Question about bounds.extents and how it is used

Unity Engine
1

Hi there

I’m trying to learn about Bounds.extents at the moment and I’m having trouble trying to understand what extents are and how they are used. I know that extents are described as “the extents of the Bounding Box which is always half the size of the bounds.” I got that description from looking at the following link: Unity - Scripting API: Bounds.extents

I don’t know what this means in layman’s terms?

In order to try to understand what extents actually are I wrote the following code in a script that is attached to a quad that has a BoxCollider2D attached to it as shown here:

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

public class Player : MonoBehaviour
{

      Collider2D _collider2D;
    public Vector2 _myScale;
    // Start is called before the first frame update
    void Start()
    {
        _collider2D = gameObject.GetComponent<Collider2D>();
        //Output the GameObject's Collider Bound extents
      
    }

    // Update is called once per frame
    void Update()
    {
        Debug.Log("extents : " + _collider2D.bounds.extents);
    }
}

So when I run the code I get the extents of the Bounding Box outputted to the console. The output seems to be presented in X,Y and Z co-ordinates. If I use the “Rect Tool” while in scene view when this code is running and drag the right side of the quad towards the right the X value of the extents changes along with the X value in Scale within the Transform component of the Quad.

So are extents similar in nature to the Scale values of the Transform component? The X and Y values of the extents of the Bounding Box are basically the lengths of units that the Bounding Box occupies in world space? Would this diagram that I’ve created be correct?: Bounds-Extents hosted at ImgBB — ImgBB

2

extents is a Vector that is related to the “size” of the bounding box. You can think of it as a arrow that goes from the center of the bounding box to the “maximum” corner of the box. Here’s a 2D representation:

7003400--827864--upload_2021-4-3_12-10-24.png
The x and y components of extents are half of the width and half of the height of the box, respectively (and z is half of the “depth”).

You can think of it as the “wingspan” of the bounding box, or how far the box “extends” from its center point in each dimension.

9 Likes
3

A use case that I’ve seen is for infinite scrolling background with “leapfrogging” sprites. By using bounds.extents you don’t have to hardcode when to leapfrog, no matter the sprite’s width.