join(directory, f)
        if not files.index(f) == 0:
            xml.write(“    <to>{0}</to>\n”.format(absf))
            xml.write(“  </transition>\n”)
        xml.write(“  <static>\n”)
        xml.write(“    <duration>{0}</duration>\n”.format(duration))
        xml.write(“    <file>{0}</file>\n”.format(absf))
        xml.write(“  </static>\n”)
        xml.write(“  <transition>\n”)
        xml.write(“    <duration>{0}</duration>\n”.format(transition))
        xml.write(“    <from>{0}</from>\n”.format(absf))
        if files.index(f) == len(files) – 1:
            xml.write(“    <to>{0}</to>\n”.format(
                      os.path.join(directory, files[0])))
            xml.write(“  </transition>\n”)
    xml.write(“</background>”)
    xml.flush()
    xml.close()

if __name__==”__main__”:
    p = optparse.OptionParser(usage=”usage: %prog [options] directory”)
    p.add_option(‘–duration’, ‘-d’, default=”1795.0″)
    p.add_option(‘–transition’, ‘-t’, default=”5.0″)
    options, arguments = p.parse_args()
    if not len(arguments) == 1:
        p.error(“incorrect number of arguments”)
    sys.exit(1)
    gen_bg_xml(arguments[0], options.duration, options.transition)

Whew, escaping all those tabs was annoying.