Potential bug when offsetting paths containing a single point.

[JimBobSquarePants]

I thought I better ask this here first before raising an issue, but I think I may have found a small bug in how single point paths are handled.

When building the Rect64 instance here it appears to me that the delta is applied to the given coordinated incorrectly.

Clipper2/CSharp/Clipper2Lib/Clipper.Offset.cs

Lines 672 to 683 in 2310524

	}
	else
	{
	int d = (int) Math.Ceiling(_groupDelta);
	Rect64 r = new Rect64(path[0].X - d, path[0].Y - d,
	path[0].X - d, path[0].Y - d);
	group.outPath = r.AsPath();
	#if USINGZ
	group.outPath = InternalClipper.SetZ(group.outPath, path[0].Z);
	#endif
	}
	group.outPaths.Add(group.outPath);

Given that a path is centered at the offset I would expect the following offset for the left/top/right/bottom parameters.

l - d
t - d
r + d
b + d

Have I missed something?

[AngusJohnson]

      Paths64 subject = new(), solution = new();
      subject.Add(Clipper.MakePath(new int[] { 0,0 }));
      ClipperOffset clipperOffset = new ClipperOffset();
      clipperOffset.AddPaths(subject, JoinType.Round, EndType.Round);
      clipperOffset.Execute(10, solution);

      SvgWriter svg = new SvgWriter();
      SvgUtils.AddOpenSubject(svg, subject);
      SvgUtils.AddSolution(svg, solution, false);
      string filename = @"..\..\..\tmp.svg";
      SvgUtils.SaveToFile(svg, filename, FillRule.NonZero, 600, 400, 100);
      ClipperFileIO.OpenFileWithDefaultApp(filename);

Remember that this must be an open path, so the offset specifies the width of the open path (ie a line).
So the "offset" (or delta) of a single point 'line' will be the diameter of solution path (not its radius).

[JimBobSquarePants]

Endtype.Round looks correct, it’s when generating a square for other end types. The link I posted is to the latest source as of last night.

d appears to be subtracted for all four sides.

[AngusJohnson]

Oh, yeah, that new Rect64(...) construct is definitely wrong (right, and bottom should have pluses) 😱.

[JimBobSquarePants]

That makes up for my silly issue the other day then 🙂