Path3D edge case fix

dist/preview release/what's new.md

@@ -218,6 +218,7 @@
 - Fixed missing properties in serialization / parsing of `coneParticleEmitter` ([Popov72](https://github.com/Popov72))
 - Fix a bug with exit VR and Edge ([RaananW](https://github.com/RaananW/))
 - Fixed an issue with size of texture in multiview ([RaananW](https://github.com/RaananW/))
+- Fixed Path3D (bi)normals computation for specific edge cases ([Poolminer](https://github.com/Poolminer/))
 
 ## Breaking changes
 

src/Maths/math.path.ts

@@ -616,6 +616,7 @@ export class Path3D {
         var cur: Vector3;         // current vector (segment)
         var curTang: Vector3;     // current tangent
         // previous normal
+        var prevNor: Vector3;    // previous normal
         var prevBinor: Vector3;   // previous binormal
 
         for (var i = 1; i < l; i++) {
@@ -631,8 +632,12 @@ export class Path3D {
             // normals and binormals
             // http://www.cs.cmu.edu/afs/andrew/scs/cs/15-462/web/old/asst2camera.html
             curTang = this._tangents[i];
+            prevNor = this._normals[i - 1];
             prevBinor = this._binormals[i - 1];
             this._normals[i] = Vector3.Cross(prevBinor, curTang);
+            if (this._normals[i].length() === 0) {
+                this._normals[i] = prevNor;
+            }
             if (!this._raw) {
                 this._normals[i].normalize();
             }