C Library Functions  - spirograph (3)

NAME
spirograph(3f) - [M_drawplus] draw a hypotrochoid (LICENSE:MIT)

CONTENTS

Synopsis
Description
Options
Example
Author
License

SYNOPSIS
subroutine spirograph(xcenter,ycenter,sunr0,planet0,offset0,radius,ilines,ang,angs,ifill) 

     real,intent(in)    :: xcenter, ycenter
     real,intent(in)    :: sunr0,planet0,offset0
     real,intent(in)    :: radius
     integer,intent(in) :: ilines
     real,intent(in)    :: ang
     real,intent(in)    :: angs
     integer,intent(in) :: ifill

DESCRIPTION
Draw a hypotrochoid generated by a fixed point on a circle rolling inside a fixed circle. It has the parametric equations 

      x = (R+r)costheta-(r+rho)cos((R+r)/rtheta)
      y = (R+r)sintheta-(r+rho)sin((R+r)/rtheta)
where R is the radius of the fixed circle, r is the radius of the rotating circle, and rho is the offset of the edge of the rotating circle. The figure closes only if R, r, and rho are rational. The equations can also be written

OPTIONS
xcenter,ycenter
  center of curve
sunr0 radii of sun, planet, and planet offset
planet0
  radii of sun, planet, and planet offset
offset0
  radii of sun, planet, and planet offset
radius radius to fit the shape to (no fit if radius is 0)
ilines number of points to sample along curve
ang angle to rotate the shape by, to orientate it.
angs angle to start sampling points at; ccw is +; 0 is East
ifill 1 make a filled polygon, 2 make a hatched polygon

EXAMPLE

AUTHOR
John S. Urban

LICENSE
MIT License

Nemo Release 3.1 spirograph (3) August 28, 2026
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