add addzone and update zone in map-adapter interface

node_modules/earcut/LICENSE

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+ISC License
+
+Copyright (c) 2024, Mapbox
+
+Permission to use, copy, modify, and/or distribute this software for any purpose
+with or without fee is hereby granted, provided that the above copyright notice
+and this permission notice appear in all copies.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
+FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
+OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
+TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF
+THIS SOFTWARE.

node_modules/earcut/README.md

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+## Earcut
+
+The fastest and smallest JavaScript polygon triangulation library. 3KB gzipped.
+
+[![Node](https://github.com/mapbox/earcut/actions/workflows/node.yml/badge.svg)](https://github.com/mapbox/earcut/actions/workflows/node.yml)
+[![Average time to resolve an issue](http://isitmaintained.com/badge/resolution/mapbox/earcut.svg)](http://isitmaintained.com/project/mapbox/earcut "Average time to resolve an issue")
+[![Percentage of issues still open](http://isitmaintained.com/badge/open/mapbox/earcut.svg)](http://isitmaintained.com/project/mapbox/earcut "Percentage of issues still open")
+[![](https://img.shields.io/badge/simply-awesome-brightgreen.svg)](https://github.com/mourner/projects)
+
+#### The algorithm
+
+The library implements a modified ear slicing algorithm,
+optimized by [z-order curve](http://en.wikipedia.org/wiki/Z-order_curve) hashing
+and extended to handle holes, twisted polygons, degeneracies and self-intersections
+in a way that doesn't _guarantee_ correctness of triangulation,
+but attempts to always produce acceptable results for practical data.
+
+It's based on ideas from
+[FIST: Fast Industrial-Strength Triangulation of Polygons](http://www.cosy.sbg.ac.at/~held/projects/triang/triang.html) by Martin Held
+and [Triangulation by Ear Clipping](http://www.geometrictools.com/Documentation/TriangulationByEarClipping.pdf) by David Eberly.
+
+#### Why another triangulation library?
+
+The aim of this project is to create a JS triangulation library
+that is **fast enough for real-time triangulation in the browser**,
+sacrificing triangulation quality for raw speed and simplicity,
+while being robust enough to handle most practical datasets without crashing or producing garbage.
+Some benchmarks using Node 0.12:
+
+(ops/sec)         | pts  | earcut    | libtess  | poly2tri | pnltri    | polyk
+------------------| ---- | --------- | -------- | -------- | --------- | ------
+OSM building      | 15   | _795,935_ | _50,640_ | _61,501_ | _122,966_ | _175,570_
+dude shape        | 94   | _35,658_  | _10,339_ | _8,784_  | _11,172_  | _13,557_
+holed dude shape  | 104  | _28,319_  | _8,883_  | _7,494_  | _2,130_   | n/a
+complex OSM water | 2523 | _543_     | _77.54_  | failure  | failure   | n/a
+huge OSM water    | 5667 | _95_      | _29.30_  | failure  | failure   | n/a
+
+The original use case it was created for is [Mapbox GL](https://www.mapbox.com/mapbox-gl), WebGL-based interactive maps.
+
+If you want to get correct triangulation even on very bad data with lots of self-intersections
+and earcut is not precise enough, take a look at [libtess.js](https://github.com/brendankenny/libtess.js).
+
+#### Usage
+
+```js
+const triangles = earcut([10,0, 0,50, 60,60, 70,10]); // returns [1,0,3, 3,2,1]
+```
+
+Signature: `earcut(vertices[, holes, dimensions = 2])`.
+
+* `vertices` is a flat array of vertex coordinates like `[x0,y0, x1,y1, x2,y2, ...]`.
+* `holes` is an array of hole _indices_ if any
+  (e.g. `[5, 8]` for a 12-vertex input would mean one hole with vertices 5–7 and another with 8–11).
+* `dimensions` is the number of coordinates per vertex in the input array (`2` by default). Only two are used for triangulation (`x` and `y`), and the rest are ignored.
+
+Each group of three vertex indices in the resulting array forms a triangle.
+
+```js
+// triangulating a polygon with a hole
+earcut([0,0, 100,0, 100,100, 0,100,  20,20, 80,20, 80,80, 20,80], [4]);
+// [3,0,4, 5,4,0, 3,4,7, 5,0,1, 2,3,7, 6,5,1, 2,7,6, 6,1,2]
+
+// triangulating a polygon with 3d coords
+earcut([10,0,1, 0,50,2, 60,60,3, 70,10,4], null, 3);
+// [1,0,3, 3,2,1]
+```
+
+If you pass a single vertex as a hole, Earcut treats it as a Steiner point.
+
+Note that Earcut is a **2D** triangulation algorithm, and handles 3D data as if it was projected onto the XY plane (with Z component ignored).
+
+If your input is a multi-dimensional array (e.g. [GeoJSON Polygon](http://geojson.org/geojson-spec.html#polygon)),
+you can convert it to the format expected by Earcut with `earcut.flatten`:
+
+```js
+const data = earcut.flatten(geojson.geometry.coordinates);
+const triangles = earcut(data.vertices, data.holes, data.dimensions);
+```
+
+After getting a triangulation, you can verify its correctness with `earcut.deviation`:
+
+```js
+const deviation = earcut.deviation(vertices, holes, dimensions, triangles);
+```
+
+Returns the relative difference between the total area of triangles and the area of the input polygon.
+`0` means the triangulation is fully correct.
