Bizarre effect (poor LCD screen required?)

With the recent news, I thought I’d have a look at getting to know floating point variables, and I came up with this. I was quite surprised, I’m not sure you’ll be able to see it if you have a super-duper screen, but depending on where you hold your head you might see either blurry colours, or well defined 3d bars. (Or even both at once, it makes me feel slightly queasy). Try tilting the screen or moving closer/further away.

ON ERROR : PRINT REPORT$;" at line ";ERL : END

CLS
MODE MODE
screen_width% = (VDU 11) << (VDU 4)
screen_height% = (VDU 12) << (VDU 5)

f = 10 / screen_width%
PROCplot_back_cosine
END

DEFPROCplot_back_cosine
  LOCAL I%, c
  FOR I% = 0 TO screen_width% - 1
    c = COS(2*PI*f*I%)
    IF c >= 0 THEN
      GCOL 0, 255 * c, 255 * (1 - c)
    ELSE
      GCOL 255 * -c , 0, 255 * (1 + c)
    ENDIF
    LINE I%, 0, I%, screen_height%
  NEXT
ENDPROC

I wrote it using 16M colours, but I found 256 works as well.

Thank you for posting the code. It looks great here at 3440 × 1440, although it feels slightly weird on the eyes. :)

I’m afraid what I see is exactly what I expected to see: a screen covered in vertical coloured stripes that don’t jump out as 3D to me, sorry. But I don’t have a poor LCD screen, it’s true: it’s a nice sharp 3840×2160 43" screen. Still looks the same from the far end of the room, only 4.5 m back, sorry.

But it’s bizarre, certainly. Looks like the side of a circus truck from the 1950s. Did they ban such paintwork because it was dangerously distracting, or did it just go out of fashion?

As Clive says, clear bars on a modest screen at 1600×900 (native res 1920×1080)

But there is a curious effect when moving my head in and out from 18" to 12" the bars get grow and shrink.