epicycle man page on DigitalUNIX

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XScreenSaver(1)						       XScreenSaver(1)

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

       epicycle	 [-display  host:display.screen]  [-root]  [-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  probabil‐
       ity] [-size_factor_min number] [-size_factor_max number]

       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.

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

       -root   Draw on the root 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 a private colormap for the window.

	       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

       -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

       -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

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

       Option		 Resource		Default Value
       ------		 --------		-------------
       -colors		 .colors		100
       -delay		 .delay			1000
       -holdtime	 .holdtime		2
       -linewidth	 .lineWidth		4
       -min_circles	 .minCircles		2
       -max_circles	 .maxCircles		10
       -min_speed	 .minSpeed		0.003
       -max_speed	 .maxSpeed		0.005
       -harmonics	 .harmonics		8
       -timestep	 .timestep		1.0
       -divisor_poisson	 .divisorPoisson	0.4
       -size_factor_min	 .sizeFactorMin		1.05
       -size_factor_max	 .sizeFactorMax		2.05
			 .timestepCoarseFactor	1.0
       Before the drawing of the figure is begun, a preliminary calculation of
       the  path is done in order to scale the radii of the epicycles so as to
       fit the figure on the screen or window.	For the sake  of  speed,  This
       calculation  is	done  with  a larger timestep than the actual drawing.
       The time-step used is the value of the -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 com‐
       mand-line option.

       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.

       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.

       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.

       Copyright  ©  1998,  James  Youngman.  Permission to use, copy, modify,
       distribute, and sell this software and its documentation for  any  pur‐
       pose  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 repre‐
       sentations are made about the suitability of this software for any pur‐
       pose.  It is provided "as is" without express or implied warranty.

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

X Version 11			   27-Apr-97		       XScreenSaver(1)

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