Difference in Results Between Clipper and Clipper2

[aarmol]

Hi,

While trying to convert my code that is currently using the Clipper library to Clipper2 I noticed a difference between these two libraries when performing a polygon difference operation. The following (test)code gives me the expected result when using the 'Clipper' library, but the result with Clipper2 remains empty.

using Clipper:

List<IntPoint> testPath = [ new(0, 0), new(100, 0), new(100, 100), new(0, 100), new(0, 0)];
List<IntPoint> clipPath = [ new(50, 25), new(150, 25), new(150, 75), new(50, 75)];

ClipperLib.Clipper cl = new();
PolyTree result = new();
cl.AddPath(testPath, PolyType.ptSubject, Closed: false);
cl.AddPath(clipPath, PolyType.ptClip, Closed: true);
cl.Execute(ClipperLib.ClipType.ctDifference, result);

// The result I'm getting:
// result.ChildCount = 2
// result.Child[0].Contour = (100, 75),(100, 100),(0, 100),(0, 0)
// result.Child[1].Contour = (0, 0),(100, 0),(100, 25)

using Clipper2:

Path64 testPath2 = Clipper2Lib.Clipper.MakePath((int[])[0, 0, 100, 0, 100, 100, 0, 100, 0, 0]);
Path64 clipPath2 = Clipper2Lib.Clipper.MakePath((int[])[50, 25, 150, 25, 150, 75, 50, 75]);

Clipper64 cl2 = new();
PolyTree64 result2 = new();
cl2.AddOpenSubject(testPath2);
cl2.AddClip(clipPath2);
cl2.Execute(Clipper2Lib.ClipType.Difference, Clipper2Lib.FillRule.EvenOdd, result2);

// The result:
// result2.Count = 0

Any insights or suggestions on what might be causing this ? Thanks!

[vectorstorm]

You've likely already found this on your own, but since nobody has replied..

From the PolyTree64 documentation:

PolyTree64 will never contain open paths (unlike in Clipper1) since open paths can't contain [child] paths. When clipping open paths, these will always be represented in solutions via a separate Paths64 structure.

It doesn't make sense to put open paths into a PolyTree object, since open paths can't contain other objects (which is kind of the whole point of using a PolyTree in the first place; to capture the parent/child relationships of result polygons)

You want to instead call the variant of cl2.Execute() with a Paths64 object to receive the results, instead of using a PolyTree64; that should give you the open path segments you want. (also, it'll probably be faster!)