1epicycle(6x) XScreenSaver manual epicycle(6x)
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6 epicycle - draws a point moving around a circle which moves around a
7 cicle which...
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10 epicycle [-display host:display.screen] [-root] [-window] [-mono]
11 [-install] [-noinstall] [-visual viz] [-colors N] [-foreground name]
12 [-color-shift N] [-delay microseconds] [-holdtime seconds] [-linewidth
13 N] [-min_circles N] [-max_circles N] [-min_speed number] [-max_speed
14 number] [-harmonics N] [-timestep number] [-divisor_poisson probabil‐
15 ity] [-size_factor_min number] [-size_factor_max number]
16
18 The epicycle program draws the path traced out by a point on the edge
19 of a circle. That circle rotates around a point on the rim of another
20 circle, and so on, several times. The random curves produced can be
21 simple or complex, convex or concave, but they are always closed curves
22 (they never go in indefinitely).
23 You can configure both the way the curves are drawn and the way in
25 which the random sequence of circles is generated, either with command-
26 line options or X resources.
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29 -display host:display.screen
30 Specifies which X display we should use (see the section DIS‐
31 PLAY NAMES in X(1) for more information about this option).
32 -root Draw on the root window.
34 -window Draw on a newly-created window. This is the default.
36 -mono If on a color display, pretend we're on a monochrome display.
38 If we're on a mono display, we have no choice.
39 -install
41 Install a private colormap for the window.
42 -noinstall
44 Don't install a private colormap for the window.
45 -visual viz
47 Specify which visual to use. Legal values are the name of a
48 visual class, or the id number (decimal or hex) of a specific
49 visual. Possible choices include
50 default, best, mono, monochrome, gray, grey, color, staticgray,
52 staticcolor, truecolor, grayscale, greyscale, pseudocolor,
53 directcolor, number
54 If a decimal or hexadecimal number is used, XGetVisualInfo(3X)
56 is consulted to obtain the required visual.
57 -colors N
59 How many colors should be used (if possible). The colors are
60 chosen randomly.
61 -foreground name
63 With -mono, this option selects the foreground colour.
64 -delay microseconds
66 Specifies the delay between drawing successive line segments of
67 the path. If you do not specify -sync, some X servers may
68 batch up several drawing operations together, producing a less
69 smooth effect. This is more likely to happen in monochrome
70 mode (on monochrome servers or when -mono is specified).
71 -holdtime seconds
73 When the figure is complete, epicycle pauses this number of
74 seconds.
75 -linewidth N
77 Width in pixels of the body's track. Specifying values
78 greater than one may cause slower drawing. The fastest value
79 is usually zero, meaning one pixel.
80 -min_circles N
82 Smallest number of epicycles in the figure.
83 -max_circles N
85 Largest number of epicycles in the figure.
86 -min_speed number
88 Smallest possible value for the base speed of revolution of the
89 epicycles. The actual speeds of the epicycles vary from this
90 down to min_speed / harmonics.
91 -max_speed number
93 Smallest possible value for the base speed of revolution of the
94 epicycles.
95 -harmonics N
97 Number of possible harmonics; the larger this value is, the
98 greater the possible variety of possible speeds of epicycle.
99 -timestep number
101 Decreasing this value will reduce the distance the body moves
102 for each line segment, possibly producing a smoother figure.
103 Increasing it may produce faster results.
104 -divisor_poisson probability
106 Each epicycle rotates at a rate which is a factor of the base
107 speed. The speed of each epicycle is the base speed divided by
108 some integer between 1 and the value of the -harmonics option.
109 This integer is decided by starting at 1 and tossing a biased
110 coin. For each consecutive head, the value is incremented by
111 one. The integer will not be incremented above the value of
112 the -harmonics option. The argument of this option decides the
113 bias of the coin; it is the probability that that coin will
114 produce a head at any given toss.
115 -size_factor_min number
117 Epicycles are always at least this factor smaller than their
118 parents.
119 -size_factor_max number
121 Epicycles are never more than this factor smaller than their
122 parents.
123
125 Option Resource Default Value
126 ------ -------- -------------
127 -colors .colors 100
128 -delay .delay 1000
129 -holdtime .holdtime 2
130 -linewidth .lineWidth 4
131 -min_circles .minCircles 2
132 -max_circles .maxCircles 10
133 -min_speed .minSpeed 0.003
134 -max_speed .maxSpeed 0.005
135 -harmonics .harmonics 8
136 -timestep .timestep 1.0
137 -divisor_poisson .divisorPoisson 0.4
138 -size_factor_min .sizeFactorMin 1.05
139 -size_factor_max .sizeFactorMax 2.05
140 .timestepCoarseFactor 1.0
141 Before the drawing of the figure is begun, a preliminary calculation of
142 the path is done in order to scale the radii of the epicycles so as to
143 fit the figure on the screen or window. For the sake of speed, This
144 calculation is done with a larger timestep than the actual drawing.
145 The time-step used is the value of the -timestep option multiplied by
146 the timestepCoarseFactor resource. The default value of 1 will almost
147 always work fast enough and so this resource is not available as a com‐
148 mand-line option.
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151 The program runs mostly without user interaction. When running on the
152 root window, no input is accepted. When running in its own window, the
153 program will exit if mouse button 3 is pressed. If any other mouse
154 button is pressed, the current figure will be abandoned and another
155 will be started.
156
158 The geometry of epicycles was perfected by Hipparchus of Rhodes at some
159 time around 125 B.C., 185 years after the birth of Aristarchus of
160 Samos, the inventor of the heliocentric universe model. Hipparchus
161 applied epicycles to the Sun and the Moon. Ptolemy of Alexandria went
162 on to apply them to what was then the known universe, at around 150
163 A.D. Copernicus went on to apply them to the heliocentric model at the
164 beginning of the sixteenth century. Johannes Kepler discovered that
165 the planets actually move in elliptical orbits in about 1602. The
166 inverse-square law of gravity was suggested by Boulliau in 1645. Isaac
167 Newton's Principia Mathematica was published in 1687, and proved that
168 Kepler's laws derived from Newtonian gravitation.
169
171 The colour selection is re-done for every figure. This may generate
172 too much network traffic for this program to work well over slow or
173 long links.
174
176 Copyright © 1998, James Youngman. Permission to use, copy, modify,
177 distribute, and sell this software and its documentation for any pur‐
178 pose is hereby granted without fee, provided that the above copyright
179 notice appear in all copies and that both that copyright notice and
180 this permission notice appear in supporting documentation. No repre‐
181 sentations are made about the suitability of this software for any pur‐
182 pose. It is provided "as is" without express or implied warranty.
183
185 James Youngman <jay@gnu.org>, April 1998.
186X Version 11 5.05-3 (06-Apr-2008) epicycle(6x)