Incorrect empty offset result

[LarsSkiba]

Hello,

we have encountered a problem with the ClipperOffset. This example provides a minimized input to reproduce the issue. The output is empty, even there is a CCW contour clearly greater then the offset.

This input is the result of a previous Simplify call using the same scaling. Another internal algorithm marks one of the contours as incorrect oriented given the nesting.
It is hard to judge whether this is correct or not, since they are such tiny artifacts and a visualization with floats is not conclusive. Playing around with different input scaling, we found that the problem depends a lot on the scaling value.

Nevertheless in my opinion the output should never be empty independent of the orientation of the tiny contour.

The 2nd contour is not needed to reproduce the example, but is maybe interesting to further evaluate, ifthe output of the Simplify is correct or not.

#include "clipper2/clipper.h"
int main()
{
	const double offset = -1e-3;
	const double scaling = 16777216;
	const double miterLimit = 1e4;
	const auto joinType = Clipper2Lib::JoinType::Miter;
	const auto endType = Clipper2Lib::EndType::Polygon;

	Clipper2Lib::ClipperOffset offsetter(miterLimit);
	Clipper2Lib::Paths64 paths(
		{Clipper2Lib::Path64(
			 {Clipper2Lib::Point64(-144099049, 612029194),
			  Clipper2Lib::Point64(-143880659, 612022343),
			  Clipper2Lib::Point64(-143476543, 612009666),
			  Clipper2Lib::Point64(-143399347, 612007244)}),
		 Clipper2Lib::Path64(
			 {Clipper2Lib::Point64(-143476543, 612009666),
			  Clipper2Lib::Point64(-143669378, 612015715),
			  Clipper2Lib::Point64(-143384594, 612006781)}),
		 Clipper2Lib::Path64(
			 {Clipper2Lib::Point64(-303982567, -352887774),
			  Clipper2Lib::Point64(450248930, -352887774),
			  Clipper2Lib::Point64(450248930, 609421831),
			  Clipper2Lib::Point64(-303982567, 609421831),
			  Clipper2Lib::Point64(-303982567, -352887774)})});

	offsetter.AddPaths(paths, joinType, endType);

	Clipper2Lib::Paths64 resultPaths;
	offsetter.Execute(offset * scaling, resultPaths);
}

Would be great if you could have a look into it.
Thanks, Lars

[AngusJohnson]

Hi Lars.
Thanks for the feedback.
I can see, and am now addressing this and a number of other problems I've found in ClipperOffset.
Stay tuned 😁.

[AngusJohnson]

Hopefully fixed now.