sweepline-intersections/dist/SweeplineIntersectionsClass.esm.js

A module to check if a polygon self-intersects using a sweepline algorithm

class TinyQueue {
    constructor(data = [], compare = defaultCompare) {
        this.data = data;
        this.length = this.data.length;
        this.compare = compare;

        if (this.length > 0) {
            for (let i = (this.length >> 1) - 1; i >= 0; i--) this._down(i);
        }
    }

    push(item) {
        this.data.push(item);
        this.length++;
        this._up(this.length - 1);
    }

    pop() {
        if (this.length === 0) return undefined;

        const top = this.data[0];
        const bottom = this.data.pop();
        this.length--;

        if (this.length > 0) {
            this.data[0] = bottom;
            this._down(0);
        }

        return top;
    }

    peek() {
        return this.data[0];
    }

    _up(pos) {
        const {data, compare} = this;
        const item = data[pos];

        while (pos > 0) {
            const parent = (pos - 1) >> 1;
            const current = data[parent];
            if (compare(item, current) >= 0) break;
            data[pos] = current;
            pos = parent;
        }

        data[pos] = item;
    }

    _down(pos) {
        const {data, compare} = this;
        const halfLength = this.length >> 1;
        const item = data[pos];

        while (pos < halfLength) {
            let left = (pos << 1) + 1;
            let best = data[left];
            const right = left + 1;

            if (right < this.length && compare(data[right], best) < 0) {
                left = right;
                best = data[right];
            }
            if (compare(best, item) >= 0) break;

            data[pos] = best;
            pos = left;
        }

        data[pos] = item;
    }
}

function defaultCompare(a, b) {
    return a < b ? -1 : a > b ? 1 : 0;
}

function checkWhichEventIsLeft (e1, e2) {
    if (e1.p.x > e2.p.x) return 1
    if (e1.p.x < e2.p.x) return -1

    if (e1.p.x === e2.p.x && (e1.featureId !== e2.featureId || e1.ringId !== e2.ringId)) {
        if (e1.isLeftEndpoint && !e2.isLeftEndpoint) return -1
    }

    if (e1.p.y !== e2.p.y) return e1.p.y > e2.p.y ? 1 : -1
    return 1
}

function checkWhichSegmentHasRightEndpointFirst (seg1, seg2) {
    if (seg1.rightSweepEvent.p.x > seg2.rightSweepEvent.p.x) return 1
    if (seg1.rightSweepEvent.p.x < seg2.rightSweepEvent.p.x) return -1

    if (seg1.rightSweepEvent.p.y !== seg2.rightSweepEvent.p.y) {
        return seg1.rightSweepEvent.p.y < seg2.rightSweepEvent.p.y ? 1 : -1
    }
    return 1
}

class Event {

    constructor (p, featureId, ringId, eventId) {
        this.p = {
            x: p[0],
            y: p[1]
        };
        this.featureId = featureId;
        this.ringId = ringId;
        this.eventId = eventId;

        this.otherEvent = null;
        this.isLeftEndpoint = null;
    }

    isSamePoint (eventToCheck) {
        return this.p.x === eventToCheck.p.x && this.p.y === eventToCheck.p.y
    }

    asNewXY () {
        return [this.p.x, this.p.y]
    }
}

function fillEventQueue (geojson, eventQueue) {
    if (geojson.type === 'FeatureCollection') {
        const features = geojson.features;
        for (let i = 0; i < features.length; i++) {
            processFeature(features[i], eventQueue);
        }
    } else {
        processFeature(geojson, eventQueue);
    }
}

let featureId = 0;
let ringId = 0;
let eventId = 0;
function processFeature (featureOrGeometry, eventQueue) {
    const geom = featureOrGeometry.type === 'Feature' ? featureOrGeometry.geometry : featureOrGeometry;
    let coords = geom.coordinates;
    // standardise the input
    if (geom.type === 'Polygon' || geom.type === 'MultiLineString') coords = [coords];
    if (geom.type === 'LineString') coords = [[coords]];

