Erratic Turtle Graphics

Try it online @ catseye.tc | See also: Maze Clouds ∘ Latcarf ∘ Kolakoski Kurve

This is a gewgaw that I prototyped sometime in (I believe) 2018. I don't remember when I had the original idea, but I think it was not long before that.

And that idea is: turtle graphics, except there's a small margin of error. You might ask for "Turn right 90 degrees" but you might get only "Turn right 89.91 degrees".

If you use a faint pen, and repeat the drawing instructions many times over, you get a nice pencilly noisy effect.

In late 2019 I added a rudimentary command language similar to Logo, for user-created designs. The commands are:

fd NUM             move forward this many pixels
rt NUM             rotate right this many degrees
lt NUM             rotate left this many degrees
setxyr NUM NUM     set the coordinates, as a percentage of the
                   width and height of the canvas
shiftxyr NUM NUM   adjust the coordinates, as a percentage of the
                   width and height of the canvas
seterr NUM NUM     set the error rate for rotations and
                   movements respectively
shifterr NUM NUM   adjust the error rate for rotations and
                   movements respectively