Unity 向量和圆的交点 相交

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;
    public float crossRadius = 0.5f;//交点圆圈大小

    void OnDrawGizmos() {
        if (a == null || b == null || circleCenter == null)
            return;

        //交点1
        var intersect1 = default(Vector2);
        //交点2
        var intersect2 = default(Vector2);
        var intersectCount = BetweenLineAndCircle(circleCenter.position, radius, a.position, b.position, out intersect1, out intersect2);

        if (intersectCount > 0)
            Gizmos.DrawWireSphere(intersect1, crossRadius);

        if (intersectCount > 1)
            Gizmos.DrawWireSphere(intersect2, crossRadius);

        Gizmos.DrawLine(a.position, b.position);
        Gizmos.DrawWireSphere(circleCenter.position, radius);
    }

    /// <summary>
    ///
    /// </summary>
    /// <param name="circleCenter"></param>
    /// <param name="circleRadius"></param>
    /// <param name="point1"></param>
    /// <param name="point2"></param>
    /// <param name="intersection1">交点1</param>
    /// <param name="intersection2">交点2</param>
    /// <returns></returns>
    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)) {
            //没有交点的情况
            intersection1 = Vector2.zero;
            intersection2 = Vector2.zero;
            return 0;
        }

        if (determinate < 0.0000001 && determinate > -0.0000001) {
            //一个交点的情况
            t = -b / (2 * a);
            intersection1 = new Vector2(point1.x + t * dx, point1.y + t * dy);
            intersection2 = Vector2.zero;
            return 1;
        }

        //两个交点的情况
        t = ((-b + Mathf.Sqrt(determinate)) / (2 * a));
        intersection1 = new Vector2(point1.x + t * dx, point1.y + t * dy);
        t = ((-b - Mathf.Sqrt(determinate)) / (2 * a));
        intersection2 = new Vector2(point1.x + t * dx, point1.y + t * dy);

        return 2;
    }
}