    for (let i = 0; i < coords.length; i++) {
        for (let ii = 0; ii < coords[i].length; ii++) {
            let currentP = coords[i][ii][0];
            let nextP = null;
            ringId = ringId + 1;
            for (let iii = 0; iii < coords[i][ii].length - 1; iii++) {
                nextP = coords[i][ii][iii + 1];

                const e1 = new Event(currentP, featureId, ringId, eventId);
                const e2 = new Event(nextP, featureId, ringId, eventId + 1);

                e1.otherEvent = e2;
                e2.otherEvent = e1;

                if (checkWhichEventIsLeft(e1, e2) > 0) {
                    e2.isLeftEndpoint = true;
                    e1.isLeftEndpoint = false;
                } else {
                    e1.isLeftEndpoint = true;
                    e2.isLeftEndpoint = false;
                }
                eventQueue.push(e1);
                eventQueue.push(e2);

                currentP = nextP;
                eventId = eventId + 1;
            }
        }
    }
    featureId = featureId + 1;
}

class Segment {

    constructor (event) {
        this.leftSweepEvent = event;
        this.rightSweepEvent = event.otherEvent;
    }
}

const epsilon = 1.1102230246251565e-16;
const splitter = 134217729;
const resulterrbound = (3 + 8 * epsilon) * epsilon;

// fast_expansion_sum_zeroelim routine from oritinal code
function sum(elen, e, flen, f, h) {
    let Q, Qnew, hh, bvirt;
    let enow = e[0];
    let fnow = f[0];
    let eindex = 0;
    let findex = 0;
    if ((fnow > enow) === (fnow > -enow)) {
        Q = enow;
        enow = e[++eindex];
    } else {
        Q = fnow;
        fnow = f[++findex];
    }
    let hindex = 0;
    if (eindex < elen && findex < flen) {
        if ((fnow > enow) === (fnow > -enow)) {
            Qnew = enow + Q;
            hh = Q - (Qnew - enow);
            enow = e[++eindex];
        } else {
            Qnew = fnow + Q;
            hh = Q - (Qnew - fnow);
            fnow = f[++findex];
        }
        Q = Qnew;
        if (hh !== 0) {
            h[hindex++] = hh;
        }
        while (eindex < elen && findex < flen) {
            if ((fnow > enow) === (fnow > -enow)) {
                Qnew = Q + enow;
                bvirt = Qnew - Q;
                hh = Q - (Qnew - bvirt) + (enow - bvirt);
                enow = e[++eindex];
            } else {
                Qnew = Q + fnow;
                bvirt = Qnew - Q;
                hh = Q - (Qnew - bvirt) + (fnow - bvirt);
                fnow = f[++findex];
            }
            Q = Qnew;
            if (hh !== 0) {
                h[hindex++] = hh;
            }
        }
    }
    while (eindex < elen) {
        Qnew = Q + enow;
        bvirt = Qnew - Q;
        hh = Q - (Qnew - bvirt) + (enow - bvirt);
        enow = e[++eindex];
        Q = Qnew;
        if (hh !== 0) {
            h[hindex++] = hh;
        }
    }
    while (findex < flen) {
        Qnew = Q + fnow;
        bvirt = Qnew - Q;
        hh = Q - (Qnew - bvirt) + (fnow - bvirt);
        fnow = f[++findex];
        Q = Qnew;
        if (hh !== 0) {
            h[hindex++] = hh;
        }
    }
    if (Q !== 0 || hindex === 0) {
        h[hindex++] = Q;
    }
    return hindex;
}

function estimate(elen, e) {
    let Q = e[0];
    for (let i = 1; i < elen; i++) Q += e[i];
    return Q;
}

function vec(n) {
    return new Float64Array(n);
}

const ccwerrboundA = (3 + 16 * epsilon) * epsilon;
const ccwerrboundB = (2 + 12 * epsilon) * epsilon;
const ccwerrboundC = (9 + 64 * epsilon) * epsilon * epsilon;

