GeometryUtils from Grid Terrain Video

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class GeometryUtils {

    public static float LookRotationY2D(Vector2 start, Vector2 end)
    {
        return Quaternion.LookRotation(new Vector3(end.x, 0, end.y) - new Vector3(start.x, 0, start.y)).eulerAngles.y;
    }

    public static float XZDistance(Vector3 point1, Vector3 point2)
    {
        Vector2 point12D = new Vector2(point1.x, point1.z);
        Vector2 point22D = new Vector2(point2.x, point2.z);
        return Vector2.Distance(point12D, point22D);
    }

    public static GameObject DrawDebugCircle(Vector3 pos, Color color, string name = "Circle", float scale = 2f)
    {
        GameObject obj = GameObject.CreatePrimitive(PrimitiveType.Sphere);
        obj.name = name;
        obj.transform.localScale = new Vector3(scale, scale, scale);
        obj.GetComponent<Renderer>().material.color = color;
        obj.transform.position = pos;
        obj.layer = 2;
        return obj;
    }



    private static void set(ref ColliderRect p)
    {
        double temp;
        if (p.a.x > p.b.x) { temp = p.a.x; p.a.x = p.b.x; p.b.x = temp; }
        if (p.a.y > p.b.y) { temp = p.a.y; p.a.y = p.b.y; p.b.y = temp; }
    }

    private static bool inside(ColliderRect p1, ColliderRect p2)
    {
        return (p2.a.x <= p1.a.x && p1.b.x <= p2.b.x &&
            p2.a.y <= p1.a.y && p1.b.y <= p2.b.y ? true : false);
    }

    public static  bool isPointInsideRectangle(Vector3 searchPoint, Vector3 rectPoint1, Vector3 rectPoint2)
    {
        ColliderRect p1 = new  ColliderRect( new ColliderRectPoint(searchPoint.x, searchPoint.z), new ColliderRectPoint(searchPoint.x, searchPoint.z) );
        ColliderRect p2 = new ColliderRect(new ColliderRectPoint(rectPoint1.x, rectPoint1.z), new ColliderRectPoint(rectPoint2.x, rectPoint2.z));
        set(ref p1);
        set(ref p2);
        return inside(p1, p2);
    }


    public static bool is_point_in_rectangle(List<Transform> rect, Vector3 p)
    {
        Vector2 P1= new Vector2(rect[0].position.x, rect[0].position.z);
        Vector2 P2= new Vector2(rect[1].position.x, rect[1].position.z);
        Vector2 P3= new Vector2(rect[2].position.x, rect[2].position.z);
        Vector2 P4= new Vector2(rect[3].position.x, rect[3].position.z);
        Vector2 P = new Vector3(p.x, p.z);

        Vector2 P1_P4 = P1 - P4;
        Vector2 P3_P4 = P3 - P4;
        Vector2 TWO_P_C = 2.0f * P - P1 - P3; // TWO_P_C=2P-C, C=Center of rectangle

        return (Vector2.Dot(P3_P4, TWO_P_C - P3_P4) <= 0 && Vector2.Dot(P3_P4, TWO_P_C + P3_P4) >= 0) &&
        (Vector2.Dot(P1_P4, TWO_P_C - P1_P4) <= 0 && Vector2.Dot(P1_P4, TWO_P_C + P1_P4) >= 0);
    }




}


struct ColliderRectPoint
{
    public  double x, y;
    public ColliderRectPoint(double x, double y)
    {
        this.x = x;
        this.y = y;
    }

};

struct ColliderRect
{
    public ColliderRectPoint a, b;
    public ColliderRect(ColliderRectPoint a, ColliderRectPoint b)
    {
        this.a = a;
        this.b = b;
    }

};