OnPreCull is called before a camera culls the scene.

Culling determines which objects are visible to the camera. OnPreCull is called just before this process. This message is sent to all scripts attached to the camera.

If you want to change camera's viewing parameters (e.g. fieldOfView or just transform), this is the place to do it. Visibility of scene objects will be determined based on camera's parameters after OnPreCull.

	// Attach this to a camera.
	// Inverts the vie of the camera so everything rendered by it, is flipped
	// This will only work on  Unity - PRO
	
	function OnPreCull () {
		camera.ResetWorldToCameraMatrix ();
		camera.ResetProjectionMatrix ();
		camera.projectionMatrix = camera.projectionMatrix * Matrix4x4.Scale(Vector3 (1, -1, 1));
	}
	// Set it to true so we can watch the flipped Objects
	function OnPreRender () {
		GL.SetRevertBackfacing (true);
	}
	
	// Set it to false again because we dont want to affect all other cammeras.
	function OnPostRender () {
		GL.SetRevertBackfacing (false);
	}

using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    void OnPreCull() {
        camera.ResetWorldToCameraMatrix();
        camera.ResetProjectionMatrix();
        camera.projectionMatrix = camera.projectionMatrix * Matrix4x4.Scale(new Vector3(1, -1, 1));
    }
    void OnPreRender() {
        GL.SetRevertBackfacing(true);
    }
    void OnPostRender() {
        GL.SetRevertBackfacing(false);
    }
}

import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	def OnPreCull() as void:
		camera.ResetWorldToCameraMatrix()
		camera.ResetProjectionMatrix()
		camera.projectionMatrix = (camera.projectionMatrix * Matrix4x4.Scale(Vector3(1, -1, 1)))

	def OnPreRender() as void:
		GL.SetRevertBackfacing(true)

	def OnPostRender() as void:
		GL.SetRevertBackfacing(false)