ClipperLib2 : SimplifyPolygon not available?

[Phil Stopford]

Just noticed this isn't available, that I can find. Is this unavailable; if so, what's the best way to reproduce what it did?

[Angus Johnson]

Nope, Clipper1 didn't do this well, and the code was complicated and messy, so it's been removed. There are currently no functions or methods to do this, at least until I can figure out how to do this better than it was done in Clipper1.

[Phil Stopford]

Naively, I thought this might be done by looking for angles ~180 degrees (where epsilon is the tolerance).

[Angus Johnson]

Naively, I thought this might be done by looking for angles ~180 degrees (where epsilon is the tolerance).

I'm very open to colaboration and incorporating useful code. 😁

[Phil Stopford]

I'll play with it when I get the migration sorted and start running tests. I'm limited to C# but hopefully that could still be useful; this is also why I pointed at the github repository earlier. You'll see some customizations there already :)

[Phil Stopford]

This is what I was thinking of - I had the code in my DesignLibs_GPL project so pulled this out as an idea. From inspection of ClipperLib1, the SimplifyOption was really a Union (to tidy self-intersections) and then a colinear removal. I'd assume the colinear removal is the missing part to get this going in ClipperLib2, but admit to being uncertain. This code also assumes a closed shape because that's my use case

    public static Paths stripColinear(Paths source, double angularTolerance = 0.0f)
    {
        return source.Select(t => pStripColinear(t, angularTolerance)).ToList();
    }

    public static Path stripColinear(Path source, double angularTolerance = 0.0f)
    {
        return pStripColinear(source, angularTolerance);
    }

    private static Path pStripColinear(Path source, double angularTolerance = 0.0f)
    {
        switch (source.Count)
        {
            case < 3:
                return source;
        }

        Path ret = new();

        for (int pt = 0; pt < source.Count; pt++)
        {
            Point64 interSection_A, interSection_B, interSection_C;
            switch (pt)
            {
                // Assess angle.
                case 0:
                    interSection_B = source[^1]; // map to last point
                    interSection_C = source[pt];
                    interSection_A = source[pt + 1];
                    break;
                default:
                {
                    if (pt == source.Count - 1) // last point in the list
                    {
                        interSection_B = source[pt - 1];
                        interSection_C = source[pt];
                        interSection_A = source[0]; // map to the first point
                    }
                    else
                    {
                        interSection_B = source[pt - 1];
                        interSection_C = source[pt];
                        interSection_A = source[pt + 1];
                    }

                    break;
                }
            }

            double theta = pAngleBetweenPoints(interSection_A, interSection_B, interSection_C, false);

            if (pt == 0 || Math.Abs(theta - 180) > angularTolerance)
            {
                ret.Add(new Point64(source[pt]));
            }
        }
        return ret;
    }

[Angus Johnson]

SimplifyOption was really a Union (to tidy self-intersections) and then a colinear removal.

Neither self-intersections or colinear spikes should be an issue in Clipper2.
It's the joining of touching polygons in solutions that was unsatisfactory in Clipper1 and left out of Clipper2.