const B = vec(4);
const C1 = vec(8);
const C2 = vec(12);
const D = vec(16);
const u = vec(4);

function orient2dadapt(ax, ay, bx, by, cx, cy, detsum) {
    let acxtail, acytail, bcxtail, bcytail;
    let bvirt, c, ahi, alo, bhi, blo, _i, _j, _0, s1, s0, t1, t0, u3;

    const acx = ax - cx;
    const bcx = bx - cx;
    const acy = ay - cy;
    const bcy = by - cy;

    s1 = acx * bcy;
    c = splitter * acx;
    ahi = c - (c - acx);
    alo = acx - ahi;
    c = splitter * bcy;
    bhi = c - (c - bcy);
    blo = bcy - bhi;
    s0 = alo * blo - (s1 - ahi * bhi - alo * bhi - ahi * blo);
    t1 = acy * bcx;
    c = splitter * acy;
    ahi = c - (c - acy);
    alo = acy - ahi;
    c = splitter * bcx;
    bhi = c - (c - bcx);
    blo = bcx - bhi;
    t0 = alo * blo - (t1 - ahi * bhi - alo * bhi - ahi * blo);
    _i = s0 - t0;
    bvirt = s0 - _i;
    B[0] = s0 - (_i + bvirt) + (bvirt - t0);
    _j = s1 + _i;
    bvirt = _j - s1;
    _0 = s1 - (_j - bvirt) + (_i - bvirt);
    _i = _0 - t1;
    bvirt = _0 - _i;
    B[1] = _0 - (_i + bvirt) + (bvirt - t1);
    u3 = _j + _i;
    bvirt = u3 - _j;
    B[2] = _j - (u3 - bvirt) + (_i - bvirt);
    B[3] = u3;

    let det = estimate(4, B);
    let errbound = ccwerrboundB * detsum;
    if (det >= errbound || -det >= errbound) {
        return det;
    }

    bvirt = ax - acx;
    acxtail = ax - (acx + bvirt) + (bvirt - cx);
    bvirt = bx - bcx;
    bcxtail = bx - (bcx + bvirt) + (bvirt - cx);
    bvirt = ay - acy;
    acytail = ay - (acy + bvirt) + (bvirt - cy);
    bvirt = by - bcy;
    bcytail = by - (bcy + bvirt) + (bvirt - cy);

    if (acxtail === 0 && acytail === 0 && bcxtail === 0 && bcytail === 0) {
        return det;
    }

    errbound = ccwerrboundC * detsum + resulterrbound * Math.abs(det);
    det += (acx * bcytail + bcy * acxtail) - (acy * bcxtail + bcx * acytail);
    if (det >= errbound || -det >= errbound) return det;

    s1 = acxtail * bcy;
    c = splitter * acxtail;
    ahi = c - (c - acxtail);
    alo = acxtail - ahi;
    c = splitter * bcy;
    bhi = c - (c - bcy);
    blo = bcy - bhi;
    s0 = alo * blo - (s1 - ahi * bhi - alo * bhi - ahi * blo);
    t1 = acytail * bcx;
    c = splitter * acytail;
    ahi = c - (c - acytail);
    alo = acytail - ahi;
    c = splitter * bcx;
    bhi = c - (c - bcx);
    blo = bcx - bhi;
    t0 = alo * blo - (t1 - ahi * bhi - alo * bhi - ahi * blo);
    _i = s0 - t0;
    bvirt = s0 - _i;
    u[0] = s0 - (_i + bvirt) + (bvirt - t0);
    _j = s1 + _i;
    bvirt = _j - s1;
    _0 = s1 - (_j - bvirt) + (_i - bvirt);
    _i = _0 - t1;
    bvirt = _0 - _i;
    u[1] = _0 - (_i + bvirt) + (bvirt - t1);
    u3 = _j + _i;
    bvirt = u3 - _j;
    u[2] = _j - (u3 - bvirt) + (_i - bvirt);
    u[3] = u3;
    const C1len = sum(4, B, 4, u, C1);

