What Is Best In Life #20: ZX Moire

Per Wikipedia, moiré fringes are the complex patterns that manifest as a result of interference between overlaid transparent images. Provided you don’t count people on TV with dodgy stripey shirts or ties then I first encountered them as attractive features on naive loading screens for early (1982-83) Spectrum games. Sometimes drawn by the BASIC loader. The canonical example (to my mind is this one):

zxmoire-draw1

Not sure, but I believe the pattern emerges as an artefact of the Spectrum’s line DRAW-ing algorithm. The progam I “wrote” just draws a straight line from the origin (bottom-left) to the right-hand side of the screen, then another to a point 2 pixels higher, etc (an opposite procedure is repeated to get the second section).

This same pattern is definitely also used on other early or graphically-limited systems though, so it is something that exists in the mathematical wilds of the real world. Its light/shade effect suggests 3D corridors, although I don’t think it was ever used as such on the Speccy. If you know differently then do tell!

zxmoire-draw2

As an aside, drawing CIRCLEs on top of each other with ever increasing radius also produced the good-of-the-gaps on the Speccy, though to a less impressive extent.

 

zxmoire-circle1

You can also see similar effects in real-life (as below, pinched from Wikipedia), the afore-mentioned clothing-unfit-for-TV (no example handy) or sometimes in a thumbnail image online (the pics on this post itself, most likely).

zxmoire-cage

In the midnight hour she cried moiré, moiré, moiré!

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One Comment Add yours

  1. Da22 says:

    Very interesting, never really looked into what that effect actually happened 👍

    Liked by 1 person

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