simple illusion

[tsh73]

nomainwin

notice "Illusion"+chr$(13)+_
"  So you draw squares."+chr$(13)+_
"Equal squares."+chr$(13)+_
"Black and white squares."+chr$(13)+_
"Staright squares on a stright line."+chr$(13)+_
" S L O W L Y."+chr$(13)+_
" Faster and faster."+chr$(13)+_
"  Wait!"+chr$(13)+_
"Just a second ago - "+chr$(13)+_
"It was staying in a sraight line?!"+chr$(13)+_
"*Illusion*"

sz=30

open "Illusion: parallel lines" for graphics_nsb_nf as #gr
#gr "home; down; posxy cx cy"
#gr "trapclose [quit]"

#gr "backcolor black"
p = 100
for j = 0 to 2*cx/sz
   y = j*sz
   d = ABS(((j+2) mod 4) - 2)    '01210 etc
   for x = 0 to 2*cx+2*sz step 2*sz
       xx=x+sz/3*d-2*sz
       #gr "place ";xx;" ";y
       #gr "boxfilled ";xx+sz;" ";y+sz
       #gr "place ";xx+sz;" ";y
       #gr "box ";xx+2*sz;" ";y+sz
       call pause p
       p = p-1
   next
next

#gr "flush"

wait

[quit]
   timer 0
   close #gr
   end

sub pause mil
   t0=time$("ms")
   while time$("ms") - t0 < mil
       scan
   wend
   exit sub
[quit]
   timer 0
   close #gr
   end
end sub