Flash lag illusion

[tsh73]

So as Wikipedia says, eye/brain has some 80 ms lag - between something happened and you actually got it.
But how we can reflect flying balls?
Brain predicts where ball would be.

This program shows this lag. Run it with dt=500, see there are no tricks in the program
- red dot appears for single tact, in sync with green one
Now uncomment next line (dt=40)
I clearly see red light lags!

(Haha
I did it after few days of looking to Wikipedia article.
And so my colors are reversed and bullet is too big.
Anyway effect shows - thogh not as good as in Wikiperia animation.
)

'Flash lag illusion
'https://en.m.wikipedia.org/wiki/Flash_lag_illusion

nomainwin
open "Flash lag illusion" for graphics_nsb_nf as #gr
#gr "trapclose [quit]"
#gr "down; fill black; home; posxy cx cy"
dt=500  ' set dt to 500. You see red dot appears for single tact, in sync with green one
'dt=40   'now set dt smaller. I clearly see red light lags!
dx=10
s=10
x=0
xs=s*int(cx/s)

timer dt, [tick]

wait

[tick]
#gr "discard"
   #gr "place ";x;" ";cy
   #gr "backcolor black"
   #gr "boxfilled ";x+s;" ";cy+s
   if x=xs then
       #gr "place ";x;" ";cy+2*s
       #gr "backcolor black"
       #gr "boxfilled ";x+s;" ";cy+s+2*s
   end if
   x=x+s
   #gr "place ";x;" ";cy
   #gr "backcolor green"
   #gr "boxfilled ";x+s;" ";cy+s
   if x=xs then
       #gr "place ";x;" ";cy+2*s
       #gr "backcolor red"
       #gr "boxfilled ";x+s;" ";cy+s+2*s
   end if

   if x>2*cx then x = 0
   wait

[quit]
   timer 0
   close #gr
   end


[plus]

i had a bit of a conceptual lag in trying to figure out what was being demo'd here. Still trying to figure which part of code was drawing the supposedly lagging flasher. I was curious about the order of which was drawn first but I had more pressing things to do.