+
+#### Install
+
+Install with NPM: `npm install earcut`, then import as a module:
+
+```js
+import earcut from 'earcut';
+```
+
+Or use as a module directly in the browser with [jsDelivr](https://www.jsdelivr.com/esm):
+
+```html
+<script type="module">
+    import earcut from 'https://cdn.jsdelivr.net/npm/earcut/+esm';
+</script>
+```
+
+Alternatively, there's a UMD browser bundle with an `earcut` global variable (exposing the main function as `earcut.default`):
+
+```html
+<script src="https://cdn.jsdelivr.net/npm/earcut/dist/earcut.min.js"></script>
+```
+
+![](https://cloud.githubusercontent.com/assets/25395/5778431/e8ec0c10-9da3-11e4-8d4e-a2ced6a7d2b7.png)
+
+#### Ports to other languages
+
+- [mapbox/earcut.hpp](https://github.com/mapbox/earcut.hpp) (C++11)
+- [JaffaKetchup/dart_earcut](https://github.com/JaffaKetchup/dart_earcut) (Dart)
+- [earcut4j/earcut4j](https://github.com/earcut4j/earcut4j) (Java)
+- [the3deers/earcut-java](https://github.com/the3deers/earcut-java) (Java)
+- [Larpon/earcut](https://github.com/Larpon/earcut) (V)
+- [Cawfree/earcut-j](https://github.com/Cawfree/earcut-j) (Java, outdated)
+- [measuredweighed/SwiftEarcut](https://github.com/measuredweighed/SwiftEarcut) (Swift)

node_modules/earcut/dist/earcut.dev.js

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+(function (global, factory) {
+typeof exports === 'object' && typeof module !== 'undefined' ? factory(exports) :
+typeof define === 'function' && define.amd ? define(['exports'], factory) :
+(global = typeof globalThis !== 'undefined' ? globalThis : global || self, factory(global.earcut = {}));
+})(this, (function (exports) { 'use strict';
+
+function earcut(data, holeIndices, dim = 2) {
+
+    const hasHoles = holeIndices && holeIndices.length;
+    const outerLen = hasHoles ? holeIndices[0] * dim : data.length;
+    let outerNode = linkedList(data, 0, outerLen, dim, true);
+    const triangles = [];
+
+    if (!outerNode || outerNode.next === outerNode.prev) return triangles;
+
+    let minX, minY, invSize;
+
+    if (hasHoles) outerNode = eliminateHoles(data, holeIndices, outerNode, dim);
+
+    // if the shape is not too simple, we'll use z-order curve hash later; calculate polygon bbox
+    if (data.length > 80 * dim) {
+        minX = data[0];
+        minY = data[1];
+        let maxX = minX;
+        let maxY = minY;
+
+        for (let i = dim; i < outerLen; i += dim) {
+            const x = data[i];
+            const y = data[i + 1];
+            if (x < minX) minX = x;
+            if (y < minY) minY = y;
+            if (x > maxX) maxX = x;
+            if (y > maxY) maxY = y;
+        }
+
+        // minX, minY and invSize are later used to transform coords into integers for z-order calculation
+        invSize = Math.max(maxX - minX, maxY - minY);
+        invSize = invSize !== 0 ? 32767 / invSize : 0;
+    }
+
+    earcutLinked(outerNode, triangles, dim, minX, minY, invSize, 0);
+
+    return triangles;
+}
+
+// create a circular doubly linked list from polygon points in the specified winding order
+function linkedList(data, start, end, dim, clockwise) {
+    let last;
+
+    if (clockwise === (signedArea(data, start, end, dim) > 0)) {
+        for (let i = start; i < end; i += dim) last = insertNode(i / dim | 0, data[i], data[i + 1], last);
+    } else {
+        for (let i = end - dim; i >= start; i -= dim) last = insertNode(i / dim | 0, data[i], data[i + 1], last);
+    }
+
+    if (last && equals(last, last.next)) {
+        removeNode(last);
+        last = last.next;
+    }
+
+    return last;
+}
+
+// eliminate colinear or duplicate points
+function filterPoints(start, end) {
+    if (!start) return start;
+    if (!end) end = start;
+
+    let p = start,
+        again;
+    do {
+        again = false;
+
+        if (!p.steiner && (equals(p, p.next) || area(p.prev, p, p.next) === 0)) {
+            removeNode(p);
+            p = end = p.prev;
+            if (p === p.next) break;
+            again = true;
+
+        } else {
+            p = p.next;
+        }
+    } while (again || p !== end);
+
+    return end;
+}
+
+// main ear slicing loop which triangulates a polygon (given as a linked list)
+function earcutLinked(ear, triangles, dim, minX, minY, invSize, pass) {
+    if (!ear) return;
+
+    // interlink polygon nodes in z-order
+    if (!pass && invSize) indexCurve(ear, minX, minY, invSize);
+
+    let stop = ear;
+
+    // iterate through ears, slicing them one by one
+    while (ear.prev !== ear.next) {
+        const prev = ear.prev;
+        const next = ear.next;
+
+        if (invSize ? isEarHashed(ear, minX, minY, invSize) : isEar(ear)) {
+            triangles.push(prev.i, ear.i, next.i); // cut off the triangle
+
+            removeNode(ear);
+
+            // skipping the next vertex leads to less sliver triangles
+            ear = next.next;
+            stop = next.next;
+
+            continue;
+        }
+
+        ear = next;
+
+        // if we looped through the whole remaining polygon and can't find any more ears
+        if (ear === stop) {
+            // try filtering points and slicing again
+            if (!pass) {
+                earcutLinked(filterPoints(ear), triangles, dim, minX, minY, invSize, 1);
+
+            // if this didn't work, try curing all small self-intersections locally
+            } else if (pass === 1) {
+                ear = cureLocalIntersections(filterPoints(ear), triangles);
+                earcutLinked(ear, triangles, dim, minX, minY, invSize, 2);
+
+            // as a last resort, try splitting the remaining polygon into two
+            } else if (pass === 2) {
+                splitEarcut(ear, triangles, dim, minX, minY, invSize);
+            }
+
+            break;
+        }
+    }
+}
+
+// check whether a polygon node forms a valid ear with adjacent nodes
+function isEar(ear) {
+    const a = ear.prev,
+        b = ear,
+        c = ear.next;
+
+    if (area(a, b, c) >= 0) return false; // reflex, can't be an ear
+
+    // now make sure we don't have other points inside the potential ear
+    const ax = a.x, bx = b.x, cx = c.x, ay = a.y, by = b.y, cy = c.y;
+
+    // triangle bbox
+    const x0 = Math.min(ax, bx, cx),
+        y0 = Math.min(ay, by, cy),
+        x1 = Math.max(ax, bx, cx),
+        y1 = Math.max(ay, by, cy);
+
+    let p = c.next;
+    while (p !== a) {
+        if (p.x >= x0 && p.x <= x1 && p.y >= y0 && p.y <= y1 &&
