Question Shader math to cull part of mesh

Hello,

I am trying to refresh my math knowledge since I have not done my vectors for a while and have run into trouble trying to make this shader work.

What I would like to do is create a material (shader) that culls part of a mesh (think of it as if you are pulling something out of a portal and it is slowly appearing on one side of it). A plane (any location, any orientation) can be placed over an object and it will clip one side of the mesh.

However, as I have it now, nothing is happening... the shader gets applied to a cube and there is an intersecting plane, but everything is still being rendered. Does anyone have an idea as to where I am going wrong with this shader to achieve the effect I am looking for? I remember finding a similar shader (regular HLSL) but I wanted to try and make it with shadergraph, resulting in a few headaches... I assume my vector logic is wrong, but I can't seem to find the solution.

The Shadergraph is as follows:

It has a script attached to it like this:

Code (CSharp):

1. using UnityEngine;
2.  
3. [ExecuteInEditMode]
4. public class PortalPullProperties : MonoBehaviour
5. {
6.     [SerializeField] private GameObject _clippingPlane = null;
7.     [SerializeField] private Vector3 _rotationOffset = new Vector3(0, 90, 0);
8.  
9.     private Material _material = null;
10.     private MeshRenderer _renderer = null;
11.  
12.     public GameObject ClippingPlane { get => _clippingPlane; }
13.  
14.     private void Start()
15.     {
16.         _renderer = gameObject.GetComponent<MeshRenderer>();
17.         _material = _renderer.sharedMaterial;
18.     }
19.  
20.     void Update()
21.     {
22.         if((_clippingPlane && _clippingPlane.transform.hasChanged) || transform.hasChanged)
23.         {
24.             Vector3 position = _clippingPlane.transform.position;
25.             Vector3 rotation = _clippingPlane.transform.forward + _rotationOffset;
26.  
27.             _material.SetVector("_ClippingPlanePosition", new Vector4(position.x, position.y, position.z));
28.             _material.SetVector("_ClippingPlaneOrientation", new Vector4(rotation.x, rotation.y, rotation.z));
29.         }
30.     }
31.  
32.     private void Reset()
33.     {
34.         this.GetComponent<MeshRenderer>().material = new Material(Shader.Find("Shader Graphs/PortalPull"));
35.     }
36. }

 

Your math looks right, you should just need to plug your dot product result straight into the Master node's Alpha input. Alpha Clip Threshold would then be 0 to cull everything behind your plane.

 

Seems like that was not the only thing going wrong with my shader. The result looks like this. Which is still not doing anything sadly... I wonder what is going wrong, given that you are telling me my math is correct I am pretty much at a loss.