2D空间中判断一点是否在三角形内

时间：2022-04-14 13:04:44

要注意如果是XY坐标轴的2D空间，要取差乘分量z而不是y。

实现原理是，将三角形ABC三个边(AB,BC,CA)分别与比较点判断差乘，如果这3个差乘结果表示的方向一致，说明就在三角形内。

效果：

2D空间中判断一点是否在三角形内

代码(Unity3D)：

using UnityEngine;

using System.Collections;

using System.Collections.Generic;

public class TriangleCollider : MonoBehaviour

{

    public const float ERROR = 0.05f;

    public Transform trianglePoint1;

    public Transform trianglePoint2;

    public Transform trianglePoint3;

    public Transform comparePoint;

    public bool IsContract(Vector3 comparePoint)

    {

        var dir1 = trianglePoint2.position - trianglePoint1.position;

        var dir2 = trianglePoint3.position - trianglePoint2.position;

        var dir3 = trianglePoint1.position - trianglePoint3.position;

        var cross1 = Mathf.Sign(Vector3.Cross(dir1, comparePoint - trianglePoint1.position).y);

        var cross2 = Mathf.Sign(Vector3.Cross(dir2, comparePoint - trianglePoint2.position).y);

        var cross3 = Mathf.Sign(Vector3.Cross(dir3, comparePoint - trianglePoint3.position).y);

        var dir = Mathf.Approximately(cross1, cross2) ? cross3 : Mathf.Approximately(cross1, cross3) ? cross2 : cross1;

        cross1 = Mathf.Sign(Vector3.Cross(dir1, comparePoint - trianglePoint1.position).y + -dir * ERROR);

        cross2 = Mathf.Sign(Vector3.Cross(dir2, comparePoint - trianglePoint2.position).y + -dir * ERROR);

        cross3 = Mathf.Sign(Vector3.Cross(dir3, comparePoint - trianglePoint3.position).y + -dir * ERROR);

        return Mathf.Approximately(cross1, cross2) && Mathf.Approximately(cross2, cross3);

    }

    void OnDrawGizmos()

    {

        if (comparePoint == null) return;

        var oldColor = Gizmos.color;

        if (IsContract(comparePoint.position))

            Gizmos.color = Color.red;

        Gizmos.DrawLine(trianglePoint1.position, trianglePoint2.position);

        Gizmos.DrawLine(trianglePoint2.position, trianglePoint3.position);

        Gizmos.DrawLine(trianglePoint3.position, trianglePoint1.position);

        Gizmos.color = oldColor;

    }

}

为了加误差，所以多做了3次差乘。不过使用起来还算可以

相关文章