Confusion regarding the ray box intersection

[junior-stack]

By reading the description of function ray_intersect_box, I am not sure how I can check if the ray hits something inside a box. Based on the description of AABB tree, I assume the bounding box partitions the list of objects in the scene. In that case, I assume the bounding box will store a list of leaf objects or internal node objects(other bounding boxes) in its class field. However, after I check the BoundingBox.h, I found it only contains the max_corner and min_corner, even in the insert_box_into_box, we are just modifying the box's corner cordinate instead of storing one box into another box. So I am a little confused how I can access the bounding boxes or objects that is inside a bounding box called A. Do I loop through all the bounding boxes in the scene and compare the max and min corners with the max and min corners to check if each box is in A?

[Zhecheng-Wang]

Indeed, BoundingBox.h only contains the geometry information of the box.

You are referring to the AABBTree class that defines the basic building component of AABB. Every AABBTree node contains a left subtree and a right subtree, and is inherited from Object struct that contains a BoundingBox. See code here.

[junior-stack]

Yes, I have seen this code. So my question is we are given only the geometry information of the box in ray_intersect_box, how do we determine the AABBTree node Object in the child node of the box? I don't quite understand this logic

[Zhecheng-Wang]

For ray_intersect_box, it is just checking one ray intersecting with one (geometric) box, so it can't do what you just described. I think you are thinking about a recursive function that checks ray intersection with a box and its subtree nodes? That would be AABBTree::ray_intersect.

[junior-stack]

So if I just check the box that is passed to this function, what does the sentence in the bracket "careful: if the ray or min_t lands inside the box this could still hit something stored inside the box, so this counts as a hit" mean? I thought it also needs to check ray intersection between the box inside the box that is passed to the function and ray?

[Zhecheng-Wang]

That's referring to the case if someone is doing a ray-box intersection as if the box is a surface-only geometry (hollow inside so rays stopped inside don't "hit"). We want a ray-volumetric box intersection check. As you have seen, there is no further information that can help you deduce subtree information from the BoundingBox class.