+            pointInTriangleExceptFirst(ax, ay, bx, by, cx, cy, p.x, p.y) &&
+            area(p.prev, p, p.next) >= 0) return false;
+        p = p.next;
+    }
+
+    return true;
+}
+
+function isEarHashed(ear, minX, minY, invSize) {
+    const a = ear.prev,
+        b = ear,
+        c = ear.next;
+
+    if (area(a, b, c) >= 0) return false; // reflex, can't be an ear
+
+    const ax = a.x, bx = b.x, cx = c.x, ay = a.y, by = b.y, cy = c.y;
+
+    // triangle bbox
+    const x0 = Math.min(ax, bx, cx),
+        y0 = Math.min(ay, by, cy),
+        x1 = Math.max(ax, bx, cx),
+        y1 = Math.max(ay, by, cy);
+
+    // z-order range for the current triangle bbox;
+    const minZ = zOrder(x0, y0, minX, minY, invSize),
+        maxZ = zOrder(x1, y1, minX, minY, invSize);
+
+    let p = ear.prevZ,
+        n = ear.nextZ;
+
+    // look for points inside the triangle in both directions
+    while (p && p.z >= minZ && n && n.z <= maxZ) {
+        if (p.x >= x0 && p.x <= x1 && p.y >= y0 && p.y <= y1 && p !== a && p !== c &&
+            pointInTriangleExceptFirst(ax, ay, bx, by, cx, cy, p.x, p.y) && area(p.prev, p, p.next) >= 0) return false;
+        p = p.prevZ;
+
+        if (n.x >= x0 && n.x <= x1 && n.y >= y0 && n.y <= y1 && n !== a && n !== c &&
+            pointInTriangleExceptFirst(ax, ay, bx, by, cx, cy, n.x, n.y) && area(n.prev, n, n.next) >= 0) return false;
+        n = n.nextZ;
+    }
+
+    // look for remaining points in decreasing z-order
+    while (p && p.z >= minZ) {
+        if (p.x >= x0 && p.x <= x1 && p.y >= y0 && p.y <= y1 && p !== a && p !== c &&
+            pointInTriangleExceptFirst(ax, ay, bx, by, cx, cy, p.x, p.y) && area(p.prev, p, p.next) >= 0) return false;
+        p = p.prevZ;
+    }
+
+    // look for remaining points in increasing z-order
+    while (n && n.z <= maxZ) {
+        if (n.x >= x0 && n.x <= x1 && n.y >= y0 && n.y <= y1 && n !== a && n !== c &&
+            pointInTriangleExceptFirst(ax, ay, bx, by, cx, cy, n.x, n.y) && area(n.prev, n, n.next) >= 0) return false;
+        n = n.nextZ;
+    }
+
+    return true;
+}
+
+// go through all polygon nodes and cure small local self-intersections
+function cureLocalIntersections(start, triangles) {
+    let p = start;
+    do {
+        const a = p.prev,
+            b = p.next.next;
+
+        if (!equals(a, b) && intersects(a, p, p.next, b) && locallyInside(a, b) && locallyInside(b, a)) {
+
+            triangles.push(a.i, p.i, b.i);
+
+            // remove two nodes involved
+            removeNode(p);
+            removeNode(p.next);
+
+            p = start = b;
+        }
+        p = p.next;
+    } while (p !== start);
+
+    return filterPoints(p);
+}
+
+// try splitting polygon into two and triangulate them independently
+function splitEarcut(start, triangles, dim, minX, minY, invSize) {
+    // look for a valid diagonal that divides the polygon into two
+    let a = start;
+    do {
+        let b = a.next.next;
+        while (b !== a.prev) {
+            if (a.i !== b.i && isValidDiagonal(a, b)) {
+                // split the polygon in two by the diagonal
+                let c = splitPolygon(a, b);
+
+                // filter colinear points around the cuts
+                a = filterPoints(a, a.next);
+                c = filterPoints(c, c.next);
+
+                // run earcut on each half
+                earcutLinked(a, triangles, dim, minX, minY, invSize, 0);
+                earcutLinked(c, triangles, dim, minX, minY, invSize, 0);
+                return;
+            }
+            b = b.next;
+        }
+        a = a.next;
+    } while (a !== start);
+}
+
+// link every hole into the outer loop, producing a single-ring polygon without holes
+function eliminateHoles(data, holeIndices, outerNode, dim) {
+    const queue = [];
+
+    for (let i = 0, len = holeIndices.length; i < len; i++) {
+        const start = holeIndices[i] * dim;
+        const end = i < len - 1 ? holeIndices[i + 1] * dim : data.length;
+        const list = linkedList(data, start, end, dim, false);
+        if (list === list.next) list.steiner = true;
+        queue.push(getLeftmost(list));
+    }
+
+    queue.sort(compareXYSlope);
+
+    // process holes from left to right
+    for (let i = 0; i < queue.length; i++) {
+        outerNode = eliminateHole(queue[i], outerNode);
+    }
+
+    return outerNode;
+}
+
+function compareXYSlope(a, b) {
+    let result = a.x - b.x;
+    // when the left-most point of 2 holes meet at a vertex, sort the holes counterclockwise so that when we find
+    // the bridge to the outer shell is always the point that they meet at.
+    if (result === 0) {
+        result = a.y - b.y;
+        if (result === 0) {
+            const aSlope = (a.next.y - a.y) / (a.next.x - a.x);
+            const bSlope = (b.next.y - b.y) / (b.next.x - b.x);
+            result = aSlope - bSlope;
+        }
+    }
+    return result;
+}
+
+// find a bridge between vertices that connects hole with an outer ring and link it
+function eliminateHole(hole, outerNode) {
+    const bridge = findHoleBridge(hole, outerNode);
+    if (!bridge) {
+        return outerNode;
+    }
+
+    const bridgeReverse = splitPolygon(bridge, hole);
+
+    // filter collinear points around the cuts
+    filterPoints(bridgeReverse, bridgeReverse.next);
+    return filterPoints(bridge, bridge.next);
+}
+
+// David Eberly's algorithm for finding a bridge between hole and outer polygon
+function findHoleBridge(hole, outerNode) {
+    let p = outerNode;
+    const hx = hole.x;
+    const hy = hole.y;
+    let qx = -Infinity;
+    let m;
+
+    // find a segment intersected by a ray from the hole's leftmost point to the left;
+    // segment's endpoint with lesser x will be potential connection point
+    // unless they intersect at a vertex, then choose the vertex
+    if (equals(hole, p)) return p;
+    do {
+        if (equals(hole, p.next)) return p.next;
+        else if (hy <= p.y && hy >= p.next.y && p.next.y !== p.y) {
+            const x = p.x + (hy - p.y) * (p.next.x - p.x) / (p.next.y - p.y);
+            if (x <= hx && x > qx) {
+                qx = x;
+                m = p.x < p.next.x ? p : p.next;
+                if (x === hx) return m; // hole touches outer segment; pick leftmost endpoint
+            }
+        }
+        p = p.next;
+    } while (p !== outerNode);
+
+    if (!m) return null;
+
+    // look for points inside the triangle of hole point, segment intersection and endpoint;
