Unity內實現OBB包圍盒算法

前言

作為碰撞盒的檢測，OBB是一個常用的辦法。網上有很多文章是介紹原理的，具體可以查一下。 以下給出OBB的Unity實現版本。親測可跑。

參考 ：www.tuicool.com/articles/IN…

效果

實現

基礎：對象擁有BoxCollider控件（用作包圍盒）和MeshRenderer控件（模型）

步驟：1.更新BoxCollider 2.更新AABB

更新BoxCollider。這個只需要在編輯器中更新一下即可，不需要運行時不斷更新。

using UnityEngine;
public class UpdateBoxColliderHelp
{
    private Transform m_Transform;
    private MeshRenderer m_MeshRenderer;
    private BoxCollider m_BoxCollider;
    public UpdateBoxColliderHelp(Transform transform)
    {
        m_Transform = transform;
        m_MeshRenderer = m_Transform.GetComponent<MeshRenderer>();
        m_BoxCollider = m_Transform.GetComponent<BoxCollider>();
         UpdateBoxCollider();
    }
    public void UpdateBoxCollider()
    {
        if (m_MeshRenderer == null || m_BoxCollider == null)
        {
            Debug.Log(string.Format("對象{0}沒有指定控件，跳過。", m_Transform.name));
            return;
        }
        Vector3 position = m_Transform.position;
        Vector3 scale = m_Transform.localScale;
        Quaternion rotation = m_Transform.rotation;
        m_Transform.position = Vector3.zero;
        m_Transform.localScale = Vector3.one;
        m_Transform.rotation = new Quaternion(0,0,0,1);
        m_BoxCollider.size = m_MeshRenderer.bounds.size;
        m_BoxCollider.center = m_MeshRenderer.bounds.center;
        m_Transform.position = position;
        m_Transform.localScale = scale;
        m_Transform.rotation = rotation;
        Debug.Log(string.Format("對象{0}的BoxCollider更新完畢。", m_Transform.name));
    }
}

OBB的實現

using System;
using UnityEngine;
public class OBBRect
{
    public Transform m_Transform;
    public BoxCollider m_BoxCollider;
    private double m_Rotation;
    public Vector2 m_Extents;
    public Vector2[] m_Axiss;
    public OBBRect(Transform transform)
    {
        m_Transform = transform;
        m_BoxCollider = m_Transform.GetComponent<BoxCollider>();
        m_Axiss = new Vector2[2];
        SetExtents();
    }
    private void SetExtents()
    {
        Quaternion rotation = m_Transform.rotation;
        m_Transform.rotation = new Quaternion(0, 0, 0, 1);
        Vector3 center = m_BoxCollider.center;
        Vector3 size = m_BoxCollider.size / 2;
        Vector3 Point1 = new Vector3(center.x + size.x, center.y, center.z - size.z);
        Vector3 Point2 = new Vector3(center.x - size.x, center.y, center.z + size.z);
        Point1 = m_Transform.localToWorldMatrix.MultiplyPoint3x4(Point1);
        Point2 = m_Transform.localToWorldMatrix.MultiplyPoint3x4(Point2);
        m_Extents = new Vector2(Mathf.Abs(Point1.x - Point2.x)/2,Mathf.Abs(Point2.z - Point1.z)/2);
        m_Transform.rotation = rotation;
    }
    public float dot(Vector2 a, Vector2 b)
    {
        return Mathf.Abs(a.x * b.x + a.y * b.y);
    }
    public float getProjectionRadius(Vector2 axis)
    {
        return (m_Extents.x * dot(m_Axiss[0], axis) + m_Extents.y * dot(m_Axiss[1], axis));
    }
    public void Update()
    {
        m_Rotation = m_Transform.eulerAngles.y * Math.PI / 180;
        m_Axiss[0] = new Vector2( (float) Math.Cos(m_Rotation), -(float) Math.Sin(m_Rotation));
        m_Axiss[1] = new Vector2(-m_Axiss[0].y, m_Axiss[0].x);
    }
    public bool intersects(OBBRect other)
    {
        Update();
        other.Update();
        Vector2 distanceVector = new Vector2(m_Transform.position.x - other.m_Transform.position.x, m_Transform.position.z - other.m_Transform.position.z);
       
        Vector2[] checkObbVector2s =
        {
            m_Axiss[0],
            m_Axiss[1],
            other.m_Axiss[0],
            other.m_Axiss[1],
        };
        for (int index = 0; index < checkObbVector2s.Length; index++)
        {
            Vector2 curVector2 = checkObbVector2s[index];
            if ((getProjectionRadius(curVector2) + other.getProjectionRadius(curVector2)) <= dot(distanceVector, curVector2))
            {
                return false;
            }
        }
        return true;
    }
}

注意點

1.先更新包圍盒，所有計算（寬高這些）都是基於包圍盒的數據。

2.該算法是做到模型忽略Y軸進行檢測，需要的話可以自己補充一下。思路:多一個軸向計算。

3.計算Sin值和參考文章不一樣，這里是使用-Sin才得到正確的數值。原因我也還沒想到。。。

 

原文連接：https://juejin.cn/post/6844903857206591501