Inconsistent results for tessellation

[JSeligstein]

Hey there. I am generating a random shape through the following process:

• Choose n points around a circle with random radius r from (minR, maxR)
• Create a spline connecting those points
• Create a polygon by sampling that spline at m points around the circle.

I'm then passing that shape into tessellation with maxEdge being 0.5, though I've seen similar results at 1.0.

I get relatively inconsistent results. Sometimes, it tessellates beautifully:

Sometimes, it half is tessellated, half is fanned:

Sometimes it just gets full fan treatment:

No code has changed between these screenshots, but the random shape has obviously changed. I would expect closer to the first one for all results.

// returns Vector2[] polygon
var polygon = section.splineToPolygon();
var iGeom = IntGeom.DefGeom;
var extraPoints = new NativeArray<IntVector>(0, Allocator.Temp);

// copied from sample code
var pShape = ToPlainShape(polygon, null, iGeom, Allocator.Temp);
var delaunay = pShape.Delaunay(iGeom.Int(0.f5), extraPoints, Allocator.Temp);
delaunay.Tessellate(iGeom, 1.0f);

extraPoints.Dispose();
            
var triangles = delaunay.Indices(Allocator.Temp);
_triangles.AddRange(triangles);

var vertices = delaunay.Vertices(Allocator.Temp, iGeom, 0);
foreach (var vtx in vertices) {
    _vertices.Add(new Vector3(vtx.x, 0f, vtx.y)-this._worldPos);
}

delaunay.Dispose();

[JSeligstein]

@NailxSharipov any idea here?

Here's a small reproducible example in the Scene window. As you increase numPoints, it fails to tessellate anymore and just defaults to a fan. On my computer, this succeeds in a tessellation at 47 points, but fails at 48 and above.

using UnityEngine;
using Unity.Collections;
using iShape.Geometry;
using iShape.Geometry.Container;
using iShape.Triangulation.Shape.Delaunay;
using System;

namespace Jags.Debug {
    public static class TessellationDebug {

        public static void drawCircleFailure() {
            // generate circle polygon
            int numPoints = 50;
            float radius = 15f;
            Vector2[] polygon = new Vector2[numPoints];
            for (int p = 0; p < numPoints; p++) {
                // generate point around circle clockwise
                float radians = -2f * Mathf.PI * (float)p / (float)numPoints;
                polygon[p].Set(Mathf.Cos(radians) * radius, Mathf.Sin(radians) * radius);
            }

            // tessellate
            IntGeom iGeom = IntGeom.DefGeom;
            IntVector[] iHull = iGeom.Int(polygon);
            IntShape iShape = new IntShape(iHull, Array.Empty<IntVector[]>());
            PlainShape pShape = new PlainShape(iShape, Allocator.Temp);
            Delaunay delaunay = pShape.Delaunay(iGeom.Int(1f), Allocator.Temp);
            delaunay.Tessellate(iGeom, 1f);
            
            NativeArray<int> triangles = delaunay.Indices(Allocator.Temp);
            NativeArray<Vector3> vertices = delaunay.Vertices(Allocator.Temp, iGeom, 0);

            // draw debug vertices
            foreach (Vector3 vert in vertices) {
                // draw debug sphere
                GameObject g = GameObject.CreatePrimitive(PrimitiveType.Sphere);
                g.transform.localScale = Vector3.one * 0.1f;
                g.transform.position = vert;
            }

            // draw triangles
            for (int tdx = 0; tdx < triangles.Length/3; tdx++) {
                UnityEngine.Debug.DrawLine(vertices[triangles[tdx*3]], vertices[triangles[tdx*3+1]], Color.red, 100000f);
                UnityEngine.Debug.DrawLine(vertices[triangles[tdx*3+1]], vertices[triangles[tdx*3+2]], Color.red, 100000f);
                UnityEngine.Debug.DrawLine(vertices[triangles[tdx*3+2]], vertices[triangles[tdx*3]], Color.red, 100000f);
            }
        }
    }
}