Create a custom.xml for Gnome wallpaper slideshow

**** 29 November 2012 *****
Ran into a bug since I originally shared this:  If you use the link from the slideshow.xml for easy access by apps like gdm3setup make sure you either have it in a different folder than the images, or remove it before running the nautilus script. If you don't it will be added to the custom.xml and will not display that 'image' correctly.

My solution was to place them in /usr/share/GDM so I no longer have to worry about it.
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I use a nautilus script that I found via Webupd8 www.webupd8.org/2011/12/create… to create a wallpaper slideshow, but the problem is that to add one that's already been created is a PITA, at least to me.

That sent me on a quest to figure out how to add my custom wallpapers so they would show up in System Settings > Backgrounds so that I could create custom collections and easily select them.  I looked at numerous pages similar to this one askubuntu.com/questions/71008/… and this is what I ended up with.

My /usr/share/gnome-background-properties/custom.xml looks like this:

<?xml version="1.0" encoding="UTF-8"?>

<wallpapers>
<wallpaper deleted="false">

<name>Custom Backgrounds</name>

<filename>/usr/share/backgrounds/custom/custom.xml</filename>
<options>zoom</options>
   <pcolor>#ffffff</pcolor>
   <scolor>#000000</scolor>
</wallpaper>
</wallpapers>

So, after the nautilus script creates the slideshow.xml (whatever name you told it to use) you insert the path & filename info where indicated.  (Using a script is optional, you can use the the gnome-backgrounds.xml for a guide, or just add your images to it).

I use the system path because I use the same script as my GDM theme, which seems to require root access.

Now, when you open up System Settings > Backgrounds your new custom.xml file will show up as an image just like the other backgrounds that were installed with your system.

Note: This essentially just a knockoff of the adwaita.xml, the one that provides the time of day changes in the blue striped wallpaper

* Bonus, now, to use the same xml via an application like gdm3setup, which will only look for images, you create a link to the slideshow.xml (in my case /usr/share/backgrounds/custom/custom.xml) and give it a .jpg extension, mine is simply /usr/share/backgrounds/custom/custom.jpg).  Now you can navigate to that folder with gdm3setup and it will show up as a legitimate selection.  Of course you can mix & match, but if you like a smooth transition from the login screen to the desktop, you will have the dynamic wallpaper making a seamless transition.

I don't know if anyone even bothers to read these journal entries, but I can also explain how to add transparency to the login screen (get  rid of that solid gray look between the gdm wallpaper theme & the desktop wallpaper).

Anyway, if you have questions or problems feel free to ask, I'll do my best.  I know this works on Archlinux (and derivatives) and should work with any distro that has /usr/share/gnome-background-properties, which should include Ubuntu.