StandardShaderを編集して、裏面も描画されるようにする

プロ生ちゃんのUnityモデルに同梱されている、StandardShaderを用いたバージョンのPrefabは、StandardShaderを素のまま使っていたので、裏地が表示されていませんでした。

左が素のStandardShaderを使って描画した時。
スカートに関しては、裏地用に別途内側が表面になっているメッシュが用意されているため、一見、裏地が表示されているように見えます。

遠巻きにモデルを見ている分には余り気になりませんが、ポーズによっては目立つので、StandardShaderを編集して、裏面も描画させるようにしました(上図の右側)。

参考：
Standard Shader 2-sided | Unity Community

>Download the built-in shaders, copy the Standard or StandardSpecular shader into your project, then add the "Cull Off" flag to the passes with the names "FORWARD" or "DEFERRED" (there are three total).

とあるように、デフォルトのStandardShaderのソースに対し、"FORWARD"と"DEFERRED"のPass
に"Cull Off"を追加しただけです(計3箇所)。

後日、公開しているデータにもShaderを同梱したいと思います。
なお、StandardAsset内のデータは再配布可能ということは知っていたのですが、ビルトインシェーダーに関しても改変・再配布は可能とのことです。

Shader "Custom/StandardDoubleSide"
{
	Properties
	{
		_Color("Color", Color) = (1,1,1,1)
		_MainTex("Albedo", 2D) = "white" {}
		
		_Cutoff("Alpha Cutoff", Range(0.0, 1.0)) = 0.5

		_Glossiness("Smoothness", Range(0.0, 1.0)) = 0.5
		[Gamma] _Metallic("Metallic", Range(0.0, 1.0)) = 0.0
		_MetallicGlossMap("Metallic", 2D) = "white" {}

		_BumpScale("Scale", Float) = 1.0
		_BumpMap("Normal Map", 2D) = "bump" {}

		_Parallax ("Height Scale", Range (0.005, 0.08)) = 0.02
		_ParallaxMap ("Height Map", 2D) = "black" {}

		_OcclusionStrength("Strength", Range(0.0, 1.0)) = 1.0
		_OcclusionMap("Occlusion", 2D) = "white" {}

		_EmissionColor("Color", Color) = (0,0,0)
		_EmissionMap("Emission", 2D) = "white" {}
		
		_DetailMask("Detail Mask", 2D) = "white" {}

		_DetailAlbedoMap("Detail Albedo x2", 2D) = "grey" {}
		_DetailNormalMapScale("Scale", Float) = 1.0
		_DetailNormalMap("Normal Map", 2D) = "bump" {}

		[Enum(UV0,0,UV1,1)] _UVSec ("UV Set for secondary textures", Float) = 0


		// Blending state
		[HideInInspector] _Mode ("__mode", Float) = 0.0
		[HideInInspector] _SrcBlend ("__src", Float) = 1.0
		[HideInInspector] _DstBlend ("__dst", Float) = 0.0
		[HideInInspector] _ZWrite ("__zw", Float) = 1.0
	}

	CGINCLUDE
		#define UNITY_SETUP_BRDF_INPUT MetallicSetup
	ENDCG

	SubShader
	{
		Tags { "RenderType"="Opaque" "PerformanceChecks"="False" }
		LOD 300
	

		// ------------------------------------------------------------------
		//  Base forward pass (directional light, emission, lightmaps, ...)
		Pass
		{
			Name "FORWARD" 
			Tags { "LightMode" = "ForwardBase" }

			Blend [_SrcBlend] [_DstBlend]
			ZWrite [_ZWrite]
			
			Cull Off
			CGPROGRAM
			#pragma target 3.0
			// TEMPORARY: GLES2.0 temporarily disabled to prevent errors spam on devices without textureCubeLodEXT
			#pragma exclude_renderers gles
			
