-The \fIrotzoomer\fP program grabs an image of the screen, then picks
-rectangles and draws scaled and rotated animations of that part of
-the screen.
+The \fIrotzoomer\fP program grabs an image, then picks
+rectangles and draws scaled and rotated animations of that
+section.
+
+The image that it manipulates will be grabbed from the portion of
+the screen underlying the window, or from the system's video input,
+or from a random file on disk, as indicated by
+the \fIgrabDesktopImages\fP, \fIgrabVideoFrames\fP,
+and \fIchooseRandomImages\fP options in the \fI~/.xscreensaver\fP
+file; see
+.BR xscreensaver-demo (1)
+for more details.