ライトマッピングとシェーダーメタパス

A GameObject must use a Material that has a Meta Pass in its Shader in order to receive or contribute to lighting calculated by the Progressive Lightmapper or Enlighten Baked or Realtime Global Illumination.

A Meta Pass is a Shader pass that provides albedo and emission values to the Global Illumination system. These values are separate from those used in real-time rendering, meaning that you can use the Meta Pass to control how a GameObject looks from the point of view of the lighting baking system without affecting its appearance at runtime.

An example of when this would be useful is if you wanted the green moss on a cliff to generate exaggerated green indirect light in your lightmaps, but you didn’t want to recolor the terrain in the real-time pass of shader.

Unity のすべてのビルトインマテリアルにはメタパスがあり、そしてスタンダードシェーダーは、メタパスが含まれています。これらを使用している場合は、メタパスを有効にするために何もする必要はありません。カスタムシェーダーを使用している場合は、独自のメタパスを追加できます。

メタパスを使ったシェーダー例

下のシェーダーでは、ランタイムにマテリアルの外観に影響を与えることなく、ライティングのベイクシステムでのみ使用されるアルベド色とアルベドテクスチャを指定できます。この例では、放出は UV から取得されますが、それを制御するためにどんな値でも使用できます。

Shader "Custom/metaPassShader"{

    Properties {
        _Color ("Color", Color)=(1,1,1,1)
        _MainTex ("Albedo (RGB)",2D)="white"{}
        _Glossiness ("Smoothness", Range(0,1))=0.5
        _Metallic ("Metallic", Range(0,1))=0.0

        _GIAlbedoColor ("Color Albedo (GI)", Color)=(1,1,1,1)
        _GIAlbedoTex ("Albedo (GI)",2D)="white"{}
    }

    SubShader {
    // ------------------------------------------------------------------
    // Extracts information for lightmapping, GI (emission, albedo, ...)
    // This pass is not used during regular rendering.
        Pass
        {
            Name "META"
            Tags {"LightMode"="Meta"}
            Cull Off
            CGPROGRAM

            #include"UnityStandardMeta.cginc"

            sampler2D _GIAlbedoTex;
            fixed4 _GIAlbedoColor;
            float4 frag_meta2 (v2f_meta i): SV_Target
            {
                // We're interested in diffuse & specular colors
                // and surface roughness to produce final albedo.

                FragmentCommonData data = UNITY_SETUP_BRDF_INPUT (i.uv);
                UnityMetaInput o;
                UNITY_INITIALIZE_OUTPUT(UnityMetaInput, o);
                fixed4 c = tex2D (_GIAlbedoTex, i.uv);
                o.Albedo = fixed3(c.rgb * _GIAlbedoColor.rgb);
                o.Emission = Emission(i.uv.xy);
                return UnityMetaFragment(o);
            }

            #pragma vertex vert_meta
            #pragma fragment frag_meta2
            #pragma shader_feature _EMISSION
            #pragma shader_feature _METALLICGLOSSMAP
            #pragma shader_feature ___ _DETAIL_MULX2
            ENDCG
        }

        Tags {"RenderType"="Opaque"}
        LOD 200

        CGPROGRAM
        // Physically-based Standard lighting model, and enable shadows on all light types
        #pragma surface surf Standard fullforwardshadows nometa
        // Use Shader model 3.0 target, to get nicer looking lighting
        #pragma target 3.0

        sampler2D _MainTex;

        struct Input {
            float2 uv_MainTex;
        };

        half _Glossiness;
        half _Metallic;
        fixed4 _Color;

        void surf (Input IN,inout SurfaceOutputStandard o){
            // Albedo comes from a texture tinted by color
            fixed4 c = tex2D (_MainTex, IN.uv_MainTex)* _Color;
            o.Albedo = c.rgb;
            // Metallic and smoothness come from slider variables
            o.Metallic = _Metallic;
            o.Smoothness = _Glossiness;
            o.Alpha = c.a;
        }
        ENDCG
    }

    FallBack "Diffuse"
}

技術情報

Enlighten Realtime Global Illumination and lightmapping use Unity’s Meta Pass to extract albedo values from surfaces and handle diffuse transport themselves by using surface albedo on each bounce.

Metallic surfaces with a black (or almost black) albedo bounce very little light diffusely. Because the lightmappers handle only diffuse light transport, this means that you may see very little bounced light from these types of surfaces. Unity’s built-in Meta Passes account for this by providing a boosted version of the metal hue color instead of a physically correct albedo. This means that you get some bounce even from metallic materials. If you want a different behaviour, you can create a custom meta pass.

The built-in Meta Passes do not handle spectral specular reflectance.

Note: If you are using Enlighten Realtime Global Illumination, the Meta pass in the Player is not as fast as DynamicGI.SetEmissive, but it is more flexible because you are not limited to a single color.