Request: a release with the FixSelfIntersects fix (#1067). Difference loses most of its area in 2.0.0 and 2.0.1 (NonZero, C#) #1122

Summary

Clipper.Difference with FillRule.NonZero, on a simple five-vertex subject and a simple triangle clip, returns 29,655,090.5 square units where the exact answer is 135,974,247. Almost 80% of the result is missing, including points well inside the subject and outside the clip. Commit 4da1564 on main ("Fixed a bug in ClipperBase::FixSelfIntersects (#1067)", 2026-02-22) fixes this input. No release contains that commit yet: NuGet's newest is 2.0.0 and the newest tag is 2.0.1. This issue asks for one, and offers the input below as a regression test.

Versions

Input

Integer coordinates, one path each, both simple.

subject: (-503, 4889) (40000, 20000) (34522, 23202) (61000, 41700) (-4000, 3200)
clip:    (63046, 38116) (0, 10000) (-556, 4862)

Expected and actual

The point (22716, 15000) is inside the subject and outside the clip, but outside every path of the result.

Reproduction (C#, NuGet Clipper2 2.0.0 only)

using Clipper2Lib;

// A simple five-vertex subject and a simple triangle clip.
var subject = new Paths64 { Clipper.MakePath(new long[]
    { -503, 4889, 40000, 20000, 34522, 23202, 61000, 41700, -4000, 3200 }) };
var clip = new Paths64 { Clipper.MakePath(new long[]
    { 63046, 38116, 0, 10000, -556, 4862 }) };
Paths64 difference = Clipper.Difference(subject, clip, FillRule.NonZero);

Console.WriteLine($"Clipper2 {typeof(Clipper).Assembly.GetName().Version}");
Console.WriteLine($"subject area:    {Clipper.Area(subject)}");
Console.WriteLine($"clip area:       {Clipper.Area(clip)}");
Console.WriteLine($"difference area: {Clipper.Area(difference)}");

// (22716, 15000) is inside the subject and outside the clip,
// so it belongs in the difference; the result leaves it out.
var probe = new Point64(22716, 15000);
Console.WriteLine($"probe vs subject: {Clipper.PointInPolygon(probe, subject[0])}");
Console.WriteLine($"probe vs clip:    {Clipper.PointInPolygon(probe, clip[0])}");
bool inResult = false;
foreach (Path64 path in difference)
{
    var where = Clipper.PointInPolygon(probe, path);
    Console.WriteLine($"probe vs output:  {where} (output path area {Clipper.Area(path)})");
    if (where == PointInPolygonResult.IsInside) inResult = !inResult;
}
Console.WriteLine(inResult ? "ok" : "FAIL: the difference lost a point it should keep");
return inResult ? 0 : 1;

Output with 2.0.0:

subject area:    200159500
clip area:       154148926
difference area: 29655090.5
probe vs subject: IsInside
probe vs clip:    IsOutside
probe vs output:  IsOutside (output path area 29058161)
probe vs output:  IsOutside (output path area -59761)
probe vs output:  IsOutside (output path area 656690.5)
FAIL: the difference lost a point it should keep

Notes

• 4da1564 removes the "adjacent intersections (ie a micro self-intersection)" shortcut in FixSelfIntersects, so the cleanup goes through DoSplitOp. On this input the old shortcut drops a large part of the outline.
• The input was reduced automatically from a larger real case: 31 vertices in three paths, losing about 190,000 units in 1,150,000. The reduction drops a path or a vertex, rounds a coordinate, or moves or scales the whole input, and keeps each change only while the difference still loses area. It is a local minimum, not necessarily the smallest failing input.
• Checked against this repository on 2026-10-26: Clipper2_2.0.1 (21ebba0) is 7 commits behind 4da1564 and does not contain it.

Found by an automated soak test, and reduced and analysed with AI assistance; the repro and its numbers were run and checked as given above.