Screen grab GrabPass for Shader in Unity

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Preface

Screen grab GrabPass for Shader in Unity

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1. Grab

1. Fetch instructions

Screen capture requires the use of a Pass

GrabPass{}

GrabPass{“NAME”}

2. Before using the captured screen, you need to define it like an attribute. The name _GrabTexture is defined by Unity.

sampler2D _GrabTexture;

Test code:

Shader "MyShader/P0_10_3"
{
    SubShader
    {
        Tags{"Queue" = "Transparent"}
        //屏幕抓取需要单独使用一个Pass —— GrabPass{} 里面什么都不写
        GrabPass{}
        
        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #include "UnityCG.cginc"
            
            struct v2f
            {
                float2 uv : TEXCOORD0;
            };

            //在使用抓取的屏幕前，需要像使用属性一样定义一下,_GrabTexture这个名字是Unity定义好的
            sampler2D _GrabTexture;
            //在顶点着色器的输入处，不用appdata,直接使用用到的参数，防止 SV_POSITION 重复定义
            v2f vert (
                float4 vertex : POSITION,
                out float4 pos : SV_POSITION
            )
            {
                v2f o;
                pos = UnityObjectToClipPos(vertex);
                return o;
            }

            fixed4 frag (v2f i,UNITY_VPOS_TYPE screenPos : VPOS) : SV_Target
            {
                
                fixed2 screenUV = screenPos.xy / _ScreenParams.xy;
                //对抓取的屏幕进行采样
                fixed4 grabTex = tex2D(_GrabTexture,screenUV);
                return grabTex;
            }
            ENDCG
        }
    }
}

Effect:

In order to optimize and save performance: store and render after one crawl, and then crawl next time

Use: GrabPass{"NAME"}

After using this capture, the corresponding definition name must also be replaced with NAME.

Modified code:

Shader "MyShader/P0_10_3"
{
    SubShader
    {
        Tags{"Queue" = "Transparent"}
        //屏幕抓取需要单独使用一个Pass —— GrabPass{} 里面什么都不写，或者GrabPass{"_GrabTex"}
        GrabPass{"_GrabTex"}
        
        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #include "UnityCG.cginc"
            
            struct v2f
            {
                float2 uv : TEXCOORD0;
            };

            //在使用抓取的屏幕前，需要像使用属性一样定义一下,_GrabTexture这个名字是Unity定义好的
            sampler2D _GrabTex;
            //在顶点着色器的输入处，不用appdata,直接使用用到的参数，防止 SV_POSITION 重复定义
            v2f vert (
                float4 vertex : POSITION,
                out float4 pos : SV_POSITION
            )
            {
                v2f o;
                pos = UnityObjectToClipPos(vertex);
                return o;
            }

            fixed4 frag (v2f i,UNITY_VPOS_TYPE screenPos : VPOS) : SV_Target
            {
                
                fixed2 screenUV = screenPos.xy / _ScreenParams.xy;
                //对抓取的屏幕进行采样
                fixed4 grabTex = tex2D(_GrabTex,screenUV);
                return grabTex;
            }
            ENDCG
        }
    }
}

Note: This operation consumes the performance of the mobile phone and is generally enabled only in mid-range or high-end configurations.