bbiwarg-original/bbiwarg/Utility/Quadrangle.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

using System.Drawing;

namespace bbiwarg.Utility
{
    class Quadrangle
    {
        public Quadrangle(Vector2D[] vertices)
        {
            Vertices = vertices;
        }

        public Vector2D[] Vertices
        {
            private set;
            get;
        }

        public Vector2D getRelativePosition(Vector2D p)
        {
            Vector2D a = Vertices[0];
            Vector2D b = Vertices[1];
            Vector2D c = Vertices[2];
            Vector2D d = Vertices[3];

            float C = (a.Y - p.Y) * (d.X - p.X) - (a.X - p.X) * (d.Y - p.Y);
            float B = (a.Y - p.Y) * (c.X - d.X) + (b.Y - a.Y) * (d.X - p.X) - (a.X - p.X) * (c.Y - d.Y) - (b.X - a.X) * (d.Y - p.Y);
            float A = (b.Y - a.Y) * (c.X - d.X) - (b.X - a.X) * (c.Y - d.Y);

            float D = B * B - 4 * A * C;

            float u = (-B - (float) Math.Sqrt(D)) / (2 * A);

            float p1x = a.X + (b.X - a.X) * u;
            float p2x = d.X + (c.X - d.X) * u;
            float px = p.X;

            float v = (px - p1x) / (p2x - p1x);

            return new Vector2D(v, u);
        }
    }
}