Clipping operation causes crash

[SHKnudsen]

Hi,

Im still very new to Clipper so i assume that im doing something weird here. Im getting a crash when running a unit test that perform some clipping operations, everything works great until this specific scenario.

Im using ClipperD to execute an intersection, the Subject consists of 6 polygons and the Clip has 1. Below ive tried to illustrate the scenario (yellow is the subject and red is the clip):

Here's a zoomed-in image of the part where the clip path meets the middle part of the subject paths:

As metioned when executing the test host simply crashes, but the logs gives me the following:

The active test run was aborted. Reason: Test host process crashed : Stack overflow.
Repeat 4802 times:
--------------------------------
   at Clipper2Lib.ClipperBase.RecursiveCheckOwners(Clipper2Lib.OutRec, Clipper2Lib.PolyPathBase)
--------------------------------
   at Clipper2Lib.ClipperBase.DeepCheckOwners(Clipper2Lib.OutRec, Clipper2Lib.PolyPathBase)
   at Clipper2Lib.ClipperBase.BuildTree(Clipper2Lib.PolyPathBase, Clipper2Lib.Paths64)
   at Clipper2Lib.ClipperD.Execute(Clipper2Lib.ClipType, Clipper2Lib.FillRule, Clipper2Lib.PolyTreeD, Clipper2Lib.PathsD)
   at Clipper2Lib.ClipperD.Execute(Clipper2Lib.ClipType, Clipper2Lib.FillRule, Clipper2Lib.PolyTreeD)

Heres a snippet of my code:

var regionPaths = new PathsD();
visibleRegions.ForEach(x => regionPaths.AddRange(Clipper.PolyTreeToPathsD(x.Item1)));

var solution = new PolyTreeD();
var clipper = new ClipperD
{
    PreserveCollinear = false,
};
clipper.AddSubject(Clipper.PolyTreeToPathsD(face.Polygon));
clipper.AddClip(regionPaths);
clipper.Execute(ClipType.Intersection, FillRule.NonZero, solution);

Im a bit lost about what could be causing this, so if anyone has some inputs that would be greatly appreciated!

[AngusJohnson]

Hi Sylvester.
I can't help unless you provide the polygon data that causes the crash.

[SHKnudsen]

Of course sorry about that.

let me know of this works or if you need it in a different way:

PathsD subj = new PathsD();
PathsD clip = new PathsD();

subj.Add(Clipper.MakePath(new double[] { 2217.08, -44400.32, 2217.08, -44385.16, 1992.08, -44385.16, 1992.08, -44403.69, 1992.08, -44415.47, 2217.08, -44415.47 }));

clip.Add(Clipper.MakePath(new double[] { 2217.08, -44208.84, 1992.08, -44208.84, 1992.08, -44468.84, 2217.08, -44468.84 }));
clip.Add(Clipper.MakePath(new double[] { 2076.91, -44288.21, 2117.81, -44288.21, 2117.81, -44415.05, 2076.91, -44415.05 }));
clip.Add(Clipper.MakePath(new double[] { 2117.81, -44288.21, 2103.21, -44288.21, 2103.21, -44399.40, 2117.81, -44406.72 }));
clip.Add(Clipper.MakePath(new double[] { 2091.52, -44399.40, 2091.52, -44288.21, 2076.91, -44288.21, 2076.91, -44406.72 }));
clip.Add(Clipper.MakePath(new double[] { 2103.21, -44288.21, 2091.52, -44288.21, 2091.52, -44399.40, 2103.21, -44399.40 }));
clip.Add(Clipper.MakePath(new double[] { 2117.81, -44406.72, 2103.21, -44399.40, 2091.52, -44399.40, 2076.91, -44406.72, 2076.91, -44415.05, 2117.81, -44415.05 }));

var solution = new PolyTreeD();
var clipper = new ClipperD
{
    PreserveCollinear = false,
};
clipper.AddSubject(subj);
clipper.AddClip(clip);
clipper.Execute(ClipType.Intersection, FillRule.NonZero, solution);

[AngusJohnson]

Thanks Sylvester.
Yes, there appears to be a bug that's specific to the C# translation. I'll fix ASAP.

[SHKnudsen]

Thanks for the quick reply!

[AngusJohnson]

Clipper2/CSharp/Clipper2Lib/Clipper.Engine.cs

Lines 3290 to 3292 in 4b02bb9

	public bool Execute(ClipType clipType, FillRule fillRule, PolyTreeD polytree, PathsD openPaths)
	{
	polytree.Clear();

At line 3293, insert the following line:
_using_polytree = true;

[SHKnudsen]

Absolute legend!

just tested out on latest main and everything seems to work now. Do you know when this will be published to nuget?

Also, thanks for this quick fix much appreciated.

[SHKnudsen]

Not sure if this is related, but when using the latest main i am now getting some unexpected behavior when creating PolyTreeDs:

PathsD subj = new PathsD();

subj.Add(Clipper.MakePath(new double[] {1760.55,-44338.84, 1760.55,-44113.84, 1935.92,-44113.84, 1935.92,-44338.84 }));
subj.Add(Clipper.MakePath(new double[] {1814.09,-44254.01, 1814.09,-44213.11, 1899.64,-44213.11, 1899.64,-44254.01 }));

PolyTreeD polytree = new();
ClipperD clipper = new();
clipper.AddSubject(subj);
clipper.Execute(ClipType.Union, FillRule.NonZero, polytree);

I expected this to return a tree where the second subject would be a child of the first, instead i get a 1 level tree only with the first subject:

[AngusJohnson]

The winding direction of your second path (that's a nested polygon contour) is in the same direction as the first (outer) path.
So a Union op on these polygons will strip the inner path unless you change the fillrule to EvenOdd.