### Rock Island | 🏝️

How it kinda works: (use the "step" slider to see this process 😃)
1. generate points in circle using poisson disc util Poisson- Disc Grow Patterns
2. grab group of points, make shapes
3. for each segment of shape, draw rectangle kind of shape upwards
4. use polygon util for clipping , draw from front to back Stars
5. use hatching for lighting

Thanks to @reinder for utils and help on this one!

```const turtle = new Turtle();
let polygons = new Polygons();

const step = 5; // min=1, max=5, step=1
const density = 8; // min=4, max=10, step=1
const shape = 15; // min=10, max=20, step=1
const radius = 500; // min=100, max=3000, step=100

const seed = 2;// min=2, max=200, step=1

let groups;
let points;
let random;

function init() {
random = new Random(seed);
groups = [];
polygons = new Polygons();
const takenPoints = [];
loop1: for (let p1 of points) {
if (takenPoints.indexOf(p1) < 0) {
var group = [];
loop2: for (let p2 of points) {
if (takenPoints.indexOf(p2) < 0) {
if (distance(p1, p2) < shape) {
group.push(p2);
if (takenPoints.indexOf(p1) < 0) {
takenPoints.push(p1);
}
takenPoints.push(p2);
if (group.length >= 10) {
break loop2;
}
}
}
}
if (group.length > 2) {
var mid = [0, 0];
for (let p of group) {
mid[0] += p[0];
mid[1] += p[1];
}
mid[0] /= group.length;
mid[1] /= group.length;
group.sort((a, b) => (angle(mid,a) - Math.PI) - (angle(mid,b) - Math.PI));

groups.push({group: group, mid:mid});
}
}
}

groups.sort((a, b) => a.mid[1] - b.mid[1]);
}

// let animation = 0; //min=0, max=1, step=0.01
function walk(i, anim) {
// if (anim === 1) anim = animation;

if (i == 0) init();

let _step = 1;
switch (step) {
case _step++: {
if (points[i][2]) {
turtle.jump(points[i]);
turtle.circle(0.4);
}
return i < points.length - 1;
}

case _step++: {
if (points[i][2]) {
turtle.jump(points[i]);
turtle.circle(0.4);
}
let g = groups.pop();
if (g != null) {
let group = g.group;
for (let j = 0; j < group.length; j++) {
let p1 = group[j];
let p2 = group[(j + 1) % group.length];

turtle.jump(p2[0], p2[1]);
turtle.goto(p1[0], p1[1]);
turtle.goto(p2[0], p2[1]);
}
let p = group[0];
turtle.goto(p[0], p[1]);
}
return groups.length > 0 || i < points.length - 1;
}
case _step++: {
let g = groups.pop();
if (g) {
let group = g.group;

let h = Math.min(distance([0, 0], group[0]) / (85), 1);
h = 1 - Math.pow(1 - h, 1 + random.next());
h = 1 - h;
h *= 100;
h += 3;

group.forEach(p => {
p[1] += 45;
p[1] /= 2;
});

for (let j = 0; j < group.length; j++) {
let p1 = group[j];
let p2 = group[(j + 1) % group.length];

turtle.jump(p2[0], p2[1]);
turtle.goto(p2[0], p2[1] - h);
turtle.goto(p1[0], p1[1] - h);
turtle.goto(p1[0], p1[1]);
turtle.goto(p2[0], p2[1]);
}
let p = group[0];
turtle.goto(p[0], p[1]);
}
return groups.length > 0;
}

case _step++:
case _step++: {
let g = groups.pop();
if (g ) {
let group = g.group;
if (g.mid[0]>-100 && g.mid[0]<100) {

let h = Math.min(distance([0, 0], group[0]) / (85), 1);
h = 1 - Math.pow(1 - h, 1 + random.next());
h -= (0.5 + Math.sin(groups.length + anim*Math.PI*2)/2) / 6 * (1-anim);
h = 1 - h;
h *= 100;
h += 3;

group.forEach(p => {
p[1] += 45;
p[1] /= 2;
});
const roofShape = polygons.create();
group.forEach((_, j) => roofShape.addPoints([group[j][0], group[j][1] - h]) );
polygons.draw(turtle, roofShape, true);

const segments = [];
group.forEach((_, i) => segments.push( [group[i], group[(i+1) % group.length]] ));
segments.sort( (s0, s1) => Math.max(s1[0][1], s1[1][1]) - Math.max(s0[0][1], s0[1][1]));
segments.forEach( segment => {
