2D空间中求线段与圆的交点

出处: https://answers.unity.com/questions/366802/get-intersection-of-a-line-and-a-circle.html

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 > )

            Gizmos.DrawWireSphere(intersect1, 0.1f);

        if (intersectCount > )

            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 =  * (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 -  * a * c;

        if ((a <= 0.0000001) || (determinate < -0.0000001))

        {

            // No real solutions.

            intersection1 = Vector2.zero;

            intersection2 = Vector2.zero;

            return ;

        }

        if (determinate < 0.0000001 && determinate > -0.0000001)

        {

            // One solution.

            t = -b / ( * a);

            intersection1 = new Vector2(point1.x + t * dx, point1.y + t * dy);

            intersection2 = Vector2.zero;

            return ;

        }

        // Two solutions.

        t = (float)((-b + Mathf.Sqrt(determinate)) / ( * a));

        intersection1 = new Vector2(point1.x + t * dx, point1.y + t * dy);

        t = (float)((-b - Mathf.Sqrt(determinate)) / ( * a));

        intersection2 = new Vector2(point1.x + t * dx, point1.y + t * dy);

        return ;

    }

}