+    // if there are no points found, we have a valid connection;
+    // otherwise choose the point of the minimum angle with the ray as connection point
+
+    const stop = m;
+    const mx = m.x;
+    const my = m.y;
+    let tanMin = Infinity;
+
+    p = m;
+
+    do {
+        if (hx >= p.x && p.x >= mx && hx !== p.x &&
+                pointInTriangle(hy < my ? hx : qx, hy, mx, my, hy < my ? qx : hx, hy, p.x, p.y)) {
+
+            const tan = Math.abs(hy - p.y) / (hx - p.x); // tangential
+
+            if (locallyInside(p, hole) &&
+                (tan < tanMin || (tan === tanMin && (p.x > m.x || (p.x === m.x && sectorContainsSector(m, p)))))) {
+                m = p;
+                tanMin = tan;
+            }
+        }
+
+        p = p.next;
+    } while (p !== stop);
+
+    return m;
+}
+
+// whether sector in vertex m contains sector in vertex p in the same coordinates
+function sectorContainsSector(m, p) {
+    return area(m.prev, m, p.prev) < 0 && area(p.next, m, m.next) < 0;
+}
+
+// interlink polygon nodes in z-order
+function indexCurve(start, minX, minY, invSize) {
+    let p = start;
+    do {
+        if (p.z === 0) p.z = zOrder(p.x, p.y, minX, minY, invSize);
+        p.prevZ = p.prev;
+        p.nextZ = p.next;
+        p = p.next;
+    } while (p !== start);
+
+    p.prevZ.nextZ = null;
+    p.prevZ = null;
+
+    sortLinked(p);
+}
+
+// Simon Tatham's linked list merge sort algorithm
+// http://www.chiark.greenend.org.uk/~sgtatham/algorithms/listsort.html
+function sortLinked(list) {
+    let numMerges;
+    let inSize = 1;
+
+    do {
+        let p = list;
+        let e;
+        list = null;
+        let tail = null;
+        numMerges = 0;
+
+        while (p) {
+            numMerges++;
+            let q = p;
+            let pSize = 0;
+            for (let i = 0; i < inSize; i++) {
+                pSize++;
+                q = q.nextZ;
+                if (!q) break;
+            }
+            let qSize = inSize;
+
+            while (pSize > 0 || (qSize > 0 && q)) {
+
+                if (pSize !== 0 && (qSize === 0 || !q || p.z <= q.z)) {
+                    e = p;
+                    p = p.nextZ;
+                    pSize--;
+                } else {
+                    e = q;
+                    q = q.nextZ;
+                    qSize--;
+                }
+
+                if (tail) tail.nextZ = e;
+                else list = e;
+
+                e.prevZ = tail;
+                tail = e;
+            }
+
+            p = q;
+        }
+
+        tail.nextZ = null;
+        inSize *= 2;
+
+    } while (numMerges > 1);
+
+    return list;
+}
+
+// z-order of a point given coords and inverse of the longer side of data bbox
+function zOrder(x, y, minX, minY, invSize) {
+    // coords are transformed into non-negative 15-bit integer range
+    x = (x - minX) * invSize | 0;
+    y = (y - minY) * invSize | 0;
+
+    x = (x | (x << 8)) & 0x00FF00FF;
+    x = (x | (x << 4)) & 0x0F0F0F0F;
+    x = (x | (x << 2)) & 0x33333333;
+    x = (x | (x << 1)) & 0x55555555;
+
+    y = (y | (y << 8)) & 0x00FF00FF;
+    y = (y | (y << 4)) & 0x0F0F0F0F;
+    y = (y | (y << 2)) & 0x33333333;
+    y = (y | (y << 1)) & 0x55555555;
+
+    return x | (y << 1);
+}
+
+// find the leftmost node of a polygon ring
+function getLeftmost(start) {
+    let p = start,
+        leftmost = start;
+    do {
+        if (p.x < leftmost.x || (p.x === leftmost.x && p.y < leftmost.y)) leftmost = p;
+        p = p.next;
+    } while (p !== start);
+
+    return leftmost;
+}
+
+// check if a point lies within a convex triangle
+function pointInTriangle(ax, ay, bx, by, cx, cy, px, py) {
+    return (cx - px) * (ay - py) >= (ax - px) * (cy - py) &&
+           (ax - px) * (by - py) >= (bx - px) * (ay - py) &&
+           (bx - px) * (cy - py) >= (cx - px) * (by - py);
+}
+
+// check if a point lies within a convex triangle but false if its equal to the first point of the triangle
+function pointInTriangleExceptFirst(ax, ay, bx, by, cx, cy, px, py) {
+    return !(ax === px && ay === py) && pointInTriangle(ax, ay, bx, by, cx, cy, px, py);
+}
+
+// check if a diagonal between two polygon nodes is valid (lies in polygon interior)
+function isValidDiagonal(a, b) {
+    return a.next.i !== b.i && a.prev.i !== b.i && !intersectsPolygon(a, b) && // doesn't intersect other edges
+           (locallyInside(a, b) && locallyInside(b, a) && middleInside(a, b) && // locally visible
+            (area(a.prev, a, b.prev) || area(a, b.prev, b)) || // does not create opposite-facing sectors
+            equals(a, b) && area(a.prev, a, a.next) > 0 && area(b.prev, b, b.next) > 0); // special zero-length case
+}
+
+// signed area of a triangle
+function area(p, q, r) {
+    return (q.y - p.y) * (r.x - q.x) - (q.x - p.x) * (r.y - q.y);
+}
+
+// check if two points are equal
+function equals(p1, p2) {
+    return p1.x === p2.x && p1.y === p2.y;
+}
+
+// check if two segments intersect
+function intersects(p1, q1, p2, q2) {
+    const o1 = sign(area(p1, q1, p2));
+    const o2 = sign(area(p1, q1, q2));
+    const o3 = sign(area(p2, q2, p1));
+    const o4 = sign(area(p2, q2, q1));
+
+    if (o1 !== o2 && o3 !== o4) return true; // general case
+
+    if (o1 === 0 && onSegment(p1, p2, q1)) return true; // p1, q1 and p2 are collinear and p2 lies on p1q1
+    if (o2 === 0 && onSegment(p1, q2, q1)) return true; // p1, q1 and q2 are collinear and q2 lies on p1q1
+    if (o3 === 0 && onSegment(p2, p1, q2)) return true; // p2, q2 and p1 are collinear and p1 lies on p2q2
+    if (o4 === 0 && onSegment(p2, q1, q2)) return true; // p2, q2 and q1 are collinear and q1 lies on p2q2
+
+    return false;
+}
+
+// for collinear points p, q, r, check if point q lies on segment pr
+function onSegment(p, q, r) {
+    return q.x <= Math.max(p.x, r.x) && q.x >= Math.min(p.x, r.x) && q.y <= Math.max(p.y, r.y) && q.y >= Math.min(p.y, r.y);
+}
+
+function sign(num) {
+    return num > 0 ? 1 : num < 0 ? -1 : 0;
+}
+
+// check if a polygon diagonal intersects any polygon segments
+function intersectsPolygon(a, b) {
+    let p = a;
+    do {
+        if (p.i !== a.i && p.next.i !== a.i && p.i !== b.i && p.next.i !== b.i &&
+                intersects(p, p.next, a, b)) return true;
+        p = p.next;
+    } while (p !== a);
+
+    return false;
+}
+
+// check if a polygon diagonal is locally inside the polygon
+function locallyInside(a, b) {
+    return area(a.prev, a, a.next) < 0 ?