const p1 = segment[0];
const p2 = segment[1];

if ( p2[0]-p1[0] < 0 ) {
const shape = polygons.create();
[p2[0], p2[1]],
[p2[0], p2[1] - h],
[p1[0], p1[1] - h],
[p1[0], p1[1]],
[p2[0], p2[1]]
);

if (step > 4) {
const v = [p2[0] - p1[0], p2[1] - p1[1]];
const length = distance(v);
const normal = [v[1] / length, -v[0] / length];
let lightAngle = 2.1; // min=0, max=7, step=0.01
lightAngle += anim * Math.PI*2;
const lightDirection = [Math.sin(lightAngle), Math.cos(lightAngle)];
const diff = lightDirection[0] * normal[0] + lightDirection[1] * normal[1];
let hatching = 0.2 + (0.5 + diff * 0.5) * 2; // 0.2 - 2

// make light parts super light
if (hatching > 1.4) {
let d = (hatching - 1.4) * 2;
const ease = t => Math.pow(2, 10.0 * (t - 1.0));
hatching = hatching-0.5 + ease(d) * 0.5;
}
if (hatching < 9) {
}
}

polygons.draw(turtle, shape, true);
}
});

}
}
return groups.length > 0;
}
}
}

function modulo(i,  n) {
// positive modulo
return (n + (i % n)) % n;
}

const __EMPTY_ = [0,0];
function distance(p1, p2 = __EMPTY_) {
var delta = [p1[0] - p2[0], p1[1] - p2[1]];
return Math.sqrt(delta[0] * delta[0] + delta[1] * delta[1]);
}

function angle(a, b) {
return Math.atan2(a[1] - b[1], a[0] - b[0]);
}

// Seeded random - Mulberry32
function Random(seed) {
class Random {
constructor(seed) {
this.seed = seed;
}
next() {
var t = this.seed += 0x6D2B79F5;
t = Math.imul(t ^ t >>> 15, t | 1);
t ^= t + Math.imul(t ^ t >>> 7, t | 61);
return ((t ^ t >>> 14) >>> 0) / 4294967296;
}
shuffle(arr) {
for (let i = arr.length - 1; i > 0; i--) {
const j = Math.floor(this.next() * (i + 1));
[arr[i], arr[j]] = [arr[j], arr[i]];
}
return arr;
}
}
return new Random(seed);
}

// Forked from "Poisson- Disc Grow Patterns" by reinder
// https://turtletoy.net/turtle/b5510898dc

////////////////////////////////////////////////////////////////
// Poisson-Disc utility code. Created by Reinder Nijhoff 2019
// https://turtletoy.net/turtle/b5510898dc
////////////////////////////////////////////////////////////////
class PoissonDiscGrid {
this.cells = [];
sp.forEach( p => this.insert(p) );
}
insert(p) {
const x = p[0]*this.cellSize|0, y=p[1]*this.cellSize|0;
for (let xi = x-1; xi<=x+1; xi++) {
for (let yi = y-1; yi<=y+1; yi++) {
const ps = this.cell(xi,yi);
for (let i=0; i<ps.length; i++) {
if ((ps[i][0]-p[0])**2 + (ps[i][1]-p[1])**2 < this.radius2) {
return false;
}
}
}
}
this.cell(x, y).push(p);
return true;
}
cell(x,y) {
const c = this.cells;
return (c[x]?c[x]:c[x]=[])[y]?c[x][y]:c[x][y]=[];
}
}
class PoissonDisc {
this.result = [...sp];
this.active = [...sp];
this.random = random;
}
mainLoop: while (this.active.length > 0 && count > 0) {
const index = (this.random.next() * this.active.length * randomGrowOrder) | 0;
const point = this.active[index];
for (let i=0; i < maxTries; i++) {
const a = this.random.next() * 2 * Math.PI;
const d = (this.random.next()*loosePacking + 1) * radius;
const p = [point[0] + Math.cos(a)*d, point[1] + Math.sin(a)*d, point];
if (this.grid.insert(p)) {
this.result.push(p);
this.active.push(p);
count--;
continue mainLoop;
}
}
this.active.splice(index, 1);
}
return this.result;
}
}
}

////////////////////////////////////////////////////////////////
// Polygon Clipping utility code - Created by Reinder Nijhoff 2019
// https://turtletoy.net/turtle/a5befa1f8d
////////////////////////////////////////////////////////////////

function Polygons() {
const polygonList = [];
const Polygon = class {
constructor() {
this.cp = [];       // clip path: array of [x,y] pairs
