MonoBehaviour.OnWillRenderObject()

Description

OnWillRenderObject is called for each camera if the object is visible and not a UI element.

The function is not called if the MonoBehaviour is disabled.

The function is called during the culling process just before rendering each culled object.

Note that Camera.current will be set to the camera that will render the object.

Note: This has no effect when called from a UI element.

using UnityEngine;
using System.Collections;

public class ExampleScript : MonoBehaviour
{
    public Renderer rend;

    private float timePass = 0.0f;

    void Start()
    {
        rend = GetComponent<Renderer>();
    }

    void OnWillRenderObject()
    {
        timePass += Time.deltaTime;

        if (timePass > 1.0f)
        {
            timePass = 0.0f;
            print(gameObject.name + " is being rendered by " + Camera.current.name + " at " + Time.time);
        }
    }
}

This is called multiple times per frame.