@math.gl/polygon/dist/cut-by-grid.js

Polygon/polyline processing utilities

// math.gl
// SPDX-License-Identifier: MIT
// Copyright (c) vis.gl contributors
/* eslint-disable max-statements, max-depth, complexity, no-unused-expressions */
import { bitCode, intersect } from "./lineclip.js";
import { getPointAtIndex, copy, push } from "./utils.js";
export function cutPolylineByGrid(positions, options) {
    const { size = 2, broken = false, gridResolution = 10, gridOffset = [0, 0], startIndex = 0, endIndex = positions.length } = options || {};
    const numPoints = (endIndex - startIndex) / size;
    let part = [];
    const result = [part];
    const a = getPointAtIndex(positions, 0, size, startIndex);
    let b;
    let codeB;
    const cell = getGridCell(a, gridResolution, gridOffset, []);
    const scratchPoint = [];
    push(part, a);
    for (let i = 1; i < numPoints; i++) {
        b = getPointAtIndex(positions, i, size, startIndex, b);
        codeB = bitCode(b, cell);
        while (codeB) {
            // find the intersection with the current cell
            intersect(a, b, codeB, cell, scratchPoint);
            const codeAlt = bitCode(scratchPoint, cell);
            if (codeAlt) {
                intersect(a, scratchPoint, codeAlt, cell, scratchPoint);
                codeB = codeAlt;
            }
            push(part, scratchPoint);
            // move to the next cell
            copy(a, scratchPoint);
            moveToNeighborCell(cell, gridResolution, codeB);
            if (broken && part.length > size) {
                part = [];
                result.push(part);
                push(part, a);
            }
            codeB = bitCode(b, cell);
        }
        push(part, b);
        copy(a, b);
    }
    return broken ? result : result[0];
}
const TYPE_INSIDE = 0;
const TYPE_BORDER = 1;
/**
 * Cuts a polygon by a pre-defined grid
 */
export function cutPolygonByGrid(positions, holeIndices = null, options) {
    if (!positions.length) {
        // input is empty
        return [];
    }
    const { size = 2, gridResolution = 10, gridOffset = [0, 0], edgeTypes = false } = options || {};
    const result = [];
    const queue = [
        {
            pos: positions,
            types: edgeTypes ? new Array(positions.length / size).fill(TYPE_BORDER) : null,
            holes: holeIndices || []
        }
    ];
    const bbox = [[], []];
    // @ts-ignore
    let cell = [];
    // Recursively bisect polygon until every part fit in a single grid cell
    while (queue.length) {
        const { pos, types, holes } = queue.shift();
        // Get the bounding box of the outer polygon
        getBoundingBox(pos, size, holes[0] || pos.length, bbox);
        cell = getGridCell(bbox[0], gridResolution, gridOffset, cell);
        const code = bitCode(bbox[1], cell);
        if (code) {
            // Split the outer ring at the boundary
            let parts = bisectPolygon(pos, types, size, 0, holes[0] || pos.length, cell, code);
            const polygonLow = { pos: parts[0].pos, types: parts[0].types, holes: [] };
            const polygonHigh = { pos: parts[1].pos, types: parts[1].types, holes: [] };
            queue.push(polygonLow, polygonHigh);
            // Split each hole at the boundary
            for (let i = 0; i < holes.length; i++) {
                parts = bisectPolygon(pos, types, size, holes[i], holes[i + 1] || pos.length, cell, code);
                if (parts[0]) {
                    polygonLow.holes.push(polygonLow.pos.length);
                    polygonLow.pos = concatInPlace(polygonLow.pos, parts[0].pos);
                    if (edgeTypes) {
                        polygonLow.types = concatInPlace(polygonLow.types, parts[0].types);
                    }
                }
                if (parts[1]) {
                    polygonHigh.holes.push(polygonHigh.pos.length);
                    polygonHigh.pos = concatInPlace(polygonHigh.pos, parts[1].pos);
                    if (edgeTypes) {
                        polygonHigh.types = concatInPlace(polygonHigh.types, parts[1].types);
                    }
