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前言

我们在这篇文章中看一下，URP下怎么开启抓屏。

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一、抓屏开启

1、Unity下开启抓屏

• 在URP下，打开下面这个选项
  
• Frame Debugger下可以看见 CopyColor 就是我们上一帧的内容
  
• Opaque Downsampling改变截取的帧精度
  

2、Shader中开启抓屏

• 使用不透明渲染队列才可以使用深度图
• Render Queue < 2500 时才可以使用深度图
  

Tags{“Queue”=“Geometry}”

• 开启Zwrite

Zwrite On

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二、抓屏使用

• 我们这里创建一个面片来测试一下

1、设置为半透明渲染队列，关闭深度写入

• 因为，要用面片显示抓取的内容。
• 所以，我们得让抓屏不把该面片抓进去，需要抓取的其他物体开启抓屏。

Tags{“Queue”=“Transparent”}

ZWrite Off

2、申明纹理和采样器

TEXTURE2D(_CameraOpaqueTexture);SAMPLER(sampler_CameraOpaqueTexture);

• 也可以直接使用hlsl内部定义

#define REQUIRE_OPAQUE_TEXTURE

3、在片元着色器使用

• 使用模型uv采样

float4 opaqueMap = SAMPLE_TEXTURE2D(_CameraOpaqueTexture,sampler_CameraOpaqueTexture,i.uv);
return opaqueMap;

• 使用屏幕uv采样（为了使其效果明显，我们给输出结果加上0.3)

float2 uv = i.positionCS.xy/ _ScreenParams.xy;
float4 opaqueMap = SAMPLE_TEXTURE2D(_CameraOpaqueTexture,sampler_CameraOpaqueTexture,uv);
return opaqueMap+0.3;

三、测试代码

Shader "MyShader/URP/P4_2"
{
    Properties 
    {
        _Color("Color",Color) = (0,0,0,0)
        _MainTex("MainTex",2D) = "white"{}
    }
    SubShader
    {
        Tags
        {
            //告诉引擎，该Shader只用于 URP 渲染管线
            "RenderPipeline"="UniversalPipeline"
            //渲染类型
            "RenderType"="Transparent"
            //渲染队列
            "Queue"="Transparent"
        }
        //Blend One One
        ZWrite Off
        Pass
        {
            Name "Unlit"
          
            HLSLPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            // Pragmas
            #pragma target 2.0
            
            // Includes
            #include "Packages/com.unity.render-pipelines.core/ShaderLibrary/Color.hlsl"
            #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"
            #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Input.hlsl"

            CBUFFER_START(UnityPerMaterial)
            half4 _Color;
            CBUFFER_END

            
            //纹理的定义，如果是编译到GLES2.0平台，则相当于sample2D _MainTex;否则相当于 Texture2D _MainTex;
            TEXTURE2D(_MainTex);SAMPLER(SamplerState_linear_mirrorU_ClampV); float4 _MainTex_ST;
            TEXTURE2D(_CameraDepthTexture);SAMPLER(sampler_CameraDepthTexture);
            TEXTURE2D(_CameraOpaqueTexture);SAMPLER(sampler_CameraOpaqueTexture);
            
            //struct appdata
            //顶点着色器的输入
            struct Attributes
            {
                float3 positionOS : POSITION;
                float2 uv : TEXCOORD0;
            };
            //struct v2f
            //片元着色器的输入
            struct Varyings
            {
                float4 positionCS : SV_POSITION;
                float2 uv : TEXCOORD0;
                float4 screenPos : TEXCOORD1;
            };
            //v2f vert(Attributes v)
            //顶点着色器
            Varyings vert(Attributes v)
            {
                Varyings o = (Varyings)0;
                float3 positionWS = TransformObjectToWorld(v.positionOS);
                o.positionCS = TransformWorldToHClip(positionWS);
                o.uv = TRANSFORM_TEX(v.uv,_MainTex);
                o.screenPos = ComputeScreenPos(o.positionCS);
                return o;
            }
            //fixed4 frag(v2f i) : SV_TARGET
            //片元着色器
            half4 frag(Varyings i) : SV_TARGET
            {
                half4 c;
                
                float4 mainTex = SAMPLE_TEXTURE2D(_MainTex,SamplerState_linear_mirrorU_ClampV,i.uv);
                //c = _Color *  mainTex;
                //深度图
                //float2 uv = i.screenPos.xy / i.screenPos.w;
                //float2 uv = i.positionCS.xy/ _ScreenParams.xy;
                //float4 cameraDepthTex = SAMPLE_TEXTURE2D(_CameraDepthTexture,sampler_CameraDepthTexture,uv);
                //float depthTex = Linear01Depth(cameraDepthTex,_ZBufferParams);
                //抓屏
                float2 uv = i.positionCS.xy/ _ScreenParams.xy;
                float4 opaqueMap = SAMPLE_TEXTURE2D(_CameraOpaqueTexture,sampler_CameraOpaqueTexture,uv);
                return opaqueMap;
            }
            ENDHLSL
        }
    }

    SubShader
    {
        Tags
        {
            //渲染类型
            "RenderType"="Transparent"
            //渲染队列
            "Queue"="Transparent"
        }
        //Blend One One
        ZWrite Off
        Pass
        {
           
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            // Pragmas
            #pragma target 2.0
            
            // Includes
            #include "UnityCG.cginc"
            
           
            half4 _Color;
            sampler2D _MainTex;float4 _MainTex_ST;
            sampler2D _CameraDepthTexture;
            
            
            struct appdata
            {
                float3 positionOS : POSITION;
                float2 uv : TEXCOORD0;
            };
            
            struct v2f
            {
                float4 positionCS : SV_POSITION;
                float2 uv : TEXCOORD0;
                float4 screenPos : TEXCOORD1;
            };
          
            v2f vert(appdata v)
            {
                v2f o;
                o.positionCS = UnityObjectToClipPos(v.positionOS);
                o.uv = TRANSFORM_TEX(v.uv,_MainTex);
                o.screenPos = ComputeScreenPos(o.positionCS);
                return o;
            }
            //fixed4 frag(v2f i) : SV_TARGET
            //片元着色器
            half4 frag(v2f i) : SV_TARGET
            {
                half4 c;
                
                float4 mainTex = tex2D(_MainTex,i.uv);
                //c = _Color *  mainTex;
                //深度图
                //float2 uv = i.screenPos.xy / i.screenPos.w;
                float2 uv = i.positionCS/ _ScreenParams.xy;
                float4 cameraDepthTex = tex2D(_CameraDepthTexture,uv);
                float depthTex = Linear01Depth(cameraDepthTex);
                return depthTex;
            }
            ENDCG
        }
    }
}