Gizmo Exampls

MainCameraBorder

using UnityEngine;
using System.Collections;

public class Gizmo : MonoBehaviour {
    public bool ShowMainCameraBorder;

    void OnDrawGizmos() {
        if (ShowMainCameraBorder) {
            float z = GetComponent<Camera>().nearClipPlane;
            Vector3 max = GetComponent<Camera>().ViewportToWorldPoint(new Vector3(1, 1, z));
            Vector3 min = GetComponent<Camera>().ViewportToWorldPoint(new Vector3(0, 0, z));
            Debug.Log(max.z);
            Debug.Log(min.z);
            Gizmos.color = Color.yellow;
            Gizmos.DrawLine(min, new Vector3(min.x, max.y, z));
            Gizmos.DrawLine(min, new Vector3(max.x, min.y, z));
            Gizmos.DrawLine(max, new Vector3(max.x, min.y, z));
            Gizmos.DrawLine(max, new Vector3(min.x, max.y, z));
        }
    }

}