Standard 2-faced shader problem

Questions & Answers
1

Hi,
Following tips on this forum, I’ve changed Unity Standard (specular setup) shader to allow back facing.
I added Cull Off to the shader code. Back faces are displayed now, but they are over-darkened.

108474-2-sided-shader.jpg
108474-2-sided-shader.jpg720×444 138 KB

Could someone help me with this problem? I just need to have back faces to be rendered just the same way as front faces.

Shader "DryGrass"
{
	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
		_GlossMapScale("Smoothness Factor", Range(0.0, 1.0)) = 1.0
		[Enum(Specular Alpha,0,Albedo Alpha,1)] _SmoothnessTextureChannel ("Smoothness texture channel", Float) = 0

		_SpecColor("Specular", Color) = (0.2,0.2,0.2)
		_SpecGlossMap("Specular", 2D) = "white" {}
		[ToggleOff] _SpecularHighlights("Specular Highlights", Float) = 1.0
		[ToggleOff] _GlossyReflections("Glossy Reflections", Float) = 1.0

		_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 SpecularSetup
	ENDCG

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

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

			Blend [_SrcBlend] [_DstBlend]
			ZWrite [_ZWrite]

			CGPROGRAM
			#pragma target 3.0

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

			#pragma shader_feature _NORMALMAP
			#pragma shader_feature _ _ALPHATEST_ON _ALPHABLEND_ON _ALPHAPREMULTIPLY_ON
			#pragma shader_feature _EMISSION
			#pragma shader_feature _SPECGLOSSMAP
			#pragma shader_feature ___ _DETAIL_MULX2
			#pragma shader_feature _ _SMOOTHNESS_TEXTURE_ALBEDO_CHANNEL_A
			#pragma shader_feature _ _SPECULARHIGHLIGHTS_OFF
			#pragma shader_feature _ _GLOSSYREFLECTIONS_OFF
			#pragma shader_feature _PARALLAXMAP

			#pragma multi_compile_fwdbase
			#pragma multi_compile_fog

			#pragma vertex vertBase
			#pragma fragment fragBase
			#include "UnityStandardCoreForward.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

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

			#pragma shader_feature _NORMALMAP
			#pragma shader_feature _ _ALPHATEST_ON _ALPHABLEND_ON _ALPHAPREMULTIPLY_ON
			#pragma shader_feature _SPECGLOSSMAP
			#pragma shader_feature _ _SMOOTHNESS_TEXTURE_ALBEDO_CHANNEL_A
			#pragma shader_feature _ _SPECULARHIGHLIGHTS_OFF
			#pragma shader_feature ___ _DETAIL_MULX2
			#pragma shader_feature _PARALLAXMAP

			#pragma multi_compile_fwdadd_fullshadows
			#pragma multi_compile_fog

			#pragma vertex vertAdd
			#pragma fragment fragAdd
			#include "UnityStandardCoreForward.cginc"

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

			CGPROGRAM
			#pragma target 3.0

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


			#pragma shader_feature _ _ALPHATEST_ON _ALPHABLEND_ON _ALPHAPREMULTIPLY_ON
			#pragma shader_feature _SPECGLOSSMAP
			#pragma shader_feature _PARALLAXMAP
			#pragma multi_compile_shadowcaster

			#pragma vertex vertShadowCaster
			#pragma fragment fragShadowCaster

			#include "UnityStandardShadow.cginc"

			ENDCG
		}
		// ------------------------------------------------------------------
		//  Deferred pass
		Pass
		{
			Name "DEFERRED"
			Tags { "LightMode" = "Deferred" }
            
			CGPROGRAM
			#pragma target 3.0
			#pragma exclude_renderers nomrt


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

			#pragma shader_feature _NORMALMAP
			#pragma shader_feature _ _ALPHATEST_ON _ALPHABLEND_ON _ALPHAPREMULTIPLY_ON
			#pragma shader_feature _EMISSION
			#pragma shader_feature _SPECGLOSSMAP
			#pragma shader_feature _ _SMOOTHNESS_TEXTURE_ALBEDO_CHANNEL_A
			#pragma shader_feature _ _SPECULARHIGHLIGHTS_OFF
			#pragma shader_feature ___ _DETAIL_MULX2
			#pragma shader_feature _PARALLAXMAP

			#pragma multi_compile ___ UNITY_HDR_ON
			#pragma multi_compile ___ LIGHTMAP_ON
			#pragma multi_compile ___ DIRLIGHTMAP_COMBINED DIRLIGHTMAP_SEPARATE
			#pragma multi_compile ___ 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 _SPECGLOSSMAP
			#pragma shader_feature _ _SMOOTHNESS_TEXTURE_ALBEDO_CHANNEL_A
			#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]

			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 _SPECGLOSSMAP
			#pragma shader_feature _ _SMOOTHNESS_TEXTURE_ALBEDO_CHANNEL_A
			#pragma shader_feature _ _SPECULARHIGHLIGHTS_OFF
			#pragma shader_feature _ _GLOSSYREFLECTIONS_OFF
			#pragma shader_feature ___ _DETAIL_MULX2
			// SM2.0: NOT SUPPORTED shader_feature _PARALLAXMAP

			#pragma skip_variants SHADOWS_SOFT DYNAMICLIGHTMAP_ON DIRLIGHTMAP_COMBINED DIRLIGHTMAP_SEPARATE
			
			#pragma multi_compile_fwdbase
			#pragma multi_compile_fog

			#pragma vertex vertBase
			#pragma fragment fragBase
			#include "UnityStandardCoreForward.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 _SPECGLOSSMAP
			#pragma shader_feature _ _SMOOTHNESS_TEXTURE_ALBEDO_CHANNEL_A
			#pragma shader_feature _ _SPECULARHIGHLIGHTS_OFF
			#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 vertAdd
			#pragma fragment fragAdd
			#include "UnityStandardCoreForward.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 shader_feature _SPECGLOSSMAP
			#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 _SPECGLOSSMAP
			#pragma shader_feature _ _SMOOTHNESS_TEXTURE_ALBEDO_CHANNEL_A
			#pragma shader_feature ___ _DETAIL_MULX2

			#include "UnityStandardMeta.cginc"
			ENDCG
		}*/
	}

	FallBack "VertexLit"
	CustomEditor "StandardShaderGUI"
}
2

I just need to have back faces to be
rendered just the same way as front
faces.

That’s not possible by just disabling backface culling. The lighting calculations are based on the vertex normals. Those can only point in one direction. The back faces would need inverted / mirrored normals in order to properly calculate lighting.

There are generally three solutions but not everyone may work with every shader variant:

  • Calculate the dot product between the worldspace vertex normal and the view direction. If the normal points away from the screen you could just invert the normal in the vertex shader. This however would only work for flat faces. Things like spheres or curved surfaces wouldn’t work.
  • Implement seperate passes for the front and back face and invert the normals in the back face pass.
  • Finally the solution that works in all cases is to actually render two faces. So your mesh should have a front facing and a back facing quad.

In theory it’s also possible to use the ddx / ddy partial derivative inside the fragment shader to calculate flat normal vector on the fly based on the surface tangents. However this is computationally quite expensive and not necessarily supported on all platforms. More information over here