epicycle(6) XScreenSaver manual epicycle(6)

NAME

epicycle - draws a point moving around a circle which moves around a
cicle which...

SYNOPSIS

epicycle [--display host:display.screen] [--root] [--window-id
number][--window] [--mono] [--install] [--noinstall] [--visual viz]
[--colors N] [--foreground name] [--color-shift N] [--delay
microseconds] [--holdtime seconds] [--linewidth N] [--min_circles N]
[--max_circles N] [--min_speed number] [--max_speed number]
[--harmonics N] [--timestep number] [--divisor_poisson probability]
[--size_factor_min number] [--size_factor_max number] [--fps]

DESCRIPTION

The epicycle program draws the path traced out by a point on the edge
of a circle. That circle rotates around a point on the rim of
another circle, and so on, several times. The random curves produced
can be simple or complex, convex or concave, but they are always
closed curves (they never go in indefinitely).

You can configure both the way the curves are drawn and the way in
which the random sequence of circles is generated, either with
command-line options or X resources.

OPTIONS

--display host:display.screen
Specifies which X display we should use (see the section
DISPLAY NAMES in X(1) for more information about this
option).

--root Draw on the root window.

--window-id number
Draw on the specified window.

--window
Draw on a newly-created window. This is the default.

--mono If on a color display, pretend we're on a monochrome display.
If we're on a mono display, we have no choice.

--install
Install a private colormap for the window.

--noinstall
Don't install a private colormap for the window.

--visual viz
Specify which visual to use. Legal values are the name of a
visual class, or the id number (decimal or hex) of a specific
visual. Possible choices include

default, best, mono, monochrome, gray, grey, color,
staticgray, staticcolor, truecolor, grayscale, greyscale,
pseudocolor, directcolor, number

If a decimal or hexadecimal number is used,
XGetVisualInfo(3X) is consulted to obtain the required
visual.

--colors N
How many colors should be used (if possible). The colors are
chosen randomly.

--foreground name
With --mono, this option selects the foreground colour.

--delay microseconds
Specifies the delay between drawing successive line segments
of the path. If you do not specify -sync, some X servers
may batch up several drawing operations together, producing a
less smooth effect. This is more likely to happen in
monochrome mode (on monochrome servers or when --mono is
specified).

--holdtime seconds
When the figure is complete, epicycle pauses this number of
seconds.

--linewidth N
Width in pixels of the body's track. Specifying values
greater than one may cause slower drawing. The fastest
value is usually zero, meaning one pixel.

--min_circles N
Smallest number of epicycles in the figure.

--max_circles N
Largest number of epicycles in the figure.

--min_speed number
Smallest possible value for the base speed of revolution of
the epicycles. The actual speeds of the epicycles vary from
this down to min_speed / harmonics.

--max_speed number
Smallest possible value for the base speed of revolution of
the epicycles.

--harmonics N
Number of possible harmonics; the larger this value is, the
greater the possible variety of possible speeds of epicycle.

--timestep number
Decreasing this value will reduce the distance the body moves
for each line segment, possibly producing a smoother figure.
Increasing it may produce faster results.

--divisor_poisson probability
Each epicycle rotates at a rate which is a factor of the base
speed. The speed of each epicycle is the base speed divided
by some integer between 1 and the value of the --harmonics
option. This integer is decided by starting at 1 and tossing
a biased coin. For each consecutive head, the value is
incremented by one. The integer will not be incremented
above the value of the --harmonics option. The argument of
this option decides the bias of the coin; it is the
probability that that coin will produce a head at any given
toss.

--size_factor_min number
Epicycles are always at least this factor smaller than their
parents.

--size_factor_max number
Epicycles are never more than this factor smaller than their
parents.

--fps Display the current frame rate and CPU load. --timestep
option multiplied by the timestepCoarseFactor resource. The
default value of 1 will almost always work fast enough and so
this resource is not available as a command-line option.

USER INTERFACE

The program runs mostly without user interaction. When running on
the root window, no input is accepted. When running in its own
window, the program will exit if mouse button 3 is pressed. If any
other mouse button is pressed, the current figure will be abandoned
and another will be started.

HISTORY

The geometry of epicycles was perfected by Hipparchus of Rhodes at
some time around 125 B.C., 185 years after the birth of Aristarchus
of Samos, the inventor of the heliocentric universe model.
Hipparchus applied epicycles to the Sun and the Moon. Ptolemy of
Alexandria went on to apply them to what was then the known universe,
at around 150 A.D. Copernicus went on to apply them to the
heliocentric model at the beginning of the sixteenth century.
Johannes Kepler discovered that the planets actually move in
elliptical orbits in about 1602. The inverse-square law of gravity
was suggested by Boulliau in 1645. Isaac Newton's Principia
Mathematica was published in 1687, and proved that Kepler's laws
derived from Newtonian gravitation.

BUGS

The colour selection is re-done for every figure. This may generate
too much network traffic for this program to work well over slow or
long links.

ENVIRONMENT

DISPLAY to get the default host and display number.

XENVIRONMENT
to get the name of a resource file that overrides the global
resources stored in the RESOURCE_MANAGER property.

XSCREENSAVER_WINDOW
The window ID to use with --root.

SEE ALSO

X(1), xscreensaver(1)

COPYRIGHT

Copyright (C) 1998, James Youngman. Permission to use, copy, modify,
distribute, and sell this software and its documentation for any
purpose is hereby granted without fee, provided that the above
copyright notice appear in all copies and that both that copyright
notice and this permission notice appear in supporting documentation.
No representations are made about the suitability of this software
for any purpose. It is provided "as is" without express or implied
warranty.

AUTHOR

James Youngman <jay@gnu.org>, April 1998.

X Version 11 6.09 (07-Jun-2024) epicycle(6)