PointInPolygon2D

PointInPolygon2D.cs

using TMPro;
using UnityEngine;

public class PointInPolygon2D : MonoBehaviour
{
    public Transform point;
    public PolygonCollider2D polygon;

    public TextMeshProUGUI statusText;

    Vector2[] verts;
    SpriteRenderer sr;

    void Start()
    {
        sr = point.GetComponent<SpriteRenderer>();
        verts = polygon.points;
    }

    void Update()
    {
        Vector2 lineStart = point.position;
        Vector2 lineEnd = point.position + Vector3.up * -999;
        Debug.DrawLine(lineStart, lineEnd, Color.gray);

        int hitCount = 0;

        // loop lines in collider
        for (int i = 0; i < verts.Length; i++)
        {
            var vertStart = polygon.transform.InverseTransformPoint(verts[i]);
            var vertEnd = polygon.transform.InverseTransformPoint(verts[(i + 1) % verts.Length]);

            // skip if above point Y
            if (vertStart.y > lineStart.y && vertEnd.y > lineStart.y)
            {
                Debug.DrawLine(vertStart, vertEnd, Color.gray);
                continue;
            }

            // skip if start/end x is away from point x
            if ((vertStart.x < lineStart.x && vertEnd.x < lineStart.x) || (vertStart.x > lineStart.x && vertEnd.x > lineStart.x))
            {
                Debug.DrawLine(vertStart, vertEnd, Color.black);
                continue;
            }


            if (Intersects(lineStart, lineEnd, vertStart, vertEnd))
            {
                hitCount++;
                Debug.DrawLine(vertStart, vertEnd, Color.red);
            }
            else
            {
                Debug.DrawLine(vertStart, vertEnd, Color.green);
            }
        }

        if (hitCount % 2 == 0)
        {
            sr.color = Color.green;
            statusText.text = "outside";
        }
        else
        {
            sr.color = Color.red; // inside
            statusText.text = "inside";
        }

        polygon.transform.Rotate(0,0,30*Time.deltaTime);
    }


    // https://forum.unity.com/threads/line-intersection.17384/#post-4442284
    bool Intersects(Vector2 line1point1, Vector2 line1point2, Vector2 line2point1, Vector2 line2point2)
    {
        Vector2 a = line1point2 - line1point1;
        Vector2 b = line2point1 - line2point2;
        Vector2 c = line1point1 - line2point1;
        float alphaNumerator = b.y * c.x - b.x * c.y;
        float betaNumerator = a.x * c.y - a.y * c.x;
        float denominator = a.y * b.x - a.x * b.y;
        if (denominator == 0)
        {
            return false;
        }
        else if (denominator > 0)
        {
            if (alphaNumerator < 0 || alphaNumerator > denominator || betaNumerator < 0 || betaNumerator > denominator)
            {
                return false;
            }
        }
        else if (alphaNumerator > 0 || alphaNumerator < denominator || betaNumerator > 0 || betaNumerator < denominator)
        {
            return false;
        }
        return true;
    }
}