出处: 

 

测试脚本(返回值为交点数量):

using System.Collections;using System.Collections.Generic;using UnityEngine;public class LineCircleIntersect : MonoBehaviour{    public Transform a;    public Transform b;    public Transform circleCenter;    public float radius;    void OnDrawGizmos()    {        if (a == null || b == null || circleCenter == null) return;        var intersect1 = default(Vector2);        var intersect2 = default(Vector2);        var intersectCount = BetweenLineAndCircle(circleCenter.position, radius, a.position, b.position, out intersect1, out intersect2);        if (intersectCount > 0)            Gizmos.DrawWireSphere(intersect1, 0.1f);        if (intersectCount > 1)            Gizmos.DrawWireSphere(intersect2, 0.1f);        Gizmos.DrawLine(a.position, b.position);        Gizmos.DrawWireSphere(circleCenter.position, radius);    }    int BetweenLineAndCircle(     Vector2 circleCenter, float circleRadius,     Vector2 point1, Vector2 point2,     out Vector2 intersection1, out Vector2 intersection2)    {        float t;        var dx = point2.x - point1.x;        var dy = point2.y - point1.y;        var a = dx * dx + dy * dy;        var b = 2 * (dx * (point1.x - circleCenter.x) + dy * (point1.y - circleCenter.y));        var c = (point1.x - circleCenter.x) * (point1.x - circleCenter.x) + (point1.y - circleCenter.y) * (point1.y - circleCenter.y) - circleRadius * circleRadius;        var determinate = b * b - 4 * a * c;        if ((a <= 0.0000001) || (determinate < -0.0000001))        {            // No real solutions.            intersection1 = Vector2.zero;            intersection2 = Vector2.zero;            return 0;        }        if (determinate < 0.0000001 && determinate > -0.0000001)        {            // One solution.            t = -b / (2 * a);            intersection1 = new Vector2(point1.x + t * dx, point1.y + t * dy);            intersection2 = Vector2.zero;            return 1;        }        // Two solutions.        t = (float)((-b + Mathf.Sqrt(determinate)) / (2 * a));        intersection1 = new Vector2(point1.x + t * dx, point1.y + t * dy);        t = (float)((-b - Mathf.Sqrt(determinate)) / (2 * a));        intersection2 = new Vector2(point1.x + t * dx, point1.y + t * dy);        return 2;    }}