Xscreensaver will run several programs to continuously update the
screen instead of going blank.  You can specify the programs and their
arguments using resources.  You can also add dpms (power saver) options.

Xscreensaver will make use of any installed OpenGL libraries, such as
Mesa (also in the ports collection).

The client-server model employed by xscreensaver make it a superior choice
to xlock, since no separate auto-locking program is needed.  It's also
extremely easy to add new programs like xearth, or any other program that
can fill the root window as additional screensavers.

WWW: https://www.jwz.org/xscreensaver/