ConcavePolygonShape2D

ConcavePolygonShape2D stores independent segments rather than a filled polygon. Segments=[A,B,C,D] defines only A–B and C–D. Connections B–C and D–A are not added automatically. Even when segments form a closed contour, a small shape entirely inside it does not intersect the boundary and produces no overlap in a direct query.

For four corners A,B,C,D, a closed contour requires [A,B,B,C,C,D,D,A]. This complete executed helper builds it from a corner list. Supply each corner once, without repeating the first at the end. The caller owns the returned resource:

using System;
using Reckfell;

public static class ContourFactory2D
{
    // Boundary only: this does not fill the enclosed area or check self-intersections.
    // Supply each corner once; the last edge is added here. Caller owns the resource.
    public static ConcavePolygonShape2D Closed(ReadOnlySpan<Vector2> corners)
    {
        if (corners.Length < 3)
            throw new ArgumentException("At least three corners are required.", nameof(corners));
        var segments = new Vector2[checked(corners.Length * 2)];
        for (int i = 0; i < corners.Length; i++)
        {
            Vector2 a = corners[i];
            Vector2 b = corners[(i + 1) % corners.Length];
            if (!float.IsFinite(a.X) || !float.IsFinite(a.Y) || a == b)
                throw new ArgumentException("Corners must be finite and adjacent corners distinct.", nameof(corners));
            segments[2 * i] = a;
            segments[2 * i + 1] = b;
        }
        var shape = new ConcavePolygonShape2D();
        shape.SetSegments(segments.AsSpan());
        return shape;
    }
}

The helper validates corner count, finite coordinates and nonzero edge lengths. It does not validate self-intersections, area or artistic contour correctness, and does not fill the contour. Use ConvexPolygonShape2D for a filled convex object; split a filled concave shape into convex pieces.

A new resource is empty. Segments must have an even element count; an empty array clears geometry. The getter returns an independent array that must be assigned back after editing. Both SetSegments overloads copy input. Changed is emitted even for repeated data. GetRect() encloses all endpoints in local coordinates, but a point inside those bounds does not necessarily collide with a segment.

For a collider, assign the resource to Shape on CollisionShape2D, which must be a direct child Entity of CollisionObject2D. A resource alone adds no body to the world.

Arrays and ReadOnlySpan, independent copies, clearing, local bounds, Changed and the exact helper were checked. Direct queries confirmed an empty closed-square interior, collision at its edge and no collision with a separated circle. Body movement, continuous fast-collision detection, performance and drawing were not tested.

Declarations checked against C# SDK 1.0.0. Expand a name to see declarations and documentation.

public ConcavePolygonShape2D();

public Vector2[] Segments { get; set; }

public Vector2[] GetSegments();

public void SetSegments(Vector2[] segments);

public void SetSegments(ReadOnlySpan<Vector2> segments);