From 84e3a1d118fdb23c7f60e9dec941d8ed47c8df37 Mon Sep 17 00:00:00 2001
From: piespy <63455655+piespy@users.noreply.github.com>
Date: Sun, 21 Sep 2025 12:15:51 +0200
Subject: [PATCH 1/3] Fix incorrect normals of two-sided materials; optional
 define to disable this

Use VFACE pixel shader semantic to determine which side of a two-sided material is drawn, and adjust normal vector. This allows e.g. lighting to apply to both sides.

Define MATERIAL_SINGLESIDE in a material file to disable this.
---
 Materials/material_common_2.0.fxsub | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/Materials/material_common_2.0.fxsub b/Materials/material_common_2.0.fxsub
index ae77ad2c..b7a5bdd5 100644
--- a/Materials/material_common_2.0.fxsub
+++ b/Materials/material_common_2.0.fxsub
@@ -1542,11 +1542,17 @@ GbufferParam MaterialPS(
 	in float2 coord0   : TEXCOORD1,
 #if OCCLUSION_MAP_TYPE == 2 || OCCLUSION_MAP_TYPE == 3
 	in float2 coord1   : TEXCOORD2,
+#endif
+#ifndef MATERIAL_SINGLESIDE
+	in float  faceside : VFACE,
 #endif
 	in float4 worldPos : TEXCOORD3)
 {
 	normal = normalize(normal);
 
+#ifdef MATERIAL_SINGLESIDE
+	float faceside = 1;
+#endif
 #if PARALLAX_MAP_FROM
 	#if PARALLAX_MAP_UV_FLIP
 		coord0.y = 1 - coord0.y;
@@ -1566,7 +1572,7 @@ GbufferParam MaterialPS(
 
 	MaterialParam material;
 	material.albedo = GetSubAlbedo(GetAlbedo(coord0), coord0);
-	material.normal = GetNormal(normal, worldPos.xyz, coord0);
+	material.normal = GetNormal(normal, worldPos.xyz, coord0) * faceside;
 #if SPECULAR_ANTIALIASING_ENABLE
 	material.smoothness = GeometricNormalFiltering(GetSmoothness(coord0), material.normal, specularAntiAliasingVariance, specularAntiAliasingThreshold);
 #else
@@ -1594,11 +1600,17 @@ GbufferParam Material2PS(
 	in float2 coord0   : TEXCOORD1,
 #if OCCLUSION_MAP_TYPE == 2 || OCCLUSION_MAP_TYPE == 3
 	in float2 coord1   : TEXCOORD2,
+#endif
+#ifndef MATERIAL_SINGLESIDE
+	in float  faceside : VFACE,
 #endif
 	in float4 worldPos : TEXCOORD3)
 {
 	normal = normalize(normal);
 
+#ifdef MATERIAL_SINGLESIDE
+	float faceside = 1;
+#endif
 #if PARALLAX_MAP_FROM
 	#if PARALLAX_MAP_UV_FLIP
 		coord0.y = 1 - coord0.y;
@@ -1623,7 +1635,7 @@ GbufferParam Material2PS(
 
 	MaterialParam material;
 	material.albedo = GetSubAlbedo(GetAlbedo(coord0), coord0);
-	material.normal = GetNormal(normal, worldPos.xyz, coord0);
+	material.normal = GetNormal(normal, worldPos.xyz, coord0) * faceside;
 	material.smoothness = min(geometricSmoothness, GetSmoothness(coord0));
 	material.metalness = GetMetalness(coord0);
 	material.specular = GetSpecular(coord0);
@@ -1677,4 +1689,5 @@ OBJECT_TEC(MainTecBS0, "object_ss")
 
 technique EdgeTec<string MMDPass = "edge";>{}
 technique ShadowTech<string MMDPass = "shadow";>{}
-technique ZplotTec<string MMDPass = "zplot";>{}
\ No newline at end of file
+
+technique ZplotTec<string MMDPass = "zplot";>{}

From a0901ae653ddd917f9b521f161a6c64e3935abd2 Mon Sep 17 00:00:00 2001
From: piespy <63455655+piespy@users.noreply.github.com>
Date: Sun, 21 Sep 2025 12:25:30 +0200
Subject: [PATCH 2/3] Fix incorrect normals of two-sided materials; optional
 define to disable

Use VFACE pixel shader semantic to determine which side of a two-sided material is drawn, and adjust normal vector. This allows e.g. lighting to apply to both sides.

Define MATERIAL_SINGLESIDE in a material file to disable this.
---
 Materials/material_common_2.0.fxsub | 1 -
 1 file changed, 1 deletion(-)

diff --git a/Materials/material_common_2.0.fxsub b/Materials/material_common_2.0.fxsub
index b7a5bdd5..956a362d 100644
--- a/Materials/material_common_2.0.fxsub
+++ b/Materials/material_common_2.0.fxsub
@@ -1689,5 +1689,4 @@ OBJECT_TEC(MainTecBS0, "object_ss")
 
 technique EdgeTec<string MMDPass = "edge";>{}
 technique ShadowTech<string MMDPass = "shadow";>{}
-
 technique ZplotTec<string MMDPass = "zplot";>{}

From 53f8aee64aa665491bca1f66cc70d2cd12741aeb Mon Sep 17 00:00:00 2001
From: piespy <63455655+piespy@users.noreply.github.com>
Date: Sun, 21 Sep 2025 12:29:15 +0200
Subject: [PATCH 3/3] Fix incorrect normals of two-sided materials; optional
 define to disable this

Use VFACE pixel shader semantic to determine which side of a two-sided material is drawn, and adjust normal vector. This allows e.g. lighting to apply to both sides.

Define MATERIAL_SINGLESIDE in a material file to disable this.