A basic spirograph, i.e., one circle rolling on another.

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// You can find the Turtle API reference here: https://turtletoy.net/syntax Canvas.setpenopacity(1); let r1 = 20; // min = 1, max = 100, step = 1 let r2 = 65; // min = 1, max = 100, step = 1 // rPen is the position on the second circle, it's a percentage of the radius. value > 100 are outside of the circle let rPen = 140; // min = 1, max = 200, step = 1 //const turns = 1; // min = 1, max = 50, step = 1 rPen /= 100; // Global code will be evaluated once. const turtle = new Turtle(); function getTurns(x, y){ let tmp = 0; if(y > x){ tmp = x; x = y; y = tmp; } let yy = y; let r = y; let rr = r; while(r != 0){ rr = r; r = x % yy; // console.log(x, yy, r, rr); x = yy; yy = r; } return y / rr; } let turns = getTurns(r1, r2); if(r1 > r2){ turns *= r2 * ((r2 + r1) / r1); } r1 /= 3; r2 /= 3; //console.log(turns); // The walk function will be called until it returns false. function walk(i) { let theta = Math.PI * i / 180; let cx = Math.cos(theta) * (r1 + r2); let cy = Math.sin(theta) * (r1 + r2); let rx = rPen * Math.cos(theta * (r2 + r1) / r1) * r2; let ry = rPen * Math.sin(theta * (r2 + r1) / r1) * r2; if(i) turtle.goto(cx + rx, cy + ry); else turtle.jump(cx + rx, cy + ry); return i <= 360 * turns; }