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.