                }
            }
        }
        else {
            // Polygon fits in a single cell, no more processing required
            const polygon = { positions: pos };
            if (edgeTypes) {
                polygon.edgeTypes = types;
            }
            if (holes.length) {
                polygon.holeIndices = holes;
            }
            result.push(polygon);
        }
    }
    return result;
}
// edgeTypes:
// TYPE_BORDER - edge from the original polygon
// TYPE_INSIDE - inside the original polygon
// eslint-disable-next-line max-params
function bisectPolygon(positions, edgeTypes, size, startIndex, endIndex, bbox, edge) {
    const numPoints = (endIndex - startIndex) / size;
    const resultLow = [];
    const resultHigh = [];
    const typesLow = [];
    const typesHigh = [];
    const scratchPoint = [];
    let p;
    let side;
    let type;
    const prev = getPointAtIndex(positions, numPoints - 1, size, startIndex);
    let prevSide = Math.sign(edge & 8 ? prev[1] - bbox[3] : prev[0] - bbox[2]);
    let prevType = edgeTypes && edgeTypes[numPoints - 1];
    let lowPointCount = 0;
    let highPointCount = 0;
    for (let i = 0; i < numPoints; i++) {
        p = getPointAtIndex(positions, i, size, startIndex, p);
        side = Math.sign(edge & 8 ? p[1] - bbox[3] : p[0] - bbox[2]);
        type = edgeTypes && edgeTypes[startIndex / size + i];
        // if segment goes through the boundary, add an intersection
        if (side && prevSide && prevSide !== side) {
            intersect(prev, p, edge, bbox, scratchPoint);
            push(resultLow, scratchPoint) && typesLow.push(prevType);
            push(resultHigh, scratchPoint) && typesHigh.push(prevType);
        }
        if (side <= 0) {
            push(resultLow, p) && typesLow.push(type);
            lowPointCount -= side;
        }
        else if (typesLow.length) {
            typesLow[typesLow.length - 1] = TYPE_INSIDE;
        }
        if (side >= 0) {
            push(resultHigh, p) && typesHigh.push(type);
            highPointCount += side;
        }
        else if (typesHigh.length) {
            typesHigh[typesHigh.length - 1] = TYPE_INSIDE;
        }
        copy(prev, p);
        prevSide = side;
        prevType = type;
    }
    return [
        lowPointCount ? { pos: resultLow, types: edgeTypes && typesLow } : null,
        highPointCount ? { pos: resultHigh, types: edgeTypes && typesHigh } : null
    ];
}
function getGridCell(p, gridResolution, gridOffset, out) {
    const left = Math.floor((p[0] - gridOffset[0]) / gridResolution) * gridResolution + gridOffset[0];
    const bottom = Math.floor((p[1] - gridOffset[1]) / gridResolution) * gridResolution + gridOffset[1];
    out[0] = left;
    out[1] = bottom;
    out[2] = left + gridResolution;
    out[3] = bottom + gridResolution;
    return out;
}
function moveToNeighborCell(cell, gridResolution, edge) {
    if (edge & 8) {
        // top
        cell[1] += gridResolution;
        cell[3] += gridResolution;
    }
    else if (edge & 4) {
        // bottom
        cell[1] -= gridResolution;
        cell[3] -= gridResolution;
    }
    else if (edge & 2) {
        // right
        cell[0] += gridResolution;
        cell[2] += gridResolution;
    }
    else if (edge & 1) {
        // left
        cell[0] -= gridResolution;
        cell[2] -= gridResolution;
    }
}
function getBoundingBox(positions, size, endIndex, out) {
    let minX = Infinity;
    let maxX = -Infinity;
    let minY = Infinity;
    let maxY = -Infinity;
    for (let i = 0; i < endIndex; i += size) {
        const x = positions[i];
        const y = positions[i + 1];
        minX = x < minX ? x : minX;
        maxX = x > maxX ? x : maxX;
        minY = y < minY ? y : minY;
        maxY = y > maxY ? y : maxY;
    }
    out[0][0] = minX;
    out[0][1] = minY;
    out[1][0] = maxX;
    out[1][1] = maxY;
    return out;
}
function concatInPlace(arr1, arr2) {
    for (let i = 0; i < arr2.length; i++) {
        arr1.push(arr2[i]);
    }
    return arr1;
}
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