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 © 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.