    s1 = acx * bcytail;
    c = splitter * acx;
    ahi = c - (c - acx);
    alo = acx - ahi;
    c = splitter * bcytail;
    bhi = c - (c - bcytail);
    blo = bcytail - bhi;
    s0 = alo * blo - (s1 - ahi * bhi - alo * bhi - ahi * blo);
    t1 = acy * bcxtail;
    c = splitter * acy;
    ahi = c - (c - acy);
    alo = acy - ahi;
    c = splitter * bcxtail;
    bhi = c - (c - bcxtail);
    blo = bcxtail - bhi;
    t0 = alo * blo - (t1 - ahi * bhi - alo * bhi - ahi * blo);
    _i = s0 - t0;
    bvirt = s0 - _i;
    u[0] = s0 - (_i + bvirt) + (bvirt - t0);
    _j = s1 + _i;
    bvirt = _j - s1;
    _0 = s1 - (_j - bvirt) + (_i - bvirt);
    _i = _0 - t1;
    bvirt = _0 - _i;
    u[1] = _0 - (_i + bvirt) + (bvirt - t1);
    u3 = _j + _i;
    bvirt = u3 - _j;
    u[2] = _j - (u3 - bvirt) + (_i - bvirt);
    u[3] = u3;
    const C2len = sum(C1len, C1, 4, u, C2);

    s1 = acxtail * bcytail;
    c = splitter * acxtail;
    ahi = c - (c - acxtail);
    alo = acxtail - ahi;
    c = splitter * bcytail;
    bhi = c - (c - bcytail);
    blo = bcytail - bhi;
    s0 = alo * blo - (s1 - ahi * bhi - alo * bhi - ahi * blo);
    t1 = acytail * bcxtail;
    c = splitter * acytail;
    ahi = c - (c - acytail);
    alo = acytail - ahi;
    c = splitter * bcxtail;
    bhi = c - (c - bcxtail);
    blo = bcxtail - bhi;
    t0 = alo * blo - (t1 - ahi * bhi - alo * bhi - ahi * blo);
    _i = s0 - t0;
    bvirt = s0 - _i;
    u[0] = s0 - (_i + bvirt) + (bvirt - t0);
    _j = s1 + _i;
    bvirt = _j - s1;
    _0 = s1 - (_j - bvirt) + (_i - bvirt);
    _i = _0 - t1;
    bvirt = _0 - _i;
    u[1] = _0 - (_i + bvirt) + (bvirt - t1);
    u3 = _j + _i;
    bvirt = u3 - _j;
    u[2] = _j - (u3 - bvirt) + (_i - bvirt);
    u[3] = u3;
    const Dlen = sum(C2len, C2, 4, u, D);

    return D[Dlen - 1];
}

function orient2d(ax, ay, bx, by, cx, cy) {
    const detleft = (ay - cy) * (bx - cx);
    const detright = (ax - cx) * (by - cy);
    const det = detleft - detright;

    if (detleft === 0 || detright === 0 || (detleft > 0) !== (detright > 0)) return det;

    const detsum = Math.abs(detleft + detright);
    if (Math.abs(det) >= ccwerrboundA * detsum) return det;

    return -orient2dadapt(ax, ay, bx, by, cx, cy, detsum);
}

function testSegmentIntersect (seg1, seg2) {
    if (seg1 === null || seg2 === null) return false

    const x1 = seg1.leftSweepEvent.p.x;
    const y1 = seg1.leftSweepEvent.p.y;
    const x2 = seg1.rightSweepEvent.p.x;
    const y2 = seg1.rightSweepEvent.p.y;
    const x3 = seg2.leftSweepEvent.p.x;
    const y3 = seg2.leftSweepEvent.p.y;
    const x4 = seg2.rightSweepEvent.p.x;
    const y4 = seg2.rightSweepEvent.p.y;

    const score1 = orient2d(x1, y1, x2, y2, x3, y3);
    const score2 = orient2d(x1, y1, x2, y2, x4, y4);

    if (score1 > 0 && score2 > 0) return false
    else if (score1 < 0 && score2 < 0) return false

