✨ Added utils.curveCrossesLine and utils.curveCrossesCurve

src/point.js

@@ -100,6 +100,16 @@ Point.prototype.sitsOn = function(that) {
   else return false;
 };
 
+/** Checks whether this has roughly the same coordinates as that */
+Point.prototype.sitsRoughlyOn = function(that) {
+  if (
+    Math.round(this.x) === Math.round(that.x) &&
+    Math.round(this.y) === Math.round(that.y)
+  )
+    return true;
+  else return false;
+};
+
 /** Shifts this point fraction of the distance towards that point */
 Point.prototype.shiftFractionTowards = function(that, fraction) {
   return this.shiftTowards(that, this.dist(that) * fraction);

src/utils.js

@@ -1,4 +1,5 @@
 import Point from "./point";
+import Bezier from "bezier-js";
 import { round } from "./round";
 
 /** Returns internal hook name for a macro */
@@ -69,3 +70,72 @@ export function units(value, to = "metric") {
   if (to === "imperial") return round(value / 25.4) + '"';
   else return round(value / 10) + "cm";
 }
+
+/** Find where a curve crosses a line */
+export function curveCrossesLine(from, cp1, cp2, to, start, end) {
+  let intersections = [];
+  let bz = new Bezier(
+    { x: from.x, y: from.y },
+    { x: cp1.x, y: cp1.y },
+    { x: cp2.x, y: cp2.y },
+    { x: to.x, y: to.y }
+  );
+  let line = {
+    p1: { x: start.x, y: start.y },
+    p2: { x: end.x, y: end.y }
+  };
+  for (let t of bz.intersects(line)) {
+    let isect = bz.get(t);
+    intersections.push(new Point(isect.x, isect.y));
+  }
+
+  if (intersections.length === 0) return false;
+  else if (intersections.length === 1) return intersections[0];
+  else return intersections;
+}
+
+/** Find where a curve crosses another curve */
+export function curveCrossesCurve(
+  fromA,
+  cp1A,
+  cp2A,
+  toA,
+  fromB,
+  cp1B,
+  cp2B,
+  toB
+) {
+  let precision = 0.005; // See https://github.com/Pomax/bezierjs/issues/99
+  let intersections = [];
+  let curveA = new Bezier(
+    { x: fromA.x, y: fromA.y },
+    { x: cp1A.x, y: cp1A.y },
+    { x: cp2A.x, y: cp2A.y },
+    { x: toA.x, y: toA.y }
+  );
+  let curveB = new Bezier(
+    { x: fromB.x, y: fromB.y },
+    { x: cp1B.x, y: cp1B.y },
+    { x: cp2B.x, y: cp2B.y },
+    { x: toB.x, y: toB.y }
+  );
+
+  for (let tvalues of curveA.intersects(curveB, precision)) {
+    let intersection = curveA.get(tvalues.substr(0, tvalues.indexOf("/")));
+    intersections.push(new Point(intersection.x, intersection.y));
+  }
+
+  if (intersections.length === 0) return false;
+  else if (intersections.length === 1) return intersections.shift();
+  else {
+    let unique = [];
+    for (let i of intersections) {
+      let dupe = false;
+      for (let u of unique) {
+        if (i.sitsRoughlyOn(u)) dupe = true;
+      }
+      if (!dupe) unique.push(i);
+    }
+    return unique;
+  }
+}

tests/utils.test.js

@@ -93,6 +93,86 @@ it("Should detect horizontal lines never pass a give Y-value", () => {
   expect(freesewing.utils.beamCrossesY(a, b, 69)).to.equal(false);
 });
 
+it("Should find no intersections between a curve and a line", () => {
+  let A = new freesewing.Point(10, 10);
+  let Acp = new freesewing.Point(310, 40);
+  let B = new freesewing.Point(110, 70);
+  let Bcp = new freesewing.Point(-210, 40);
+  let E = new freesewing.Point(-20, -20);
+  let D = new freesewing.Point(30, -85);
+
+  let hit = freesewing.utils.curveCrossesLine(A, Acp, Bcp, B, E, D);
+  expect(hit).to.equal(false);
+});
+
+it("Should find 1 intersection between a curve and a line", () => {
+  let A = new freesewing.Point(10, 10);
+  let Acp = new freesewing.Point(310, 40);
+  let B = new freesewing.Point(110, 70);
+  let Bcp = new freesewing.Point(-210, 40);
+  let E = new freesewing.Point(20, 20);
+  let D = new freesewing.Point(30, -85);
+
+  let hit = freesewing.utils.curveCrossesLine(A, Acp, Bcp, B, E, D);
+  expect(hit.x).to.equal(20.85);
+  expect(hit.y).to.equal(11.11);
+});
+
+it("Should find 3 intersections between a curve and a line", () => {
+  let A = new freesewing.Point(10, 10);
+  let Acp = new freesewing.Point(310, 40);
+  let B = new freesewing.Point(110, 70);
+  let Bcp = new freesewing.Point(-210, 40);
+  let E = new freesewing.Point(20, -5);
+  let D = new freesewing.Point(100, 85);
+
+  let hits = freesewing.utils.curveCrossesLine(A, Acp, Bcp, B, E, D);
+  expect(hits.length).to.equal(3);
+});
+
+it("Should find 9 intersections between two curves", () => {
+  let A = new freesewing.Point(10, 10);
+  let Acp = new freesewing.Point(310, 40);
+  let B = new freesewing.Point(110, 70);
+  let Bcp = new freesewing.Point(-210, 40);
+  let C = new freesewing.Point(20, -5);
+  let Ccp = new freesewing.Point(60, 300);
+  let D = new freesewing.Point(100, 85);
+  let Dcp = new freesewing.Point(70, -220);
+
+  let hits = freesewing.utils.curveCrossesCurve(A, Acp, Bcp, B, C, Ccp, Dcp, D);
+  expect(hits.length).to.equal(9);
+});
+
+it("Should find 1 intersection between two curves", () => {
+  let A = new freesewing.Point(10, 10);
+  let Acp = new freesewing.Point(310, 40);
+  let B = new freesewing.Point(110, 70);
+  let Bcp = new freesewing.Point(-210, 40);
+  let C = new freesewing.Point(20, -5);
+  let Ccp = new freesewing.Point(-60, 300);
+  let D = new freesewing.Point(-200, 85);
+  let Dcp = new freesewing.Point(-270, -220);
+
+  let hit = freesewing.utils.curveCrossesCurve(A, Acp, Bcp, B, C, Ccp, Dcp, D);
+  expect(hit.x).to.equal(15.58);
+  expect(hit.y).to.equal(10.56);
+});
+
+it("Should find no intersection between two curves", () => {
+  let A = new freesewing.Point(10, 10);
+  let Acp = new freesewing.Point(310, 40);
+  let B = new freesewing.Point(110, 70);
+  let Bcp = new freesewing.Point(-210, 40);
+  let C = new freesewing.Point(20, -5);
+  let Ccp = new freesewing.Point(-60, -300);
+  let D = new freesewing.Point(-200, 85);
+  let Dcp = new freesewing.Point(-270, -220);
+
+  let hit = freesewing.utils.curveCrossesCurve(A, Acp, Bcp, B, C, Ccp, Dcp, D);
+  expect(hit).to.equal(false);
+});
+
 it("Should correctly format units", () => {
   expect(freesewing.utils.units(123.456)).to.equal("12.35cm");
   expect(freesewing.utils.units(123.456, "imperial")).to.equal('4.86"');