fix(core): Fix bug in path.shiftAlong

This bug would be triggered by an edge-case where we have a path
that is made up of multiple curves/lines.

If the distance to shift lies just beyond the end of one segment,
yet the remaining distance is smaller than the step (by default
that means smaller than 1/25mm) no point would be returned.

This closes #1140

CHANGELOG.md

@@ -52,6 +52,12 @@
 
  - Correctly load saved value for mm options See [#1136](https://github.com/freesewing/freesewing/issues/1136)
 
+### core
+
+#### Fixed
+
+ - Fix a bug in `path.shiftAlong` where no point is returned if the distance to shift is a fraction of one step (1/25mm) into a new path segment See [#1140](https://github.com/freesewing/freesewing/issues/1140)
+
 ### diana
 
 #### Changed

config/changelog.yaml

@@ -46,6 +46,11 @@
     components:
       - Correctly load saved value for mm options
         See [#1136](https://github.com/freesewing/freesewing/issues/1136)
+    core:
+      - Fix a bug in `path.shiftAlong` where no point is returned if the
+        distance to shift is a fraction of one step (1/25mm) into a new
+        path segment
+        See [#1140](https://github.com/freesewing/freesewing/issues/1140)
     paco:
       - The waistband was incorrectly using the cuff widht
         See [#1113](https://github.com/freesewing/freesewing/issues/1113)

packages/core/CHANGELOG.md

@@ -1,6 +1,12 @@
 # Change log for: @freesewing/core
 
 
+## 2.17.0 (NaN-NaN-NaN)
+
+### Fixed
+
+ - Fix a bug in `path.shiftAlong` where no point is returned if the distance to shift is a fraction of one step (1/25mm) into a new path segment See [#1140](https://github.com/freesewing/freesewing/issues/1140)
+
 ## 2.15.2 (2021-04-28)
 
 ### Fixed

packages/core/src/path.js

@@ -429,8 +429,9 @@ Path.prototype.shiftAlong = function (distance, stepsPerMm = 25) {
     let op = this.ops[i]
     if (op.type === 'line') {
       let thisLen = op.to.dist(current)
+      if (Math.abs((len + thisLen) - distance) < 0.1) return op.to
       if (len + thisLen > distance) return current.shiftTowards(op.to, distance - len)
-      else len += thisLen
+      len += thisLen
     } else if (op.type === 'curve') {
       let bezier = new Bezier(
         { x: current.x, y: current.y },
@@ -439,9 +440,9 @@ Path.prototype.shiftAlong = function (distance, stepsPerMm = 25) {
         { x: op.to.x, y: op.to.y }
       )
       let thisLen = bezier.length()
-      if (len + thisLen > distance)
-        return shiftAlongBezier(distance - len, bezier, thisLen * stepsPerMm)
-      else len += thisLen
+      if (Math.abs((len + thisLen) - distance) < 0.1) return op.to
+      if (len + thisLen > distance) return shiftAlongBezier(distance - len, bezier, thisLen * stepsPerMm)
+      len += thisLen
     }
     current = op.to
   }

packages/core/tests/path.test.js

@@ -775,3 +775,23 @@ it("Should overwrite a path attribute", () => {
   expect(a.paths.line.attributes.get("class")).to.equal("overwritten");
 });
 
+it("Should move along a path even if it lands just on a joint", () => {
+  let pattern = new freesewing.Pattern();
+  pattern.parts.a = new pattern.Part();
+  let a = pattern.parts.a;
+
+  a.paths.curve = new a.Path()
+    .move(new a.Point(20.979322245694167, -219.8547313525503))
+    ._curve(
+      new a.Point(35.33122482627704, -153.54225517257478),
+      new a.Point(61.99376179214562, -105.99242252587702)
+    )
+    .curve(
+      new a.Point(88.85254026593002, -58.092613773317105),
+      new a.Point(136.13264764576948, -11.692646171119936),
+      new a.Point(170.69593749999996, -4.180844669736632e-14)
+    )
+  a.points.test = a.paths.curve.shiftAlong(121.36690836797631)
+  expect(a.points.test).to.be.instanceOf(a.Point)
+  console.log({test: a.points.test})
+})