'Alien roses.sdlbas 2016-02-29 [B+=MGA] modified from
'a t and t line-art for sdlbasic (Windows, Unix etc etc)
' S Shaw, 2013 http://shawweb.myzen.co.uk/stephen/sdlbasic.htm
sq=740
SetDisplay(sq,sq,32,1)
autoback(-2)
scale=sq/2: ofs=sq/2
maxdist=(2*(ofs^2))^.5
n=4 : d=43 : flag=0
while 1
ink(rgb(0,128,0))
bar(0,0,sq,sq)
a=0 : a=a+d
newx=ofs : newy=ofs
while a>0.001
a=a+d
a=(a/360-INT(a/360))*360 : a=INT(a+0.0001)
X=n*a : X=(X/360-INT(X/360))*6.283185307
R=SIN (X)
T=a*0.0174532925
oldx=newx : oldy=newy
newx=R*SIN(T)*scale+ofs : newy=R*COS(T)*scale+ofs
' do not plot first line to reduce asymetry
flag=flag+1
if flag>1 then
leng=((oldy-newy)^2+(oldx-newx)^2)^.5
if leng<>0 then
dx = (newx-oldx)/leng
dy = (newy-oldy)/leng
for i=0 to leng
cc=255/.65*(((oldx+dx*i-ofs)^2+(oldy+dy*i-ofs)^2)^.5)/maxdist
ink(rgb(max(255-cc,0),min(255,cc),min(255,cc)))
fillcircle(oldx+dx*i,oldy+dy*i,3)
next
end if
end if
wend
ink(0)
text(0,0,16,"n= "+str(n)+" d="+str(d))
screenswap
wait(1800)
n+=2: if n>359 then : n=1 : end if
d+=1 : if d>359 then : d=1 : end if
newx=ofs : newy=ofs : flag=0
wend