+        area(a, b, a.next) >= 0 && area(a, a.prev, b) >= 0 :
+        area(a, b, a.prev) < 0 || area(a, a.next, b) < 0;
+}
+
+// check if the middle point of a polygon diagonal is inside the polygon
+function middleInside(a, b) {
+    let p = a;
+    let inside = false;
+    const px = (a.x + b.x) / 2;
+    const py = (a.y + b.y) / 2;
+    do {
+        if (((p.y > py) !== (p.next.y > py)) && p.next.y !== p.y &&
+                (px < (p.next.x - p.x) * (py - p.y) / (p.next.y - p.y) + p.x))
+            inside = !inside;
+        p = p.next;
+    } while (p !== a);
+
+    return inside;
+}
+
+// link two polygon vertices with a bridge; if the vertices belong to the same ring, it splits polygon into two;
+// if one belongs to the outer ring and another to a hole, it merges it into a single ring
+function splitPolygon(a, b) {
+    const a2 = createNode(a.i, a.x, a.y),
+        b2 = createNode(b.i, b.x, b.y),
+        an = a.next,
+        bp = b.prev;
+
+    a.next = b;
+    b.prev = a;
+
+    a2.next = an;
+    an.prev = a2;
+
+    b2.next = a2;
+    a2.prev = b2;
+
+    bp.next = b2;
+    b2.prev = bp;
+
+    return b2;
+}
+
+// create a node and optionally link it with previous one (in a circular doubly linked list)
+function insertNode(i, x, y, last) {
+    const p = createNode(i, x, y);
+
+    if (!last) {
+        p.prev = p;
+        p.next = p;
+
+    } else {
+        p.next = last.next;
+        p.prev = last;
+        last.next.prev = p;
+        last.next = p;
+    }
+    return p;
+}
+
+function removeNode(p) {
+    p.next.prev = p.prev;
+    p.prev.next = p.next;
+
+    if (p.prevZ) p.prevZ.nextZ = p.nextZ;
+    if (p.nextZ) p.nextZ.prevZ = p.prevZ;
+}
+
+function createNode(i, x, y) {
+    return {
+        i, // vertex index in coordinates array
+        x, y, // vertex coordinates
+        prev: null, // previous and next vertex nodes in a polygon ring
+        next: null,
+        z: 0, // z-order curve value
+        prevZ: null, // previous and next nodes in z-order
+        nextZ: null,
+        steiner: false // indicates whether this is a steiner point
+    };
+}
+
+// return a percentage difference between the polygon area and its triangulation area;
+// used to verify correctness of triangulation
+function deviation(data, holeIndices, dim, triangles) {
+    const hasHoles = holeIndices && holeIndices.length;
+    const outerLen = hasHoles ? holeIndices[0] * dim : data.length;
+
+    let polygonArea = Math.abs(signedArea(data, 0, outerLen, dim));
+    if (hasHoles) {
+        for (let i = 0, len = holeIndices.length; i < len; i++) {
+            const start = holeIndices[i] * dim;
+            const end = i < len - 1 ? holeIndices[i + 1] * dim : data.length;
+            polygonArea -= Math.abs(signedArea(data, start, end, dim));
+        }
+    }
+
+    let trianglesArea = 0;
+    for (let i = 0; i < triangles.length; i += 3) {
+        const a = triangles[i] * dim;
+        const b = triangles[i + 1] * dim;
+        const c = triangles[i + 2] * dim;
+        trianglesArea += Math.abs(
+            (data[a] - data[c]) * (data[b + 1] - data[a + 1]) -
+            (data[a] - data[b]) * (data[c + 1] - data[a + 1]));
+    }
+
+    return polygonArea === 0 && trianglesArea === 0 ? 0 :
+        Math.abs((trianglesArea - polygonArea) / polygonArea);
+}
+
+function signedArea(data, start, end, dim) {
+    let sum = 0;
+    for (let i = start, j = end - dim; i < end; i += dim) {
+        sum += (data[j] - data[i]) * (data[i + 1] + data[j + 1]);
+        j = i;
+    }
+    return sum;
+}
+
+// turn a polygon in a multi-dimensional array form (e.g. as in GeoJSON) into a form Earcut accepts
+function flatten(data) {
+    const vertices = [];
+    const holes = [];
+    const dimensions = data[0][0].length;
+    let holeIndex = 0;
+    let prevLen = 0;
+
+    for (const ring of data) {
+        for (const p of ring) {
+            for (let d = 0; d < dimensions; d++) vertices.push(p[d]);
+        }
+        if (prevLen) {
+            holeIndex += prevLen;
+            holes.push(holeIndex);
+        }
+        prevLen = ring.length;
+    }
+    return {vertices, holes, dimensions};
+}
+
+exports.default = earcut;
+exports.deviation = deviation;
+exports.flatten = flatten;
+
+Object.defineProperty(exports, '__esModule', { value: true });
+
+}));

node_modules/earcut/package.json

@@ -0,0 +1,40 @@
+{
+  "name": "earcut",
+  "version": "3.0.2",
+  "description": "The fastest and smallest JavaScript polygon triangulation library for your WebGL apps",
+  "main": "src/earcut.js",
+  "type": "module",
+  "exports": "./src/earcut.js",
+  "files": [
+    "src/earcut.js",
+    "dist/earcut.min.js",
+    "dist/earcut.dev.js"
+  ],
+  "scripts": {
+    "pretest": "eslint src test/test.js bench/*.js viz/viz.js",
+    "test": "node --test",
+    "build": "rollup -c",
+    "prepublishOnly": "npm run build",
+    "cov": "node --test --experimental-test-coverage"
+  },
+  "author": "Vladimir Agafonkin",
+  "license": "ISC",
+  "devDependencies": {
+    "@rollup/plugin-terser": "^0.4.4",
+    "benchmark": "^2.1.4",
+    "eslint": "^9.31.0",
+    "eslint-config-mourner": "^4.1.0",
+    "rollup": "^4.45.1"
+  },
+  "eslintConfig": {
+    "extends": "mourner",
+    "parserOptions": {
+      "sourceType": "module",
+      "ecmaVersion": 2020
+    }
+  },
+  "repository": {
+    "type": "git",
+    "url": "git://github.com/mapbox/earcut.git"
+  }
+}

node_modules/earcut/src/earcut.js

@@ -0,0 +1,682 @@
+
+export default function earcut(data, holeIndices, dim = 2) {
+
+    const hasHoles = holeIndices && holeIndices.length;
+    const outerLen = hasHoles ? holeIndices[0] * dim : data.length;
+    let outerNode = linkedList(data, 0, outerLen, dim, true);
+    const triangles = [];
+
+    if (!outerNode || outerNode.next === outerNode.prev) return triangles;
+
+    let minX, minY, invSize;
+
+    if (hasHoles) outerNode = eliminateHoles(data, holeIndices, outerNode, dim);
+
+    // if the shape is not too simple, we'll use z-order curve hash later; calculate polygon bbox
+    if (data.length > 80 * dim) {
+        minX = data[0];
+        minY = data[1];
+        let maxX = minX;
+        let maxY = minY;
+
+        for (let i = dim; i < outerLen; i += dim) {
+            const x = data[i];
+            const y = data[i + 1];
+            if (x < minX) minX = x;
+            if (y < minY) minY = y;
+            if (x > maxX) maxX = x;
+            if (y > maxY) maxY = y;
+        }
+
+        // minX, minY and invSize are later used to transform coords into integers for z-order calculation
+        invSize = Math.max(maxX - minX, maxY - minY);
+        invSize = invSize !== 0 ? 32767 / invSize : 0;
+    }
+
+    earcutLinked(outerNode, triangles, dim, minX, minY, invSize, 0);
+
+    return triangles;
+}
+
+// create a circular doubly linked list from polygon points in the specified winding order
+function linkedList(data, start, end, dim, clockwise) {
+    let last;
+
+    if (clockwise === (signedArea(data, start, end, dim) > 0)) {
+        for (let i = start; i < end; i += dim) last = insertNode(i / dim | 0, data[i], data[i + 1], last);
+    } else {
+        for (let i = end - dim; i >= start; i -= dim) last = insertNode(i / dim | 0, data[i], data[i + 1], last);
+    }
+
+    if (last && equals(last, last.next)) {
+        removeNode(last);
+        last = last.next;
+    }
+
+    return last;
+}
+
+// eliminate colinear or duplicate points
