円の外接三角形の頂点計算

ceternalTriangle.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Test : MonoBehaviour
{
	[SerializeField]
	private float _radius = 1f;

	private Vector3 _center = Vector3.zero;

	private Vector3 _A, _B, _C;

	private void Start()
	{
		Calc();
	}

	private void Calc()
	{
		float cx = _center.x;
		float cy = _center.z;
		float r = _radius;
		float r2 = r * 2f;
		float r3 = r * Mathf.Sqrt(3f);

		float Ax = (cx - r2);
		float Ay = (cy - r);
		float Bx = (cx + r2);
		float By = (cy - r);
		float Cx = cx;
		float Cy = (cy + r3);

		_A = new Vector3(Ax, 0, Ay);
		_B = new Vector3(Bx, 0, By);
		_C = new Vector3(Cx, 0, Cy);
	}
	
	private void OnDrawGizmos()
	{
		if (!Application.isPlaying)
		{
			return;
		}

		UnityEditor.Handles.DrawWireDisc(_center, Vector3.up, _radius);

		Gizmos.color = Color.red;
		Gizmos.DrawLine(_A, _B);
		Gizmos.DrawLine(_B, _C);
		Gizmos.DrawLine(_C, _A);

		Gizmos.color = Color.cyan;
		Gizmos.DrawWireSphere(_center, 0.1f);
	}
}