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Manpages XScreenSaverSection: User Commands (1)Updated: 27-Apr-97 Index Return to Main Contents NAMEepicycle - draws a point moving around a circle which moves around a cicle which...SYNOPSISepicycle [-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 probability] [-size_factor_min number] [-size_factor_max number]DESCRIPTIONThe 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
RESOURCES
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 command-line option. USER INTERFACEThe 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.HISTORYThe 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.BUGSThe 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.COPYRIGHTCopyright © 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.AUTHORJames Youngman <jay@gnu.org>, April 1998.
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