this.dp = [];       // 2d lines [x0,y0],[x1,y1] to draw
this.aabb = [];     // AABB bounding box
}
// add point to clip path and update bounding box
let xmin = 1e5, xmax = -1e5, ymin = 1e5, ymax = -1e5;
(this.cp = [...this.cp, ...points]).forEach( p => {
xmin = Math.min(xmin, p[0]), xmax = Math.max(xmax, p[0]);
ymin = Math.min(ymin, p[1]), ymax = Math.max(ymax, p[1]);
});
this.aabb = [(xmin+xmax)/2, (ymin+ymax)/2, (xmax-xmin)/2, (ymax-ymin)/2];
}
// add segments (each a pair of points)
points.forEach(p => this.dp.push(p));
}
for (let i = 0, l = this.cp.length; i < l; i++) {
this.dp.push(this.cp[i], this.cp[(i + 1) % l]);
}
}
draw(t) {
for (let i = 0, l = this.dp.length; i < l; i+=2) {
t.jump(this.dp[i]), t.goto(this.dp[i + 1]);
}
}
const tp = new Polygon();
tp.cp.push([-1e5,-1e5],[1e5,-1e5],[1e5,1e5],[-1e5,1e5]);
const dx = Math.sin(a) * d,   dy = Math.cos(a) * d;
const cx = Math.sin(a) * 200, cy = Math.cos(a) * 200;
for (let i = 0.5; i < 150 / d; i++) {
tp.dp.push([dx * i + cy,   dy * i - cx], [dx * i - cy,   dy * i + cx]);
tp.dp.push([-dx * i + cy, -dy * i - cx], [-dx * i - cy, -dy * i + cx]);
}
tp.boolean(this, false);
this.dp = [...this.dp, ...tp.dp];
}
inside(p) {
let int = 0; // find number of i ntersection points from p to far away
for (let i = 0, l = this.cp.length; i < l; i++) {
if (this.segment_intersect(p, [0.1, -1000], this.cp[i], this.cp[(i + 1) % l])) {
int++;
}
}
return int & 1; // if even your outside
}
boolean(p, diff = true) {
// bouding box optimization by ge1doot.
if (Math.abs(this.aabb[0] - p.aabb[0]) - (p.aabb[2] + this.aabb[2]) >= 0 &&
Math.abs(this.aabb[1] - p.aabb[1]) - (p.aabb[3] + this.aabb[3]) >= 0) return this.dp.length > 0;

// polygon diff algorithm (narrow phase)
const ndp = [];
for (let i = 0, l = this.dp.length; i < l; i+=2) {
const ls0 = this.dp[i];
const ls1 = this.dp[i + 1];
// find all intersections with clip path
const int = [];
for (let j = 0, cl = p.cp.length; j < cl; j++) {
const pint = this.segment_intersect(ls0, ls1, p.cp[j], p.cp[(j + 1) % cl]);
if (pint !== false) {
int.push(pint);
}
}
if (int.length === 0) {
// 0 intersections, inside or outside?
if (diff === !p.inside(ls0)) {
ndp.push(ls0, ls1);
}
} else {
int.push(ls0, ls1);
// order intersection points on line ls.p1 to ls.p2
const cmpx = ls1[0] - ls0[0];
const cmpy = ls1[1] - ls0[1];
int.sort( (a,b) =>  (a[0] - ls0[0]) * cmpx + (a[1] - ls0[1]) * cmpy -
(b[0] - ls0[0]) * cmpx - (b[1] - ls0[1]) * cmpy);

for (let j = 0; j < int.length - 1; j++) {
if ((int[j][0] - int[j+1][0])**2 + (int[j][1] - int[j+1][1])**2 >= 0.001) {
if (diff === !p.inside([(int[j][0]+int[j+1][0])/2,(int[j][1]+int[j+1][1])/2])) {
ndp.push(int[j], int[j+1]);
}
}
}
}
}
return (this.dp = ndp).length > 0;
}
//port of http://paulbourke.net/geometry/pointlineplane/Helpers.cs
segment_intersect(l1p1, l1p2, l2p1, l2p2) {
const d   = (l2p2[1] - l2p1[1]) * (l1p2[0] - l1p1[0]) - (l2p2[0] - l2p1[0]) * (l1p2[1] - l1p1[1]);
if (d === 0) return false;
const n_a = (l2p2[0] - l2p1[0]) * (l1p1[1] - l2p1[1]) - (l2p2[1] - l2p1[1]) * (l1p1[0] - l2p1[0]);
const n_b = (l1p2[0] - l1p1[0]) * (l1p1[1] - l2p1[1]) - (l1p2[1] - l1p1[1]) * (l1p1[0] - l2p1[0]);
const ua = n_a / d;
const ub = n_b / d;
if (ua >= 0 && ua <= 1 && ub >= 0 && ub <= 1) {
return [l1p1[0] + ua * (l1p2[0] - l1p1[0]), l1p1[1] + ua * (l1p2[1] - l1p1[1])];
}
return false;
}
};
return {
list: () => polygonList,
create: () => new Polygon(),
draw: (turtle, p, addToVisList=true) => {
for (let j = 0; j < polygonList.length && p.boolean(polygonList[j]); j++);
p.draw(turtle);