So it seems that now it keeps a history of wallpapers. Is that history's length limited, and if so, how (a certain amount of memory, a maximum number of images paths and names, some other method)?
I suppose a bit of explanation is in order:
1) When you click the "Start wallpaper switching" button, Spews creates a list of images based on what you can configured and checked in the "Image folders" section. The list then has any dupes removed and is randomised. This method removes any chance that a wallpaper will be seen twice during a list's run.
3) Spews then uses this list, starting at the top and moving in order but remember the list is randomised every time you start the switching so the order is not the filepath image order.
4) Selecting the previous wallpaper goes back one image, at a time, in the list. However, selecting next wallpaper ALWAYS goes to the next random wallpaper in the list.
For example, let's assume you have your list of wallpapers that Spews has randomised and is now switching through. Image #3 is displayed on your desktop. Selecting previous wallpaper
would display iamge #2. Selecting previous wallpaper
again would display image #1. Selecting next wallpaper
(or having the next image display on your configured time interval) would display image #4. At this point, selecting previous wallpaper
would display #3, #2, and so on. Maybe slightly illogical, yes, but I would have had to create a second "next wallpaper" function which seems a bit inelegant to me.
So, to answer your question, Spews doesn't use any more memory for this functionality (because it's using the same list). Clear as mud, eh?