PostEffect - Hole

using UnityEngine;
using System.Collections;

[RequireComponent(typeof(Camera))]
public abstract class CustomImageEffect : MonoBehaviour
{
    #region Fields

    private Material m_Material;

    #endregion

    #region Properties

    public abstract string ShaderName { get; }
    protected Material Material { get { return m_Material; } }

    #endregion

    #region Messages

    protected virtual void Awake()
    {
        Shader shader = Shader.Find(ShaderName);
        if (shader != null)
        {
            m_Material = new Material(shader);
            m_Material.hideFlags = HideFlags.HideAndDontSave;
        }
    }

    void Start()
    {
        if (!SystemInfo.supportsImageEffects)
        {
            enabled = false;
            return;
        }

        if (!m_Material && !m_Material.shader.isSupported)
        {
            enabled = false;
        }
    }

    protected virtual void OnRenderImage(RenderTexture source, RenderTexture destination)
    {
        if (m_Material != null)
        {
            UpdateMaterial();
            Graphics.Blit(source, destination, m_Material);
        }
        else
        {
            Graphics.Blit(source, destination);
        }
    }

    #endregion

    #region Methods

    protected abstract void UpdateMaterial();

    #endregion
}

using UnityEngine;
using System.Collections;

[ExecuteInEditMode]
public class HoleImageEffect : CustomImageEffect
{
    #region Fields

    [SerializeField]
    private Vector2 m_Center;

    [SerializeField]
    [Range(100, 2000)]
    private float m_Size;

    [SerializeField]
    [Range(0, 1)]
    private float m_Time;

    #endregion

    #region Properties

    public override string ShaderName
    {
        get { return "Custom/Hole"; }
    }

    #endregion

    #region Methods

    protected override void UpdateMaterial()
    {
        Material.SetVector("_Center", m_Center);
        Material.SetFloat("_Size", m_Size);
        Material.SetFloat("_AnimTime", m_Time);
    }
    #endregion
}

Shader "Custom/Hole" {
    Properties {
        _MainTex ("Source", 2D) = "white" {}
        _Center ("Center", Vector) = (0,0,0,0)
        _Size ("Size", Float) = 1
        _AnimTime ("Animation Time", Range(0,1)) = 0
    }
    SubShader {
        ZTest Always
        Cull Off
        ZWrite Off
        Fog { Mode Off }

        Pass{
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            
            #include "UnityCG.cginc"

            struct v2f {
                float4 pos : SV_POSITION;
                float2 uv : TEXCOORD0;
            };

            v2f vert(appdata_img v) {
                v2f o;
                o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
                o.uv = MultiplyUV(UNITY_MATRIX_TEXTURE0, v.texcoord.xy);
                return o;
            }

            sampler2D _MainTex;
            float2 _Center;
            float _Size;
            float _AnimTime;

            fixed4 frag(v2f i) : SV_TARGET {
                float d = distance(_Center, i.uv * _ScreenParams.xy);
                float visible = 1.0 - floor(d / _Size + _AnimTime);
                return fixed4(tex2D(_MainTex, i.uv).rgb * visible, 1.0);
            }
            ENDCG
        }
    }
    FallBack Off
}