unity置灰处理的实现

Shader "UI/UIGray"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        [Toggle]_ShowGray("show gray", Range(0,1)) = 0
    }
    SubShader
    {
        // No culling or depth
        Cull Off ZWrite Off ZTest Always
        //-----add code-------
        Blend SrcAlpha OneMinusSrcAlpha
        //----finish----
        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag

            #include "UnityCG.cginc"

            struct appdata
            {
                float4 vertex : POSITioN;
                float2 uv : TEXCOORD0;
            };

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

            v2f vert (appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = v.uv;
                return o;
            }

            sampler2D _MainTex;
            fixed _ShowGray;

            fixed4 frag (v2f i) : SV_Target
            {
                fixed4 col = tex2D(_MainTex, i.uv);
                // just invert the colors
                //col.rgb = 1 - col.rgb;
            //----add code----
                fixed gray = dot(col.rgb, float3(0.298912, 0.586611, 0.114478));
                col.rgb = lerp(col.rgb, fixed3(gray, gray, gray), _ShowGray);
            //-----finish-----
                return col;
            }
            ENDCG
        }
    }
}

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class PostEffectGray : MonoBehaviour
{
    public Material grayMaterial;
    void OnRenderImage(RenderTexture src, RenderTexture dest)
    {
        Graphics.Blit(src, dest, grayMaterial);
    }
}

Shader "Unlit/Gray"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 100

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            // make fog work
            #pragma multi_compile_fog

            #include "UnityCG.cginc"

            struct appdata
            {
                float4 vertex : POSITION;
                float2 uv : TEXCOORD0;
            };

            struct v2f
            {
                float2 uv : TEXCOORD0;
                UNITY_FOG_COORDS(1)
                float4 vertex : SV_POSITION;
            };

            sampler2D _MainTex;
            float4 _MainTex_ST;

            v2f vert (appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = TRANSFORM_TEX(v.uv, _MainTex);
                UNITY_TRANSFER_FOG(o,o.vertex);
                return o;
            }

            fixed4 frag (v2f i) : SV_Target
            {
                // sample the texture
                fixed4 col = tex2D(_MainTex, i.uv);
                half3 gray = dot(col.rgb, half3 (0.22, 0.707, 0.071));
            // apply fog
                UNITY_APPLY_FOG(i.foGCoord, col);
                return fixed4(gray.rgb, col.a);
            }
            ENDCG
        }
    }
}