#!/usr/local/bin/yabasic
phase=0:delay=0.03
delta=PI/180
dim X(7), Y(7)
R=90:SX=3*R:SY=3*R
k=(SX-2*R)*0.5
OX=SX/2:OY=SY/2
clear screen
open window SX,SY
label loop
k$=inkey$(delay)
rem clear window
box k,k to SX-k,SY-k
circle OX,OY,R
gosub CalcCoord
gosub Trace
phase=phase+delta
 k=k+0.2*R*sin(phase*PI*3)
rem print k
if k$<>"q" then goto loop fi
close window
end

label CalcCoord
for i=1 to 5
X(i)=OX+R*sin(2*PI*(i-1)/5+phase)
Y(i)=OY-R*cos(2*PI*(i-1)/5+phase)
if Y(i)<0 then Y(i)=-Y(i) fi
next i
X(6)=X(1)
Y(6)=Y(1)
X(7)=X(2)
Y(7)=Y(2)
return

label Trace
for i=1 to 5
line X(i),Y(i) to X(i+2),Y(i+2)
next i
return