+function filterPoints(start, end) {
+    if (!start) return start;
+    if (!end) end = start;
+
+    let p = start,
+        again;
+    do {
+        again = false;
+
+        if (!p.steiner && (equals(p, p.next) || area(p.prev, p, p.next) === 0)) {
+            removeNode(p);
+            p = end = p.prev;
+            if (p === p.next) break;
+            again = true;
+
+        } else {
+            p = p.next;
+        }
+    } while (again || p !== end);
+
+    return end;
+}
+
+// main ear slicing loop which triangulates a polygon (given as a linked list)
+function earcutLinked(ear, triangles, dim, minX, minY, invSize, pass) {
+    if (!ear) return;
+
+    // interlink polygon nodes in z-order
+    if (!pass && invSize) indexCurve(ear, minX, minY, invSize);
+
+    let stop = ear;
+
+    // iterate through ears, slicing them one by one
+    while (ear.prev !== ear.next) {
+        const prev = ear.prev;
+        const next = ear.next;
+
+        if (invSize ? isEarHashed(ear, minX, minY, invSize) : isEar(ear)) {
+            triangles.push(prev.i, ear.i, next.i); // cut off the triangle
+
+            removeNode(ear);
+
+            // skipping the next vertex leads to less sliver triangles
+            ear = next.next;
+            stop = next.next;
+
+            continue;
+        }
+
+        ear = next;
+
+        // if we looped through the whole remaining polygon and can't find any more ears
+        if (ear === stop) {
+            // try filtering points and slicing again
+            if (!pass) {
+                earcutLinked(filterPoints(ear), triangles, dim, minX, minY, invSize, 1);
+
+            // if this didn't work, try curing all small self-intersections locally
+            } else if (pass === 1) {
+                ear = cureLocalIntersections(filterPoints(ear), triangles);
+                earcutLinked(ear, triangles, dim, minX, minY, invSize, 2);
+
+            // as a last resort, try splitting the remaining polygon into two
+            } else if (pass === 2) {
+                splitEarcut(ear, triangles, dim, minX, minY, invSize);
+            }
+
+            break;
+        }
+    }
+}
+
+// check whether a polygon node forms a valid ear with adjacent nodes
+function isEar(ear) {
+    const a = ear.prev,
+        b = ear,
+        c = ear.next;
+
+    if (area(a, b, c) >= 0) return false; // reflex, can't be an ear
+
+    // now make sure we don't have other points inside the potential ear
+    const ax = a.x, bx = b.x, cx = c.x, ay = a.y, by = b.y, cy = c.y;
+
+    // triangle bbox
+    const x0 = Math.min(ax, bx, cx),
+        y0 = Math.min(ay, by, cy),
+        x1 = Math.max(ax, bx, cx),
+        y1 = Math.max(ay, by, cy);
+
+    let p = c.next;
+    while (p !== a) {
+        if (p.x >= x0 && p.x <= x1 && p.y >= y0 && p.y <= y1 &&
+            pointInTriangleExceptFirst(ax, ay, bx, by, cx, cy, p.x, p.y) &&
+            area(p.prev, p, p.next) >= 0) return false;
+        p = p.next;
+    }
+
+    return true;
+}
+
+function isEarHashed(ear, minX, minY, invSize) {
+    const a = ear.prev,
+        b = ear,
+        c = ear.next;
+
+    if (area(a, b, c) >= 0) return false; // reflex, can't be an ear
+
+    const ax = a.x, bx = b.x, cx = c.x, ay = a.y, by = b.y, cy = c.y;
+
+    // triangle bbox
+    const x0 = Math.min(ax, bx, cx),
+        y0 = Math.min(ay, by, cy),
+        x1 = Math.max(ax, bx, cx),
+        y1 = Math.max(ay, by, cy);
+
+    // z-order range for the current triangle bbox;
+    const minZ = zOrder(x0, y0, minX, minY, invSize),
+        maxZ = zOrder(x1, y1, minX, minY, invSize);
+
+    let p = ear.prevZ,
+        n = ear.nextZ;
+
+    // look for points inside the triangle in both directions
+    while (p && p.z >= minZ && n && n.z <= maxZ) {
+        if (p.x >= x0 && p.x <= x1 && p.y >= y0 && p.y <= y1 && p !== a && p !== c &&
+            pointInTriangleExceptFirst(ax, ay, bx, by, cx, cy, p.x, p.y) && area(p.prev, p, p.next) >= 0) return false;
+        p = p.prevZ;
+
+        if (n.x >= x0 && n.x <= x1 && n.y >= y0 && n.y <= y1 && n !== a && n !== c &&
+            pointInTriangleExceptFirst(ax, ay, bx, by, cx, cy, n.x, n.y) && area(n.prev, n, n.next) >= 0) return false;
+        n = n.nextZ;
+    }
+
+    // look for remaining points in decreasing z-order
+    while (p && p.z >= minZ) {
+        if (p.x >= x0 && p.x <= x1 && p.y >= y0 && p.y <= y1 && p !== a && p !== c &&
+            pointInTriangleExceptFirst(ax, ay, bx, by, cx, cy, p.x, p.y) && area(p.prev, p, p.next) >= 0) return false;
+        p = p.prevZ;
+    }
+
+    // look for remaining points in increasing z-order
+    while (n && n.z <= maxZ) {
+        if (n.x >= x0 && n.x <= x1 && n.y >= y0 && n.y <= y1 && n !== a && n !== c &&
+            pointInTriangleExceptFirst(ax, ay, bx, by, cx, cy, n.x, n.y) && area(n.prev, n, n.next) >= 0) return false;
+        n = n.nextZ;
+    }
+
+    return true;
+}
+
+// go through all polygon nodes and cure small local self-intersections
+function cureLocalIntersections(start, triangles) {
+    let p = start;
+    do {
+        const a = p.prev,
+            b = p.next.next;
+
+        if (!equals(a, b) && intersects(a, p, p.next, b) && locallyInside(a, b) && locallyInside(b, a)) {
+
+            triangles.push(a.i, p.i, b.i);
+
+            // remove two nodes involved
+            removeNode(p);
+            removeNode(p.next);
+
+            p = start = b;
+        }
+        p = p.next;
+    } while (p !== start);
+
+    return filterPoints(p);
+}
+
+// try splitting polygon into two and triangulate them independently
+function splitEarcut(start, triangles, dim, minX, minY, invSize) {
+    // look for a valid diagonal that divides the polygon into two
+    let a = start;
+    do {
+        let b = a.next.next;
+        while (b !== a.prev) {
+            if (a.i !== b.i && isValidDiagonal(a, b)) {
+                // split the polygon in two by the diagonal
+                let c = splitPolygon(a, b);
+
+                // filter colinear points around the cuts
+                a = filterPoints(a, a.next);
+                c = filterPoints(c, c.next);
+
+                // run earcut on each half
+                earcutLinked(a, triangles, dim, minX, minY, invSize, 0);
+                earcutLinked(c, triangles, dim, minX, minY, invSize, 0);
+                return;
+            }
+            b = b.next;
+        }
+        a = a.next;
+    } while (a !== start);
+}
+
+// link every hole into the outer loop, producing a single-ring polygon without holes
+function eliminateHoles(data, holeIndices, outerNode, dim) {
+    const queue = [];
+
+    for (let i = 0, len = holeIndices.length; i < len; i++) {
+        const start = holeIndices[i] * dim;
+        const end = i < len - 1 ? holeIndices[i + 1] * dim : data.length;
+        const list = linkedList(data, start, end, dim, false);
+        if (list === list.next) list.steiner = true;
+        queue.push(getLeftmost(list));
+    }
+
+    queue.sort(compareXYSlope);
+
+    // process holes from left to right
+    for (let i = 0; i < queue.length; i++) {
+        outerNode = eliminateHole(queue[i], outerNode);
+    }
+
+    return outerNode;
+}
+
+function compareXYSlope(a, b) {
+    let result = a.x - b.x;
+    // when the left-most point of 2 holes meet at a vertex, sort the holes counterclockwise so that when we find
+    // the bridge to the outer shell is always the point that they meet at.
