fix(core): Edge case in utils.beamsIntersect()

See #1206 for details

Closes #1206
Closes #1211

config/changelog.yaml

@@ -1,3 +1,11 @@
+unreleased:
+  date: 2021-08-01
+
+  Fixed:
+    core:
+      - Fixed edge case in utils.beamsIntersect() when line is almost vertical
+        See [#1206](https://github.com/freesewing/freesewing/issues/1206)
+
 2.17.0:
   date: 2021-07-01
 

packages/core/src/utils.js

@@ -22,12 +22,15 @@ export function macroName(name) {
 export function beamsIntersect(a1, a2, b1, b2) {
   let slopeA = a1.slope(a2)
   let slopeB = b1.slope(b2)
+  console.log({a1, a2, slopeA})
   if (slopeA === slopeB) return false // Parallel lines
 
-  if (a1.x === a2.x) return new Point(a1.x, slopeB * a1.x + (b1.y - slopeB * b1.x))
+  // Check for vertical line A
-  // Vertical line A
+  if (Math.round(a1.x*10000) === Math.round(a2.x*10000))
-  else if (b1.x === b2.x) return new Point(b1.x, slopeA * b1.x + (a1.y - slopeA * a1.x))
+    return new Point(a1.x, slopeB * a1.x + (b1.y - slopeB * b1.x))
-  // Vertical line B
+  // Check for vertical line B
+  else if (Math.round(b1.x*10000) === Math.round(b2.x*10000))
+    return new Point(b1.x, slopeA * b1.x + (a1.y - slopeA * a1.x))
   else {
     // Swap points if line A or B goes from right to left
     if (a1.x > a2.x) a1 = a2.copy()

packages/core/tests/utils.test.js

@@ -490,3 +490,12 @@ it("Should find where a curve intersects a given Y-value", () => {
   expect(round(i.x)).to.equal(39.49);
   expect(round(i.y)).to.equal(30);
 });
+
+// Recreate issue #1206
+it("Should find intersecting beams when a line is almost vertical", () => {
+  let a = new freesewing.Point(225.72, 241);
+  let b = new freesewing.Point(225.71999999999997, 600);
+  let i = utils.beamIntersectsY(a, b, 400);
+  expect(round(i.y)).to.equal(400);
+});
+