@flatten-js/polygon-offset
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Polygon equidistant offset
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<h1 class="page-title">polygonOffset.js</h1>
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<pre class="prettyprint source linenums"><code>
/**
* Created by Alex Bol on 12/02/2018.
*/
"use strict";
import {Point, Segment, Vector, Line, Box, Arc, Polygon, Face} from "@flatten-js/core";
import {CW, CCW, INSIDE, OUTSIDE, ORIENTATION} from "@flatten-js/core";
import {point, segment, vector} from "@flatten-js/core";
import {unify,subtract} from "@flatten-js/boolean-op";
import {BOOLEAN_UNION} from "@flatten-js/boolean-op";
import {addToIntPoints, getSortedArray, splitByIntersections} from "@flatten-js/boolean-op";
import {removeNotRelevantChains, removeOldFaces, restoreFaces} from "@flatten-js/boolean-op";
import {arcSE, arcStartSweep, arcEndSweep} from "./createArcs";
/**
* Offset polygon by given value
* @param {Polygon} polygon - input polygon
* @param {number} value - offset value, may be positive or negative
* @returns {Polygon} offsetPolygon
*/
/**
*
* @param polygon
* @param value
*
*/
export function offset(polygon, value) {
let w = value;
let edges = [...polygon.edges];
let offsetPolygon = polygon.clone();
let offsetEdge;
if (w != 0) {
for (let edge of edges) {
if (edge.isSegment()) {
offsetEdge = offsetSegment(edge.shape, w);
}
else {
offsetEdge = offsetArc(edge.shape, w);
}
if (w > 0) {
offsetPolygon = unify(offsetPolygon, offsetEdge);
}
else {
offsetPolygon = subtract(offsetPolygon, offsetEdge);
}
}
}
return offsetPolygon;
}
function offsetArc(arc, value) {
let edges = [];
let w = Math.abs(value);
// Define outline polygon
let polygon = new Polygon();
let arc_cap1,arc_cap2;
let arc_outer = arc.clone();
arc_outer.r = arc.r + w;
arc_cap1 = arcStartSweep(arc.end, arc_outer.end, Math.PI, arc.counterClockwise);
arc_cap2 = arcEndSweep(arc.start, arc_outer.start, Math.PI, arc.counterClockwise);
let arc_inner = undefined;
if (arc.r > w) {
arc_inner = new Arc(arc.pc, arc.r - w, arc.endAngle, arc.startAngle,
arc.counterClockwise === CW ? CCW : CW);
}
else {
// arc_inner = new Arc(arc.pc, w - arc.r, arc.startAngle, arc.endAngle, arc.counterClockwise);
arc_inner = new Segment(arc_cap1.end, arc_cap2.start);
}
polygon.addFace([arc_outer, arc_cap1, arc_inner, arc_cap2]);
[...polygon.faces][0].setArcLength();
// Create intersection points
let ips = Face.getSelfIntersections([...polygon.faces][0], polygon.edges, false);
// TODO: getSelfIntersections returns points with correspondent edges - avoid duplication
ips = ips.slice(0,ips.length/2); // for now slice array to avoid duplication in points
let int_points = [];
let edge_cap1;
let edge_cap2;
edge_cap1 = [...polygon.edges][1];
edge_cap2 = [...polygon.edges][3];
for (let pt of ips) {
addToIntPoints(edge_cap1, pt, int_points);
addToIntPoints(edge_cap2, pt, int_points);
}
// Sort intersection points and insert them as new vertices
let int_points_sorted = getSortedArray(int_points);
splitByIntersections(polygon, int_points_sorted);
// Set BV flags
let bv = OUTSIDE;
for (let int_point of int_points_sorted) {
int_point.edge_before.bv = bv;
int_point.edge_after.bv = (bv == OUTSIDE ? INSIDE : OUTSIDE);
bv = int_point.edge_after.bv; // invert flag on each iteration
}
// Remove inner "chains"
let op = BOOLEAN_UNION;
removeNotRelevantChains(polygon, op, int_points_sorted, true);
// return int_points_sorted;
// Swap links
let num = int_points.length;
if (num > 0) {
let edge_before;
let edge_after;
// 0 => 3
edge_before = int_points_sorted[0].edge_before;
edge_after = int_points_sorted[num-1].edge_after;
edge_before.next = edge_after;
edge_after.prev = edge_before;
// Fill in missed links in intersection points
int_points_sorted[0].edge_after = int_points_sorted[num-1].edge_after;
int_points_sorted[num-1].edge_before = int_points_sorted[0].edge_before;
if (num == 4) {
// 2 => 1
edge_before = int_points_sorted[2].edge_before;
edge_after = int_points_sorted[1].edge_after;
edge_before.next = edge_after;
edge_after.prev = edge_before;
// Fill in missed links in intersection points
int_points_sorted[2].edge_after = int_points_sorted[1].edge_after;
int_points_sorted[1].edge_before = int_points_sorted[2].edge_before;
}
// remove old faces
removeOldFaces(polygon, int_points);
// restore faces
restoreFaces(polygon, int_points, int_points);
}
let face0 = [...polygon.faces][0];
if (face0.orientation() === ORIENTATION.CCW) {
polygon.reverse();
}
return polygon;
}
function offsetSegment(seg, value) {
let w = Math.abs(value);
let polygon = new Polygon();
let v_seg = vector(seg.end.x-seg.start.x, seg.end.y-seg.start.y);
let v_seg_unit = v_seg.normalize();
let v_left = v_seg_unit.rotate90CCW().multiply(w);
let v_right = v_seg_unit.rotate90CW().multiply(w);
let seg_left = seg.translate(v_left);
let seg_right = seg.translate(v_right).reverse();
let cap1 = arcSE(seg.end, seg_left.end, seg_right.start, CW);
let cap2 = arcSE(seg.start, seg_right.end, seg_left.start, CW);
polygon.addFace([seg_left, cap1, seg_right, cap2]);
return polygon;
}
</code></pre>
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