Some question about self-intersect polygon

[jt-chairman]

1. How to judge a polygon whether it is a simple polygon or it self-intersects? Is there a API?
2. If a polygon is self-intersect, can we break this polygon into sub-polygons?

[AngusJohnson]

How to judge a polygon whether it is a simple polygon or it self-intersects? Is there a API?

No. Sorry.

If a polygon is self-intersect, can we break this polygon into sub-polygons?

  Paths64 subject = { MakePath({ 10,10, 90,90, 90,10, 10,90 }) };
  subject = Union(subject, FillRule::NonZero);
  std::cout << subject << std::endl;

50,50 , 10,90 , 10,10
90,90 , 50,50 , 90,10

[jt-chairman]

haha, so pleased to receive your reply, thank you for the library developing and sharing.

[wxy-creat]

Hello, I also want to break a self-intersection polygon into sub-polygons, and my code is:

Paths64 subject = { MakePath({ 6,0, 8,2, 8,0, 6,2 }) };
subject = Union(subject, FillRule::NonZero);
std::cout << subject << std::endl;

but the union result is empty, looks like the winding numbers of each polygon sub-region is zero.
I think the golden result should contain two sub polygons, {(6, 0), (7, 1), (6, 2)}, {(8, 0), (8, 2), (7, 1)}

Is there anything wrong with my code?

The input subject is as follows

@AngusJohnson

[AngusJohnson]

"Given that integer imprecision is constant at ±1 unit, it's important to note that the library won't return reliable solutions whenever subject or clip polygons have very small segment lengths and near zero areas. For example, a triangle with one edge that's 1 unit in length could be considered within a rounding error of having zero area. That triangle would be treated as if it were an empty polygon and ignored."
https://www.angusj.com/clipper2/Docs/Robustness.htm

[wxy-creat]

Thanks a lot.
But I'm still a little confused. In this case, the area of the sub triangle is 1 and the min length is 1.414 (sqrt(2)), which is greater than 1 unit, it would still be treated as if it were an empty polygon and ignored?

[zhuangwuangmua]

Hello, how did it work out in the end?