using UnityEngine;
/// <summary>
/// 一个点和一个方向可以确定一条射线
/// </summary>
public struct Ray3D
{

    public Vector3 position;
    public Vector3 direction;

    public Ray3D(Vector3 p, Vector3 d)
    {
        position = p;
        direction = d;
    }

    public static bool IsRayIntersectionPlane(Ray3D ray, Plane3D plane, ref float t)
    {

        float _a = plane.normal.x * plane.point.x
                 + plane.normal.y * plane.point.y
                 + plane.normal.z * plane.point.z;

        float _b = plane.normal.x * ray.position.x
                 + plane.normal.y * ray.position.y
                 + plane.normal.z * ray.position.z;

        float _c = plane.normal.x * ray.direction.x
                 + plane.normal.y * ray.direction.y
                 + plane.normal.z * ray.direction.z;

        t = (_a - _b) / _c;

        return t >= 0;
    }

    public static bool IsRayIntersectQuadrAngle(Ray3D ray,
                                                QuadrAngle3D quadrAngle,
                                                ref float t,
                                                ref float u,
                                                ref float v)
    {
        for (int i = 0; i < quadrAngle.triangles.Length; ++i)
        {
            if (IsRayIntersectTriangle(ray,
                                       quadrAngle.triangles[i],
                                       ref t,
                                       ref u,
                                       ref v))
            {
                return true;
            }
        }

        return false;
    }

    public static bool IsRayIntersectTriangle(Ray3D ray,
                                              Vector3 p1,
                                              Vector3 p2,
                                              Vector3 p3,
                                              ref float t,
                                              ref float u,
                                              ref float v)
    {
        Vector3 _e1 = p2 - p1;
        Vector3 _e2 = p3 - p1;
        Vector3 _p = Vector3.Cross(ray.direction, _e2);

        float _determinant = Vector3.Dot(_e1, _p);

        Vector3 _T;
        if (_determinant > 0)
        {
            _T = ray.position - p1;
        }
        else
        {
            _T = p1 - ray.position;
            _determinant = -_determinant;
        }

        if (_determinant < 0.0001f)
        {
            return false;
        }

        u = Vector3.Dot(_T, _p);
        if (u < 0 || u > _determinant)
        {
            return false;
        }

        Vector3 _q = Vector3.Cross(_T, _e1);
        v = Vector3.Dot(ray.direction, _q);
        if (v < 0 || u + v > _determinant)
        {
            return false;
        }

        t = Vector3.Dot(_e2, _q);

        float _fInvDet = 1.0f / _determinant;
        t *= _fInvDet;
        u *= _fInvDet;
        v *= _fInvDet;

        return true;

    }

    public static bool IsRayIntersectTriangle(Ray3D ray,
                                              Triangle3D triangle,
                                              ref float t,
                                              ref float u,
                                              ref float v)
    {

        return IsRayIntersectTriangle(ray,
                                      triangle.point1,
                                      triangle.point2,
                                      triangle.point3,
                                      ref t,
                                      ref u,
                                      ref v);
    }
}