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;}
}