主要介绍AABB碰撞检测下，矩形该如何和矩形进行碰撞检测/和圆形进行碰撞检测。
直接看图，主要是比较两个矩形的边界线的前后关系。

效果

分析什么时候重合

分析什么时候不重合

完整代码

矩形身上挂载

public class Rectangle : MonoBehaviour
{
    public float width;
    public float heigth;
    private Color showColor;
    public Vector3 leftDownpoint { get; private set; }
    public Vector3 rightUppoint { get; private set; }
    private Vector3 leftUppoint;
    private Vector3 rightDownpoint;
    // Start is called before the first frame update
    void Start()
    {
        showColor = Color.green;
        RectangleCollisonManager.GetInstance().RegistCollider(this);       
    }
    public void Detect(Vector3 leftDownPoint, Vector3 rightUpPoint)
    {
        if(this.rightUppoint.x < leftDownPoint.x || rightUpPoint.x < this.leftDownpoint.x || this.rightUppoint.y < leftDownPoint.y || rightUpPoint.y < this.leftDownpoint.y)
        {
            showColor = Color.green;
            return;
        }
        showColor = Color.red;
    }
    // Update is called once per frame
    void Update()
    {
        leftDownpoint = transform.position;
        leftUppoint = transform.position + transform.up * heigth;
        rightDownpoint = transform.position + transform.right * width;
        rightUppoint = transform.position + transform.right * width + transform.up * heigth;
        DrawRectangle();
    }

    void DrawRectangle()
    {
        Debug.DrawLine(leftDownpoint, leftUppoint, showColor);
        Debug.DrawLine(leftDownpoint, rightDownpoint, showColor);
        Debug.DrawLine(leftUppoint, rightUppoint, showColor);
        Debug.DrawLine(rightUppoint, rightDownpoint, showColor);
    }
}

负责让所有矩形互相进行检测

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

public class RectangleCollisonManager : BaseManager<RectangleCollisonManager>
{
    private List<Rectangle> RectangleCollider;
    public void Init()
    {
    }

    public void RegistCollider(Rectangle r)
    {
        if(RectangleCollider == null)
        {
            RectangleCollider = new List<Rectangle>();
        }
        RectangleCollider.Add(r);
    }

    public void Update()
    {
        DetectCollision();
    }
    void DetectCollision()
    {
        for (int i = 0; i < RectangleCollider.Count; i++)
        {
            for(int j = 0 ; j < RectangleCollider.Count; j++)
            {
                if (j != i)
                {
                    RectangleCollider[i].Detect(RectangleCollider[j].leftDownpoint, RectangleCollider[j].rightUppoint);
                }
            }
        }
    }
}

tickManger调用管理器的tick，挂载在场景任意物体上面

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

public class TickManager : MonoBehaviour
{
    private RectangleCollisonManager m_rectangleCollisonManager;
    // Start is called before the first frame update
    void Start()
    {
        m_rectangleCollisonManager = RectangleCollisonManager.GetInstance();
        m_rectangleCollisonManager.Init();
    }

    // Update is called once per frame
    void Update()
    {
        m_rectangleCollisonManager.Update();
    }
}

单例基类

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

public class BaseManager<T> where T : new()
{
    private static T instance;
    public static T GetInstance()
    {
        if (instance == null)
        {
            instance = new T();
            return instance;
        }
        else
        {
            return instance;
        }
    }
}