cls
dim integer c(7)=(rgb(black),rgb(red),rgb(green),rgb(blue),rgb(yellow),rgb(magenta),rgb(cyan),0)

sw = 100  ' starting step width
px = MM.HRES - 10
py = MM.VRES - 10

page write 1

do
'  input "step size (1-800) (0=quit) ";sw
'  if sw = 0 then end

 cls
 i = 1
 t = timer
 for x1 = 10 to px step sw
   for x2 = 10 to px step sw
     line x1,10,x2,py,,c(i)
     i = i + 1
     if i > 5 then i = 1
   next x2
 next x1
 print @(10,0) sw "  ";
 page copy 1,0,B
 sw = sw - 1
 'pause 5000
 do : loop until timer - t > 800  ' try make constant time per step
loop until sw = 19
page write 0
end