If this option is set, then the image-manipulating modes will select a random image file from disk, from the directory you specify in the text entry field. That directory will be recursively searched for files, and it is assumed that all the files under that directory are images.
If more than one of these options are selected, then one will be chosen at random. If none of them are selected, then an image of video colorbars will be used instead.
(All three of these options work by invoking the xscreensaver-getimage(1) program, which is what actually does the work.)
Some of the display modes display and manipulate text. The following options control how that text is generated. (These parameters control the behavior of the xscreensaver-text(1) program, which is what actually does the work.)
Host Name and Time
If this checkbox is selected, then the text used by the screen savers will be the local host name, date, time, and system load.
If this checkbox is selected, then the literal text typed in the field to its right will be used. If it contains % escape sequences, they will be expanded as per strftime(2).
If this checkbox is selected, then the contents of the corresponding file will be displayed.
If this checkbox is selected, then the given program will be run, and its output will be displayed.
If this checkbox is selected, then the given HTTP URL will be downloaded and displayed repeatedly. If the document contains HTML, RSS, or Atom, it will be converted to plain-text first.
Note: this re-downloads the document every time the screen saver runs out of text! It might be considered abusive for you to point this at a web server that you do not control, as it will probably be hitting that server multiple times a minute.
Power Management Enabled
Whether the monitor should be powered down after a period of inactivity.
If this option is grayed out, it means your X server does not support the XDPMS extension, and so control over the monitor's power state is not available.
If you're using a laptop, don't be surprised if this has no effect: many laptops have monitor power-saving behavior built in at a very low level that is invisible to Unix and X. On such systems, you can typically only adjust the power-saving delays by changing settings in the BIOS in some hardware-specific way.
If Power Management Enabled is selected, the monitor will go black after this much idle time. (Graphics demos will stop running, also.)
If Power Management Enabled is selected, the monitor will go into power-saving mode after this much idle time. This duration should be greater than or equal to Standby.
If Power Management Enabled is selected, the monitor will fully power down after this much idle time. This duration should be greater than or equal to Suspend.
Fade To Black When Blanking
If selected, then when the screensaver activates, the current contents of the screen will fade to black instead of simply winking out. (Note: this doesn't work with all X servers.) A fade will also be done when switching graphics hacks (when the Cycle After expires.)
Unfade From Black When Unblanking
The complement to Fade Colormap: if selected, then when the screensaver deactivates, the original contents of the screen will fade in from black instead of appearing immediately. This is only done if Fade Colormap is also selected.
When fading or unfading are selected, this controls how long the fade will take.
On 8-bit screens, whether to install a private colormap while the screensaver is active, so that the graphics hacks can get as many colors as possible. This does nothing if you are running in bit or better.