+    if (result === 0) {
+        result = a.y - b.y;
+        if (result === 0) {
+            const aSlope = (a.next.y - a.y) / (a.next.x - a.x);
+            const bSlope = (b.next.y - b.y) / (b.next.x - b.x);
+            result = aSlope - bSlope;
+        }
+    }
+    return result;
+}
+
+// find a bridge between vertices that connects hole with an outer ring and link it
+function eliminateHole(hole, outerNode) {
+    const bridge = findHoleBridge(hole, outerNode);
+    if (!bridge) {
+        return outerNode;
+    }
+
+    const bridgeReverse = splitPolygon(bridge, hole);
+
+    // filter collinear points around the cuts
+    filterPoints(bridgeReverse, bridgeReverse.next);
+    return filterPoints(bridge, bridge.next);
+}
+
+// David Eberly's algorithm for finding a bridge between hole and outer polygon
+function findHoleBridge(hole, outerNode) {
+    let p = outerNode;
+    const hx = hole.x;
+    const hy = hole.y;
+    let qx = -Infinity;
+    let m;
+
+    // find a segment intersected by a ray from the hole's leftmost point to the left;
+    // segment's endpoint with lesser x will be potential connection point
+    // unless they intersect at a vertex, then choose the vertex
+    if (equals(hole, p)) return p;
+    do {
+        if (equals(hole, p.next)) return p.next;
+        else if (hy <= p.y && hy >= p.next.y && p.next.y !== p.y) {
+            const x = p.x + (hy - p.y) * (p.next.x - p.x) / (p.next.y - p.y);
+            if (x <= hx && x > qx) {
+                qx = x;
+                m = p.x < p.next.x ? p : p.next;
+                if (x === hx) return m; // hole touches outer segment; pick leftmost endpoint
+            }
+        }
+        p = p.next;
+    } while (p !== outerNode);
+
+    if (!m) return null;
+
+    // look for points inside the triangle of hole point, segment intersection and endpoint;
+    // if there are no points found, we have a valid connection;
+    // otherwise choose the point of the minimum angle with the ray as connection point
+
+    const stop = m;
+    const mx = m.x;
+    const my = m.y;
+    let tanMin = Infinity;
+
+    p = m;
+
+    do {
+        if (hx >= p.x && p.x >= mx && hx !== p.x &&
+                pointInTriangle(hy < my ? hx : qx, hy, mx, my, hy < my ? qx : hx, hy, p.x, p.y)) {
+
+            const tan = Math.abs(hy - p.y) / (hx - p.x); // tangential
+
+            if (locallyInside(p, hole) &&
+                (tan < tanMin || (tan === tanMin && (p.x > m.x || (p.x === m.x && sectorContainsSector(m, p)))))) {
+                m = p;
+                tanMin = tan;
+            }
+        }
+
+        p = p.next;
+    } while (p !== stop);
+
+    return m;
+}
+
+// whether sector in vertex m contains sector in vertex p in the same coordinates
+function sectorContainsSector(m, p) {
+    return area(m.prev, m, p.prev) < 0 && area(p.next, m, m.next) < 0;
+}
+
+// interlink polygon nodes in z-order
+function indexCurve(start, minX, minY, invSize) {
+    let p = start;
+    do {
+        if (p.z === 0) p.z = zOrder(p.x, p.y, minX, minY, invSize);
+        p.prevZ = p.prev;
+        p.nextZ = p.next;
+        p = p.next;
+    } while (p !== start);
+
+    p.prevZ.nextZ = null;
+    p.prevZ = null;
+
+    sortLinked(p);
+}
+
+// Simon Tatham's linked list merge sort algorithm
+// http://www.chiark.greenend.org.uk/~sgtatham/algorithms/listsort.html
+function sortLinked(list) {
+    let numMerges;
+    let inSize = 1;
+
+    do {
+        let p = list;
+        let e;
+        list = null;
+        let tail = null;
+        numMerges = 0;
+
+        while (p) {
+            numMerges++;
+            let q = p;
+            let pSize = 0;
+            for (let i = 0; i < inSize; i++) {
+                pSize++;
+                q = q.nextZ;
+                if (!q) break;
+            }
+            let qSize = inSize;
+
+            while (pSize > 0 || (qSize > 0 && q)) {
+
+                if (pSize !== 0 && (qSize === 0 || !q || p.z <= q.z)) {
+                    e = p;
+                    p = p.nextZ;
+                    pSize--;
+                } else {
+                    e = q;
+                    q = q.nextZ;
+                    qSize--;
+                }
+
+                if (tail) tail.nextZ = e;
+                else list = e;
+
+                e.prevZ = tail;
+                tail = e;
+            }
+
+            p = q;
+        }
+
+        tail.nextZ = null;
+        inSize *= 2;
+
+    } while (numMerges > 1);
+
+    return list;
+}
+
+// z-order of a point given coords and inverse of the longer side of data bbox
+function zOrder(x, y, minX, minY, invSize) {
+    // coords are transformed into non-negative 15-bit integer range
+    x = (x - minX) * invSize | 0;
+    y = (y - minY) * invSize | 0;
+
+    x = (x | (x << 8)) & 0x00FF00FF;
+    x = (x | (x << 4)) & 0x0F0F0F0F;
+    x = (x | (x << 2)) & 0x33333333;
+    x = (x | (x << 1)) & 0x55555555;
+
+    y = (y | (y << 8)) & 0x00FF00FF;
+    y = (y | (y << 4)) & 0x0F0F0F0F;
+    y = (y | (y << 2)) & 0x33333333;
+    y = (y | (y << 1)) & 0x55555555;
+
+    return x | (y << 1);
+}
+
+// find the leftmost node of a polygon ring
+function getLeftmost(start) {
+    let p = start,
+        leftmost = start;
+    do {
+        if (p.x < leftmost.x || (p.x === leftmost.x && p.y < leftmost.y)) leftmost = p;
+        p = p.next;
+    } while (p !== start);
+
+    return leftmost;
+}
+
+// check if a point lies within a convex triangle
+function pointInTriangle(ax, ay, bx, by, cx, cy, px, py) {
+    return (cx - px) * (ay - py) >= (ax - px) * (cy - py) &&
+           (ax - px) * (by - py) >= (bx - px) * (ay - py) &&
+           (bx - px) * (cy - py) >= (cx - px) * (by - py);
+}
+
+// check if a point lies within a convex triangle but false if its equal to the first point of the triangle
+function pointInTriangleExceptFirst(ax, ay, bx, by, cx, cy, px, py) {
+    return !(ax === px && ay === py) && pointInTriangle(ax, ay, bx, by, cx, cy, px, py);
+}
+
+// check if a diagonal between two polygon nodes is valid (lies in polygon interior)
+function isValidDiagonal(a, b) {
+    return a.next.i !== b.i && a.prev.i !== b.i && !intersectsPolygon(a, b) && // doesn't intersect other edges
