aUCBLogo Demos and Tests / mul4

to mul4
   ; ring with c groups of nrcol colors
   cS hT setSC 4 noRefresh setPS Se 2 2
   colors = se iseq 0 8 iseq 9 14
   nrcol=count colors
   m=0 alpha=-Pi/2 zwoPi=2*Pi r=280
   c=18 p=c*nrcol g=c*p*3
   if lessEqualP p nrcol [nrcol=p]
   ip=-int(p/2) zp=zwoPi/p zwoPig=zwoPi/g
   for [f 0 g-1]
   [   fzwoPig=f*zwoPig
      for [n 1 g-1]
      [   beta=(ip+mod m p)*zp
         ab=alpha+beta

         phi1=ab+fzwoPig
         x1=r*radCos phi1
         y1=r*radSin phi1

         phi2=ab+zwoPig*(mod n*f g)
         x2=r*radCos phi2
         y2=r*radSin phi2

         coords=fPut Se x1 y1 lPut Se x2 y2 []
         line coords Item (1+mod m nrcol) colors m=m+1
      ]
      updateGraph
      if key? [stop]
   ]
end