// You can find the Turtle API reference here: https://turtletoy.net/syntax
Canvas.setpenopacity(0.33);

// Global code will be evaluated once.
const turtle = new Turtle();
class Noise {
	// http://mrl.nyu.edu/~perlin/noise/
	constructor(octaves = 1) {
		this.p = new Uint8Array(512);
		this.octaves = octaves;
		for (let i = 0; i < 512; ++i) {
			this.p[i] = Math.random() * 256;
		}
	}
	lerp(t, a, b) {
		return a + t * (b - a);
	}
	grad2d(i, x, y) {
		const v = (i & 1) === 0 ? x : y;
		return (i & 2) === 0 ? -v : v;
	}
	noise2d(x2d, y2d) {
		const X = Math.floor(x2d) & 255;
		const Y = Math.floor(y2d) & 255;
		const x = x2d - Math.floor(x2d);
		const y = y2d - Math.floor(y2d);
		const fx = (3 - 2 * x) * x * x;
		const fy = (3 - 2 * y) * y * y;
		const p0 = this.p[X] + Y;
		const p1 = this.p[X + 1] + Y;
		return this.lerp(
			fy,
			this.lerp(
				fx,
				this.grad2d(this.p[p0], x, y),
				this.grad2d(this.p[p1], x - 1, y)
			),
			this.lerp(
				fx,
				this.grad2d(this.p[p0 + 1], x, y - 1),
				this.grad2d(this.p[p1 + 1], x - 1, y - 1)
			)
		);
	}
	noise(x, y) {
		let e = 1,
			k = 1,
			s = 0;
		for (let i = 0; i < this.octaves; ++i) {
			e *= 0.5;
			s += e * (1 + this.noise2d(k * x, k * y)) / 2;
			k *= 2;
		}
		return s;
	}
}
const perlin = new Noise(3);
// The walk function will be called until it returns false.
turtle.up();
function walk(i) {
    for (let j = -101; j < 100; j++) {
	    const h = perlin.noise(100 + j * 0.01, 100 + i * 0.01);
	    turtle.goto(j, 0.1 * i + h * 200 - 100);
	    turtle.down();
	}
    turtle.up();
    return i < 300;
}