Frustum Cull - GeometryUtility TestPlanesAABB - False Positives

Unity Engine
1

Hi all,

I’ve recently been trying to implement a simple AABB culling system - I’m aware of the OnBecameVisible() and Renderer.isVisible functions, however what I’m trying to cull does not have a renderer component; basically, a large node so I can ‘batch-turn-off’ all the objects inside (as part of a Quadtree).

My problem is - there are certain situations where I’m getting false-positives (stuff is not being culled when it should be) and I’m at a loss to explain it. The code snippet below can recreate the problem (attach it to a simple cube or object with bounds) - the false positive I’m getting is shown in the image.

Has anyone else encountered this behaviour? Is there anything I can do about it? I have implemented my own frustum tests, however I end up with much the same result.

public class CameraCull : MonoBehaviour 
{
	[SerializeField]
	Camera m_camera = null;
	
	// Update is called once per frame
	void Update() 
	{
		this.renderer.enabled = GeometryUtility.TestPlanesAABB(GeometryUtility.CalculateFrustumPlanes(m_camera), this.collider.bounds);
	}
}

1455075--78940--$culling.png

2

Apparently these false-positives are a property of conservative algorithms; the way around this is to also do a sphere/cone check before the frustum test