			// -------------------------------------
					
			#pragma shader_feature _NORMALMAP
			#pragma shader_feature _ _ALPHATEST_ON _ALPHABLEND_ON _ALPHAPREMULTIPLY_ON
			#pragma shader_feature _EMISSION
			#pragma shader_feature _METALLICGLOSSMAP 
			#pragma shader_feature ___ _DETAIL_MULX2
			#pragma shader_feature _PARALLAXMAP
			
			#pragma multi_compile_fwdbase
			#pragma multi_compile_fog
				
			#pragma vertex vertForwardBase
			#pragma fragment fragForwardBase

			#include "UnityStandardCore.cginc"

			ENDCG
		}
		// ------------------------------------------------------------------
		//  Additive forward pass (one light per pass)
		Pass
		{
			Name "FORWARD_DELTA"
			Tags { "LightMode" = "ForwardAdd" }
			Blend [_SrcBlend] One
			Fog { Color (0,0,0,0) } // in additive pass fog should be black
			ZWrite Off
			ZTest LEqual

			CGPROGRAM
			#pragma target 3.0
			// GLES2.0 temporarily disabled to prevent errors spam on devices without textureCubeLodEXT
			#pragma exclude_renderers gles

			// -------------------------------------

			
			#pragma shader_feature _NORMALMAP
			#pragma shader_feature _ _ALPHATEST_ON _ALPHABLEND_ON _ALPHAPREMULTIPLY_ON
			#pragma shader_feature _METALLICGLOSSMAP
			#pragma shader_feature ___ _DETAIL_MULX2
			#pragma shader_feature _PARALLAXMAP
			
			#pragma multi_compile_fwdadd_fullshadows
			#pragma multi_compile_fog
			
			#pragma vertex vertForwardAdd
			#pragma fragment fragForwardAdd

			#include "UnityStandardCore.cginc"

			ENDCG
		}
		// ------------------------------------------------------------------
		//  Shadow rendering pass
		Pass {
			Name "ShadowCaster"
			Tags { "LightMode" = "ShadowCaster" }
			
			ZWrite On ZTest LEqual

			CGPROGRAM
			#pragma target 3.0
			// TEMPORARY: GLES2.0 temporarily disabled to prevent errors spam on devices without textureCubeLodEXT
			#pragma exclude_renderers gles
			
			// -------------------------------------


			#pragma shader_feature _ _ALPHATEST_ON _ALPHABLEND_ON _ALPHAPREMULTIPLY_ON
			#pragma multi_compile_shadowcaster

			#pragma vertex vertShadowCaster
			#pragma fragment fragShadowCaster

			#include "UnityStandardShadow.cginc"

			ENDCG
		}
		// ------------------------------------------------------------------
		//  Deferred pass
		Pass
		{
			Name "DEFERRED"
			Tags { "LightMode" = "Deferred" }

			Cull Off
			CGPROGRAM
			#pragma target 3.0
			// TEMPORARY: GLES2.0 temporarily disabled to prevent errors spam on devices without textureCubeLodEXT
			#pragma exclude_renderers nomrt gles
			

			// -------------------------------------

			#pragma shader_feature _NORMALMAP
			#pragma shader_feature _ _ALPHATEST_ON _ALPHABLEND_ON _ALPHAPREMULTIPLY_ON
			#pragma shader_feature _EMISSION
			#pragma shader_feature _METALLICGLOSSMAP
			#pragma shader_feature ___ _DETAIL_MULX2
			#pragma shader_feature _PARALLAXMAP

			#pragma multi_compile ___ UNITY_HDR_ON
			#pragma multi_compile LIGHTMAP_OFF LIGHTMAP_ON
			#pragma multi_compile DIRLIGHTMAP_OFF DIRLIGHTMAP_COMBINED DIRLIGHTMAP_SEPARATE
			#pragma multi_compile DYNAMICLIGHTMAP_OFF DYNAMICLIGHTMAP_ON
			
			#pragma vertex vertDeferred
			#pragma fragment fragDeferred

			#include "UnityStandardCore.cginc"

