之前的面试的时候有被问到，像4月4号清明节的时候，很多软件的界面都变成灰色，想要实现这个有什么思路，当时由于紧张，没有什么思路，后面想想，用屏幕后处理是可以实现的，像很多游戏，主角死亡后，游戏画面变灰，会不会也是这么实现的呢？话不多说，直接上代码：
CS代码：
首先我要准备渲染RenderTexture的材质，这里我们使用一个可以在屏幕后处理中使用的通用基类。

using UnityEngine;
using System.Collections;

[ExecuteInEditMode]
[RequireComponent (typeof(Camera))]
public class PostEffectsBase : MonoBehaviour {
    protected void Start() {
        CheckResources();
    }
    
    protected void CheckResources() {
        bool isSupported = CheckSupport();
        
        if (isSupported == false) {
            NotSupported();
        }
    }

    // 检测设备是否支持屏幕特效和渲染纹理
    protected bool CheckSupport() {
        if (SystemInfo.supportsImageEffects == false || SystemInfo.supportsRenderTextures == false) {
            Debug.LogWarning("This platform does not support image effects or render textures.");
            return false;
        }
        
        return true;
    }

    protected void NotSupported() {
        enabled = false;
    }

    // 创建新的材质去渲染动态纹理
    protected Material CheckShaderAndCreateMaterial(Shader shader, Material material) {
        if (shader == null) {
            return null;
        }
        
        if (shader.isSupported && material && material.shader == shader)
            return material;
        
        if (!shader.isSupported) {
            return null;
        }
        else {
            material = new Material(shader);
            material.hideFlags = HideFlags.HideAndDontSave;
            if (material)
                return material;
            else 
                return null;
        }
    }
}

创建一个我们操作界面变灰的脚本，继承自PostEffectsBase，同时将该脚本挂到摄像机上。

using UnityEngine;
using System.Collections;

[ExecuteInEditMode]
public class SceneGray : PostEffectsBase
{
    //设置渲染的shader
    public Shader curShader;
    //灰度程度0~1，0为原来颜色，1为灰色
    public float grayScaleAmount = 1.0f;
    //新创建的材质
    private Material curMaterial;

    Material material
    {
        get
        {
            if (curMaterial == null)
            {
                curMaterial = CheckShaderAndCreateMaterial(curShader,curMaterial);
            }
            return curMaterial;
        }
    }
    //屏幕后处理函数，设置shader参数
    void OnRenderImage(RenderTexture sourceTexture, RenderTexture destTexture)
    {
        if (curShader != null)
        {
            material.SetFloat("_LuminosityAmount", grayScaleAmount);
            Graphics.Blit(sourceTexture, destTexture, material);
        }
        else
        {
            Graphics.Blit(sourceTexture, destTexture);
        }
    }
    //设置灰度程度
    void Update()
    {
        grayScaleAmount = Mathf.Clamp(grayScaleAmount, 0, 1.0f);
    }
    //删除新建的材质
    void OnDisable()
    {
        if (curMaterial)
        {
            DestroyImmediate(curMaterial);
        }
    }
}

shader代码：

Shader "Custom/GrayColor" {
    Properties {
        _MainTex ("Base (RGB)", 2D) = "white" {}
        _grayScale("_grayScale",Float) = 1.0
    }
    SubShader {
        Pass {  
            ZTest Always Cull Off ZWrite Off
            
            CGPROGRAM  
            #pragma vertex vert  
            #pragma fragment frag  
              
            #include "UnityCG.cginc"  
              
            sampler2D _MainTex;  
            half _grayScale;
              
            struct v2f {
                float4 pos : SV_POSITION;
                half2 uv: TEXCOORD0;
            };
              
            v2f vert(appdata_img v) {
                v2f o;
                o.pos = UnityObjectToClipPos(v.vertex);
                o.uv = v.texcoord;   
                return o;
            }
        
            fixed4 frag(v2f i) : SV_Target {
                fixed4 renderTex = tex2D(_MainTex, i.uv); 
                //置灰后的灰色值
                float gray = dot(renderTex.rgb, float3(0.299, 0.587, 0.114));
                fixed4 grayColor = fixed4(gray, gray, gray,renderTex.a);
                //将原来的颜色与灰色做插值运算
                fixed4 finalColor = lerp(renderTex,grayColor,_grayScale);
                return finalColor;
            }  
              
            ENDCG
        }  
    }
    
    Fallback Off
}

最终效果：

GrayScaleAmount=0.png

GrayScaleAmount=1.png