SpiritLink

using System.Collections;
using System.Collections.Generic;
using System.ComponentModel.Design;
using UnityEditor;
using UnityEngine;

public class PlaneLineCollision : MonoBehaviour
{

   public Transform P0;
   public Transform P1;
   public Transform P2;
   public Transform Line;

   public float dot;
   public float t;
   public float u;
   public float v;

   private void OnDrawGizmos()
   {
      Gizmos.color = Color.cyan;
      Gizmos.DrawLine(P0.position, P1.position);
      Gizmos.DrawLine(P1.position, P2.position);
      Gizmos.DrawLine(P2.position,P0.position);

      Gizmos.color = Color.red;
      Gizmos.DrawSphere(Line.position, 0.05f);

      Gizmos.color = Color.green;
      Gizmos.DrawRay(Line.position, Line.forward * 3);

      Vector3 L1 = P1.position - P0.position;
      Vector3 L2 = P2.position - P0.position;
      Vector3 Cross = Vector3.Cross(L1, L2);


      // 1, 평면의 법선 벡터와 직선의 내적을 검사, 0일경우 Pass
      
      Vector3 startPos = (P0.position + P1.position + P2.position) / 3;

      Gizmos.color = Color.yellow;
      Gizmos.DrawRay(startPos, Cross.normalized * 5);

      dot = Vector3.Dot(Line.forward, Cross.normalized);

      if (IntersectTriangle(Line.position, Line.forward, P0.position, P1.position, P2.position))
      {
         Vector3 point = Line.position + (Line.forward * t);
         Gizmos.DrawSphere(point, 0.1f);
      }

      // 2. 교점의 계산
   }

   private bool IntersectTriangle(Vector3 RayOrigin, Vector3 RayDirection, Vector3 V0, Vector3 V1, Vector3 V2)
   {
      Vector3 edge1 = V1 - V0;
      Vector3 edge2 = V2 - V0;

      Vector3 pvec = Vector3.Cross(RayDirection, edge2);

      dot = Vector3.Dot(edge1, pvec);

      Vector3 tvec;
      if (dot > 0) tvec = RayOrigin - V0;
      else
      {
         tvec = V0 - RayOrigin;
         dot = -dot;
      }

      if (dot < 0.0001f)
         return false;

      u = Vector3.Dot(tvec, pvec);
//    if (u < 0.0f || u > dot)
//       return false;

      Vector3 qvec = Vector3.Cross(tvec, edge1);

      v = Vector3.Dot(RayDirection, qvec);
//    if (v < 0.0f || u + v > dot) 
//       return false;

      t = Vector3.Dot(edge2, qvec);
      float flnvDet = 1.0f / dot;

      t *= flnvDet;
      u *= flnvDet;
      v *= flnvDet;

      return true;
   }
}