			ENDCG
		}

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

			Cull Off

			CGPROGRAM
			#pragma vertex vert_meta
			#pragma fragment frag_meta

			#pragma shader_feature _EMISSION
			#pragma shader_feature _METALLICGLOSSMAP
			#pragma shader_feature ___ _DETAIL_MULX2

			#include "UnityStandardMeta.cginc"
			ENDCG
		}
	}

	SubShader
	{
		Tags { "RenderType"="Opaque" "PerformanceChecks"="False" }
		LOD 150

		// ------------------------------------------------------------------
		//  Base forward pass (directional light, emission, lightmaps, ...)
		Pass
		{
			Name "FORWARD" 
			Tags { "LightMode" = "ForwardBase" }

			Blend [_SrcBlend] [_DstBlend]
			ZWrite [_ZWrite]

			Cull Off
			CGPROGRAM
			#pragma target 2.0
			
			#pragma shader_feature _NORMALMAP
			#pragma shader_feature _ _ALPHATEST_ON _ALPHABLEND_ON _ALPHAPREMULTIPLY_ON
			#pragma shader_feature _EMISSION 
			#pragma shader_feature _METALLICGLOSSMAP 
			#pragma shader_feature ___ _DETAIL_MULX2
			// SM2.0: NOT SUPPORTED shader_feature _PARALLAXMAP

			#pragma skip_variants SHADOWS_SOFT DIRLIGHTMAP_COMBINED DIRLIGHTMAP_SEPARATE

			#pragma multi_compile_fwdbase
			#pragma multi_compile_fog
	
			#pragma vertex vertForwardBase
			#pragma fragment fragForwardBase

			#include "UnityStandardCore.cginc"

			ENDCG
		}
		// ------------------------------------------------------------------
		//  Additive forward pass (one light per pass)
		Pass
		{
			Name "FORWARD_DELTA"
			Tags { "LightMode" = "ForwardAdd" }
			Blend [_SrcBlend] One
			Fog { Color (0,0,0,0) } // in additive pass fog should be black
			ZWrite Off
			ZTest LEqual
			
			CGPROGRAM
			#pragma target 2.0

			#pragma shader_feature _NORMALMAP
			#pragma shader_feature _ _ALPHATEST_ON _ALPHABLEND_ON _ALPHAPREMULTIPLY_ON
			#pragma shader_feature _METALLICGLOSSMAP
			#pragma shader_feature ___ _DETAIL_MULX2
			// SM2.0: NOT SUPPORTED shader_feature _PARALLAXMAP
			#pragma skip_variants SHADOWS_SOFT
			
			#pragma multi_compile_fwdadd_fullshadows
			#pragma multi_compile_fog
			
			#pragma vertex vertForwardAdd
			#pragma fragment fragForwardAdd

			#include "UnityStandardCore.cginc"

			ENDCG
		}
		// ------------------------------------------------------------------
		//  Shadow rendering pass
		Pass {
			Name "ShadowCaster"
			Tags { "LightMode" = "ShadowCaster" }
			
			ZWrite On ZTest LEqual

			CGPROGRAM
			#pragma target 2.0

			#pragma shader_feature _ _ALPHATEST_ON _ALPHABLEND_ON _ALPHAPREMULTIPLY_ON
			#pragma skip_variants SHADOWS_SOFT
			#pragma multi_compile_shadowcaster

			#pragma vertex vertShadowCaster
			#pragma fragment fragShadowCaster

			#include "UnityStandardShadow.cginc"

			ENDCG
		}

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

			Cull Off

			CGPROGRAM
			#pragma vertex vert_meta
			#pragma fragment frag_meta

			#pragma shader_feature _EMISSION
			#pragma shader_feature _METALLICGLOSSMAP
			#pragma shader_feature ___ _DETAIL_MULX2

			#include "UnityStandardMeta.cginc"
			ENDCG
		}
	}

	FallBack "VertexLit"
	CustomEditor "StandardShaderGUI"
}