Pinna-Brelstaff

Pinna-Brelstaff, another #illusion:
1) Click on the image, to make it large
2) As you stare at the cross in the middle, move your head towards and away from your monitor repeatedly. The circles of rhombuses should be looking like they are moving while you do

google.com/search?q=Pinna-Brelstaff&source=lnms&tbm=isch

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function drawRhombus(x, y, w, r, innerAngle, rotation, mirror = false) {
    turtle.jump(x, y);
    if(mirror) { rotation = 112+rotation; innerAngle *= -1; }
    turtle.setheading(rotation);
    turtle.penup();
    turtle.backward(r);
    turtle.pendown();
    turtle.left(innerAngle / 2);
    turtle.forward(w);
    turtle.right(innerAngle);
    turtle.forward(w);
    // turtle.right(180 - innerAngle);
    // turtle.forward(w);
    // turtle.right(innerAngle);
    // turtle.forward(w);
}

Canvas.setpenopacity(.7);
const turtle = new Turtle();

turtle.jump(10, 0);
turtle.goto(-10, 0);
turtle.jump(0, 10);
turtle.goto(0, -10);

var sideLength = 7
r = Math.sqrt(sideLength * sideLength * 2);

// The walk function will be called until it returns false.
function walk(i) {
    var angle = (i / 18) * (Math.PI);
    var radius = 85;
    drawRhombus(radius * Math.sin(angle), radius * -Math.cos(angle), sideLength, r, 70, 35 + (i * 10));
    if(i < 30) {
        angle = (i * Math.PI) / 15;
        radius = 65;
        drawRhombus(radius * Math.sin(angle), radius * -Math.cos(angle), sideLength, r, 70, 35 + (i * 12), true);
    }
    return i < 36;
}