# 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;

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)

if (intersectCount > 1)

Gizmos.DrawLine(a.position, b.position);
}

/// <summary>
///
/// </summary>
/// <param name="circleCenter"></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;
}
}

posted @ 2022-01-14 15:06  三页菌  阅读(118)  评论(0编辑  收藏  举报