man xeyes (1): a follow the mouse X demo

SYNOPSIS

xeyes [-option ...]

Xeyes watches what you do and reports to the Boss.

-fg foreground color: choose a different color for the pupil of the eyes.
-bg background color: choose a different color for the background.
-outline outline color: choose a different color for the outline of the eyes.
-center center color: choose a different color for the center of the eyes.
-backing { WhenMapped Always NotUseful }: selects an appropriate level of backing store.
-geometry geometry: define the initial window geometry; see X(7).
-display display: specify the display to use; see X(7).
-bd border color: choose a different color for the window border.
-bw border width: choose a different width for the window border.
-shape: uses the SHAPE extension to shape the window. This is the default.
+shape: disables use of the SHAPE extension to shape the window.
-render: uses Xrender to draw anti-aliased eyes. This is the default if xeyes has been compiled with Xrender support.
+render: disables Xrender and draws traditional eyes.
-distance: uses an alternative mapping, as if the eyes were set back from the screen, thus following the mouse more precisely.

Keith Packard, MIT X Consortium
Copied from the NeWS version written (apparently) by Jeremy Huxtable as seen at SIGGRAPH '88