unity 使用 grabpass

grabpass 功能可以方便的截取当前屏幕画面
可以很方便的实现半透明 / 折射 / 扭曲 等效果

Shader "Unlit/Grab"
{
    Properties
    {
        _MainColor ("MainColor", Color) = (1,1,1,1)
        _MainTex ("Texture", 2D) = "white" {}
        _BumpMap ("BumpMap", 2D) = "white" {}

        _SpecularColor ("SpecularColor", Color) = (1,1,1,1)
        _Gloss ("Gloss", float) = 1

        _Fresnel ("Fresnel", float) = 1
        _Distortion ("Distortion", Range(-1, 1)) = 1
        _Opacity ("Opaticy", Range(0, 1)) = 1
    }
    SubShader
    {
        Tags { "RenderType"="Transparent" "Queue"="Transparent"}
        LOD 100

        GrabPass { "_SceneTex" }

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #pragma target 3.0

            #include "UnityCG.cginc"
            #include "AutoLight.cginc"
            #include "Lighting.cginc"

            struct a2v
            {
                float4 vertex : POSITION;
                float3 normal : NORMAL;
                float4 tangent : TANGENT;
                float2 uv : TEXCOORD0;
            };

            struct v2f
            {
                float4 pos : SV_POSITION;
                float2 uv : TEXCOORD0;
                float4 grabPos : TEXCOORD1;

                float4 TtoW0 : TEXCOORD2;
                float4 TtoW1 : TEXCOORD3;
                float4 TtoW2 : TEXCOORD4;
            };

            float4 _MainColor;

            sampler2D _MainTex;
            float4 _MainTex_ST;
            sampler2D _BumpMap;
            float4 _BumpMap_ST;
            sampler2D _SceneTex;

            float4 _SpecularColor;
            float _Gloss;

            float _Distortion;
            float _Fresnel;
            float _Opacity;

            v2f vert (a2v v)
            {
                v2f o;
                o.pos = UnityObjectToClipPos(v.vertex);
                o.uv = TRANSFORM_TEX(v.uv, _MainTex);
                o.grabPos = ComputeGrabScreenPos(o.pos);

                float3 worldPos = mul(unity_ObjectToWorld, v.vertex);

                float3 worldNormal = UnityObjectToWorldNormal(v.normal);
                float3 worldTangent = UnityObjectToWorldDir(v.tangent);
                float3 worldBinormal = cross(worldNormal, worldTangent) * v.tangent.w;

                o.TtoW0 = float4(worldTangent.x, worldBinormal.x, worldNormal.x, worldPos.x);
                o.TtoW1 = float4(worldTangent.y, worldBinormal.y, worldNormal.y, worldPos.y);
                o.TtoW2 = float4(worldTangent.z, worldBinormal.z, worldNormal.z, worldPos.z);

                return o;
            }

            float4 frag (v2f i) : SV_Target
            {
                float3 worldPos = float3(i.TtoW0.w, i.TtoW1.w, i.TtoW2.w);
                float3 N = normalize(float3(i.TtoW0.z, i.TtoW1.z, i.TtoW2.z));
                float3 V = normalize(UnityWorldSpaceViewDir(worldPos));
                float3 L = _WorldSpaceLightPos0.xyz;

                float3 bumpMap = UnpackNormal(tex2D(_BumpMap, i.uv));
                bumpMap.xy *= _Distortion;
                bumpMap.z = sqrt(1.0 - saturate(dot(bumpMap.xy, bumpMap.xy)));
                float3 bumpNormal = normalize(half3(dot(i.TtoW0.xyz, bumpMap), dot(i.TtoW1.xyz, bumpMap), dot(i.TtoW2.xyz, bumpMap)));
                
                float2 sceneUV = (i.grabPos.xy / i.grabPos.w);
                sceneUV += bumpMap.rg;
                fixed4 sceneColor = tex2D(_SceneTex, sceneUV).rgb;

                float NdotL = saturate(dot(bumpNormal, L));
                float3 H = normalize(V + L);
                float HdotL = saturate(dot(bumpNormal, H));
                float NdotV = saturate(dot(bumpNormal, V));

                float3 specular = _SpecularColor.rgb * pow(HdotL, _Gloss);
                float fresnel = _Fresnel + (1 - _Fresnel) * pow(1 - NdotV, 5);

                float4 mainColor = tex2D(_MainTex, i.uv) * _MainColor;
                float3 emissiveColor = mainColor.rgb * fresnel + specular;
                float3 finalColor = lerp(sceneColor, emissiveColor, _Opacity);

                return float4(finalColor, 1);
            }
            ENDCG
        }
    }
}

水面折射

冰冻

虽然使用起来很方便，但是效率不高

还有一点就是在 urp 渲染管线下不能使用
学习了下可以替换的方式

最简单的是直接使用 shadergraph 中的 scenecolor 节点，就可以获得类似的效果，不过 scenecolor 节点是在渲染半透明物体之前，所以不能渲染半透明物体

scenecolor

还可以使用 renderer feature，主要参考这个地址 renderer feature（里面有很详细的代码和截图，所以这里就省略了）