Disable Frustum Culling?

I've come up with a partial solution. It's not perfect, but it's a lot better than it used to be.

In my camera script, at the end of the LateUpdate() method, I added this:

camera.fieldOfView = 60;
Shader.SetGlobalMatrix("viewMatrix", camera.worldToCameraMatrix);
Shader.SetGlobalMatrix("projMatrix", camera.projectionMatrix);
camera.fieldOfView = 179;

As you can see, it sets the field of view to the standard 60 degrees, sets the shader View and Projection matrices, and then forces the field of view to 179 degrees (the maximum). So, from the shader's point of view, the camera is normal, but in Unity's point of view, the frustum is widened out to the extreme. This means that when Unity does the culling and determines which objects to render, a lot more objects pass the test.

Of course, this means that you have to change your shaders to use your own matrix variables instead of the Unity built-in variables, but that's not too bad:

o.pos = mul(_Object2World, v.vertex);
o.pos = mul(viewMatrix, o.pos);
o.pos = mul(projMatrix, o.pos);

As I said, it's not perfect and some of the displaced meshes still are clipped, but it's only about 1% of the time now as opposed to about 90% of the time before.

I have also had issues with the frustum culling taking place too early / incorrectly. When using the exact same code, the frustum would cull early if the Initialization of the GameObject took place in my Update() call rather than Start(). Very strange. I changed the bounds size to be extremely large and less culling occurred, but it was still bad. When I moved the bounds center to the center of the frustum, it worked every time. To move the frustum I placed the following code at the end of my Update() - after the mesh modification:

Transform camTransform = Camera.main.transform;
float distToCenter = (Camera.main.farClipPlane - Camera.main.nearClipPlane) / 2.0f;
Vector3 center = camTransform.position + camTransform.forward * distToCenter;
float extremeBound = 500.0f;
MeshFilter meshFilter = frontRenderer.GetComponent<MeshFilter>();
meshFilter.sharedMesh.bounds = new Bounds (center, new Vector3.one * extremeBound);

Obviously if you need the bounds for anything else you'll run into problems and will want to make a backup before you force the change.

Use RecalculateBounds() after you assign the mesh to a MeshFilter component. So for example in C#:

GetComponent().mesh = aMeshObject; aMeshObject.RecalculateBounds();

This way it will recalculate renderer bounds.