Drawing camera frustum with a mesh, strange behaviour

Hi

I need to create a mesh representing the frustum of a camera. I almost have it !!! But somehow there is a problem when i move this camera: the mesh is not following it properly.

As you can see, i am also drawing the frustum with some "Debug.DrawLine", feeding them the exact same point as my mesh, and it's displaying properly.

What am i missing ??

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class DrawCamFov : MonoBehaviour {
6.  
7.     public Camera cam;
8.  
9.     GameObject[] Triangles;
10.  
11.     private void Start()
12.     {
13.         Triangles = new GameObject[4];
14.         for (int i = 0; i < 4; i++)
15.         {
16.             GameObject child = new GameObject();
17.             MeshFilter mf = child.AddComponent<MeshFilter>();
18.             child.transform.parent = cam.transform;
19.             Triangles[i] = child;
20.  
21.             Vector3[] vertices = new Vector3[]
22.             {
23.                 Vector3.zero,
24.                 Vector3.zero,
25.                 Vector3.zero
26.             };
27.             int[] triangles = new int[]
28.             {
29.              2,1,0
30.             };
31.  
32.             mf.mesh = new Mesh();
33.             mf.mesh.vertices = vertices;
34.             mf.mesh.triangles = triangles;
35.  
36.             child.AddComponent<MeshRenderer>();
37.         }
38.     }
39.  
40.     void Update()
41.     {
42.         DrawFrustum(cam);
43.     }
44.  
45.     void DrawFrustum(Camera cam)
46.     {
47.         Vector3[] nearCorners = new Vector3[4]; //Approx'd nearplane corners
48.         Vector3[] farCorners = new Vector3[4]; //Approx'd farplane corners
49.         Plane[] camPlanes = GeometryUtility.CalculateFrustumPlanes(cam); //get planes from matrix
50.  
51.         Plane temp = camPlanes[1]; camPlanes[1] = camPlanes[2]; camPlanes[2] = temp; //swap [1] and [2] so the order is better for the loop
52.         for (int i = 0; i < 4; i++)
53.         {
54.             nearCorners[i] = Plane3Intersect(camPlanes[4], camPlanes[i], camPlanes[(i + 1) % 4]); //near corners on the created projection matrix
55.             farCorners[i] = Plane3Intersect(camPlanes[5], camPlanes[i], camPlanes[(i + 1) % 4]); //far corners on the created projection matrix
56.         }
57.  
58.         for (int i = 0; i < 4; i++)
59.         {
60.             Debug.DrawLine(nearCorners[i], nearCorners[(i + 1) % 4], Color.red, Time.deltaTime, true); //near corners on the created projection matrix
61.             Debug.DrawLine(farCorners[i], farCorners[(i + 1) % 4], Color.blue, Time.deltaTime, true); //far corners on the created projection matrix
62.             Debug.DrawLine(nearCorners[i], farCorners[i], Color.green, Time.deltaTime, true); //sides of the created projection matrix
63.  
64.  
65.             Triangles[i].GetComponent<MeshFilter>().mesh.vertices = new[]
66.              {
67.                      transform.position,
68.                      farCorners[i],
69.                      farCorners[(i + 1) % 4]
70.              };
71.         }
72.     }
73.  
74.     Vector3 Plane3Intersect(Plane p1, Plane p2, Plane p3)
75.     { //get the intersection point of 3 planes
76.         return ((-p1.distance * Vector3.Cross(p2.normal, p3.normal)) +
77.                 (-p2.distance * Vector3.Cross(p3.normal, p1.normal)) +
78.                 (-p3.distance * Vector3.Cross(p1.normal, p2.normal))) /
79.          (Vector3.Dot(p1.normal, Vector3.Cross(p2.normal, p3.normal)));
80.     }
81. }
82.  

All the credit for the "working part" of this code should be given to my inspiration source :
https://grrava.blogspot.com/2014/04/render-view-frustrum-of-camera-in-unity.html

 

I'm guessing your GeometryUtility.CalculateFrustumPlanes is already pre-transforming the coordinates, then you're making the thing a child of the camera itself, so when it turns, it essentially "double turns."

Relative to the camera's transform, for a given frustum the points will be static, i.e., relative to it.

 

Thanks for the quick reply but i'm not sure to understand how i can solve this problem. Should i divide by 2 all my points position ? It doesn't sound like a clean solution :O
I will try another approach though, using this example:
https://docs.unity3d.com/2018.3/Documentation/ScriptReference/Camera.CalculateFrustumCorners.html

 

Aaaaaaand it works perfectly

So if you want to achieve the same thing, replace this function in the previous code with :

Code (CSharp):

1. void DrawFrustum(Camera cam)
2.     {
3.         Vector3[] frustumCorners = new Vector3[4];
4.         cam.CalculateFrustumCorners(new Rect(0, 0, 1, 1), cam.farClipPlane, Camera.MonoOrStereoscopicEye.Mono, frustumCorners);
5.  
6.         for (int i = 0; i < 4; i++)
7.         {
8.             var worldSpaceCorner = cam.transform.TransformVector(frustumCorners[i]);
9.             Debug.DrawRay(cam.transform.position, worldSpaceCorner, Color.blue);
10.  
11.             Triangles[i].GetComponent<MeshFilter>().mesh.vertices = new[]
12.              {
13.                      cam.transform.position,
14.                      frustumCorners[i],
15.                      frustumCorners[(i + 1) % 4]
16.                    
17.             };
18.         }
19.     }

Cleaner, easyer, Better

 

The best lines of code are ones that you delete: they cannot possibly have a bug.

 

You may found them better, but :

Code (CSharp):

1.  Vector3[] frustumCorners = new Vector3[4];
2.         camera.CalculateFrustumCorners(new Rect(0, 0, 1, 1), camera.farClipPlane, Camera.MonoOrStereoscopicEye.Mono, frustumCorners);
3.  

works perfectly and fit in 2 lines. Plus it's directly copy and paste from unity documentation.