+           (locallyInside(a, b) && locallyInside(b, a) && middleInside(a, b) && // locally visible
+            (area(a.prev, a, b.prev) || area(a, b.prev, b)) || // does not create opposite-facing sectors
+            equals(a, b) && area(a.prev, a, a.next) > 0 && area(b.prev, b, b.next) > 0); // special zero-length case
+}
+
+// signed area of a triangle
+function area(p, q, r) {
+    return (q.y - p.y) * (r.x - q.x) - (q.x - p.x) * (r.y - q.y);
+}
+
+// check if two points are equal
+function equals(p1, p2) {
+    return p1.x === p2.x && p1.y === p2.y;
+}
+
+// check if two segments intersect
+function intersects(p1, q1, p2, q2) {
+    const o1 = sign(area(p1, q1, p2));
+    const o2 = sign(area(p1, q1, q2));
+    const o3 = sign(area(p2, q2, p1));
+    const o4 = sign(area(p2, q2, q1));
+
+    if (o1 !== o2 && o3 !== o4) return true; // general case
+
+    if (o1 === 0 && onSegment(p1, p2, q1)) return true; // p1, q1 and p2 are collinear and p2 lies on p1q1
+    if (o2 === 0 && onSegment(p1, q2, q1)) return true; // p1, q1 and q2 are collinear and q2 lies on p1q1
+    if (o3 === 0 && onSegment(p2, p1, q2)) return true; // p2, q2 and p1 are collinear and p1 lies on p2q2
+    if (o4 === 0 && onSegment(p2, q1, q2)) return true; // p2, q2 and q1 are collinear and q1 lies on p2q2
+
+    return false;
+}
+
+// for collinear points p, q, r, check if point q lies on segment pr
+function onSegment(p, q, r) {
+    return q.x <= Math.max(p.x, r.x) && q.x >= Math.min(p.x, r.x) && q.y <= Math.max(p.y, r.y) && q.y >= Math.min(p.y, r.y);
+}
+
+function sign(num) {
+    return num > 0 ? 1 : num < 0 ? -1 : 0;
+}
+
+// check if a polygon diagonal intersects any polygon segments
+function intersectsPolygon(a, b) {
+    let p = a;
+    do {
+        if (p.i !== a.i && p.next.i !== a.i && p.i !== b.i && p.next.i !== b.i &&
+                intersects(p, p.next, a, b)) return true;
+        p = p.next;
+    } while (p !== a);
+
+    return false;
+}
+
+// check if a polygon diagonal is locally inside the polygon
+function locallyInside(a, b) {
+    return area(a.prev, a, a.next) < 0 ?
+        area(a, b, a.next) >= 0 && area(a, a.prev, b) >= 0 :
+        area(a, b, a.prev) < 0 || area(a, a.next, b) < 0;
+}
+
+// check if the middle point of a polygon diagonal is inside the polygon
+function middleInside(a, b) {
+    let p = a;
+    let inside = false;
+    const px = (a.x + b.x) / 2;
+    const py = (a.y + b.y) / 2;
+    do {
+        if (((p.y > py) !== (p.next.y > py)) && p.next.y !== p.y &&
+                (px < (p.next.x - p.x) * (py - p.y) / (p.next.y - p.y) + p.x))
+            inside = !inside;
+        p = p.next;
+    } while (p !== a);
+
+    return inside;
+}
+
+// link two polygon vertices with a bridge; if the vertices belong to the same ring, it splits polygon into two;
+// if one belongs to the outer ring and another to a hole, it merges it into a single ring
+function splitPolygon(a, b) {
+    const a2 = createNode(a.i, a.x, a.y),
+        b2 = createNode(b.i, b.x, b.y),
+        an = a.next,
+        bp = b.prev;
+
+    a.next = b;
+    b.prev = a;
+
+    a2.next = an;
+    an.prev = a2;
+
+    b2.next = a2;
+    a2.prev = b2;
+
+    bp.next = b2;
+    b2.prev = bp;
+
+    return b2;
+}
+
+// create a node and optionally link it with previous one (in a circular doubly linked list)
+function insertNode(i, x, y, last) {
+    const p = createNode(i, x, y);
+
+    if (!last) {
+        p.prev = p;
+        p.next = p;
+
+    } else {
+        p.next = last.next;
+        p.prev = last;
+        last.next.prev = p;
+        last.next = p;
+    }
+    return p;
+}
+
+function removeNode(p) {
+    p.next.prev = p.prev;
+    p.prev.next = p.next;
+
+    if (p.prevZ) p.prevZ.nextZ = p.nextZ;
+    if (p.nextZ) p.nextZ.prevZ = p.prevZ;
+}
+
+function createNode(i, x, y) {
+    return {
+        i, // vertex index in coordinates array
+        x, y, // vertex coordinates
+        prev: null, // previous and next vertex nodes in a polygon ring
+        next: null,
+        z: 0, // z-order curve value
+        prevZ: null, // previous and next nodes in z-order
+        nextZ: null,
+        steiner: false // indicates whether this is a steiner point
+    };
+}
+
+// return a percentage difference between the polygon area and its triangulation area;
+// used to verify correctness of triangulation
+export function deviation(data, holeIndices, dim, triangles) {
+    const hasHoles = holeIndices && holeIndices.length;
+    const outerLen = hasHoles ? holeIndices[0] * dim : data.length;
+
+    let polygonArea = Math.abs(signedArea(data, 0, outerLen, dim));
+    if (hasHoles) {
+        for (let i = 0, len = holeIndices.length; i < len; i++) {
+            const start = holeIndices[i] * dim;
+            const end = i < len - 1 ? holeIndices[i + 1] * dim : data.length;
+            polygonArea -= Math.abs(signedArea(data, start, end, dim));
+        }
+    }
+
+    let trianglesArea = 0;
+    for (let i = 0; i < triangles.length; i += 3) {
+        const a = triangles[i] * dim;
+        const b = triangles[i + 1] * dim;
+        const c = triangles[i + 2] * dim;
+        trianglesArea += Math.abs(
+            (data[a] - data[c]) * (data[b + 1] - data[a + 1]) -
+            (data[a] - data[b]) * (data[c + 1] - data[a + 1]));
+    }
+
+    return polygonArea === 0 && trianglesArea === 0 ? 0 :
+        Math.abs((trianglesArea - polygonArea) / polygonArea);
+}
+
+function signedArea(data, start, end, dim) {
+    let sum = 0;
+    for (let i = start, j = end - dim; i < end; i += dim) {
+        sum += (data[j] - data[i]) * (data[i + 1] + data[j + 1]);
+        j = i;
+    }
+    return sum;
+}
+
+// turn a polygon in a multi-dimensional array form (e.g. as in GeoJSON) into a form Earcut accepts
+export function flatten(data) {
+    const vertices = [];
+    const holes = [];
+    const dimensions = data[0][0].length;
+    let holeIndex = 0;
+    let prevLen = 0;
+
+    for (const ring of data) {
+        for (const p of ring) {
+            for (let d = 0; d < dimensions; d++) vertices.push(p[d]);
+        }
+        if (prevLen) {
+            holeIndex += prevLen;
+            holes.push(holeIndex);
+        }
+        prevLen = ring.length;
+    }
+    return {vertices, holes, dimensions};
+}