Comment 5 for bug 278941

My five cents: i discovered that the value of the "-pan" should always be smaller than or equal to "-duration". If "pan" is greater - images will not change during slideshow.

The easiest way to set the right values is:
- run xscreensaver-demo
- choose GLSlideshow plugin
- click Settings
- set "Crossfade duration" to the leftmost value (None) or to the very little fraction from the left
- click Ok.
Now, slideshow should work as expected.

Another way is to edit:
~/.xscreensaver
Find the string containing:
glslideshow -root
and add:
-pan 9 -duration 10
(or your comfortable values). Save file and run xscreensaver-demo

I think, the bug here is that the default values for this screensaver is invalid in xscreensaver-demo, and because of this - plugin won't run as expected. Steps to reproduce:
1. open ~/.xscreensaver with any editor
2. kill the string, containing "glslideshow -root"
3. save file
4. open xscreensaver-demo, select GLSlideshow plugin - default params will be loaded.
Result: preview pane shows only one constant image.
Expected: preview pane should display sequence of random images
5. click settings
6. set "Crossfade duration" to None
7. Click ok
Result: slide show runs as expected