    if (seg1.leftSweepEvent.ringId === seg2.leftSweepEvent.ringId) {
        if (
            seg1.rightSweepEvent.isSamePoint(seg2.leftSweepEvent) ||
            seg1.rightSweepEvent.isSamePoint(seg2.rightSweepEvent) ||
            seg1.leftSweepEvent.isSamePoint(seg2.leftSweepEvent) ||
            seg1.leftSweepEvent.isSamePoint(seg2.rightSweepEvent)
        ) return false
    } else {
        if (seg1.rightSweepEvent.isSamePoint(seg2.leftSweepEvent)) return seg2.leftSweepEvent.asNewXY()
        if (seg1.rightSweepEvent.isSamePoint(seg2.rightSweepEvent)) return seg2.rightSweepEvent.asNewXY()
        if (seg1.leftSweepEvent.isSamePoint(seg2.leftSweepEvent)) return seg2.leftSweepEvent.asNewXY()
        if (seg1.leftSweepEvent.isSamePoint(seg2.rightSweepEvent)) return seg2.rightSweepEvent.asNewXY()
    }


    const denom = ((y4 - y3) * (x2 - x1)) - ((x4 - x3) * (y2 - y1));
    const numeA = ((x4 - x3) * (y1 - y3)) - ((y4 - y3) * (x1 - x3));
    const numeB = ((x2 - x1) * (y1 - y3)) - ((y2 - y1) * (x1 - x3));

    if (denom === 0) {
        if (numeA === 0 && numeB === 0) return false
        return false
    }

    const uA = numeA / denom;
    const uB = numeB / denom;

    if (uA >= 0 && uA <= 1 && uB >= 0 && uB <= 1) {
        const x = x1 + (uA * (x2 - x1));
        const y = y1 + (uA * (y2 - y1));
        return [x, y]
    }
    return false
}

// import {debugEventAndSegments, debugRemovingSegment} from './debug'

function runCheck (eventQueue, ignoreSelfIntersections) {
    ignoreSelfIntersections = ignoreSelfIntersections ? ignoreSelfIntersections : false;

    const intersectionPoints = [];
    const outQueue = new TinyQueue([], checkWhichSegmentHasRightEndpointFirst);

    while (eventQueue.length) {
        const event = eventQueue.pop();
        if (event.isLeftEndpoint) {
            // debugEventAndSegments(event.p, outQueue.data)
            const segment = new Segment(event);
            for (let i = 0; i < outQueue.data.length; i++) {
                const otherSeg = outQueue.data[i];
                if (ignoreSelfIntersections) {
                    if (otherSeg.leftSweepEvent.featureId === event.featureId) continue
                }
                const intersection = testSegmentIntersect(segment, otherSeg);
                if (intersection !== false) intersectionPoints.push(intersection);
            }
            outQueue.push(segment);
        } else if (event.isLeftEndpoint === false) {
            outQueue.pop();
            // const seg = outQueue.pop()
            // debugRemovingSegment(event.p, seg)
        }
    }
    return intersectionPoints
}

class SweeplineIntersections {

    constructor () {
        this._eventQueue = new TinyQueue([], checkWhichEventIsLeft);
    }

    addData (geojson, alternateEventQueue) {
        if (alternateEventQueue !== undefined) {
            const newQueue = new TinyQueue([], checkWhichEventIsLeft);
            for (let i = 0; i < alternateEventQueue.length; i++) {
                newQueue.push(alternateEventQueue.data[i]);
            }
            this._eventQueue = newQueue;
        }
        fillEventQueue(geojson, this._eventQueue);
    }

    cloneEventQueue () {
        const newQueue = new TinyQueue([], checkWhichEventIsLeft);
        for (let i = 0; i < this._eventQueue.length; i++) {
            newQueue.push(this._eventQueue.data[i]);
        }
        return newQueue
    }

    getIntersections (ignoreSelfIntersections) {
        return runCheck(this._eventQueue, ignoreSelfIntersections)
    }
}

export { SweeplineIntersections as default };