[unity] Added support for double-sided lighting at SkeletonLit shaders (including URP and LWRP packages). Closes #1730.

spine-unity/Assets/Spine/Runtime/spine-unity/Shaders/CGIncludes/Spine-Skeleton-Lit-Common.cginc

@@ -83,7 +83,13 @@ VertexOutput vert (appdata v) {
 	float3 eyePos = UnityObjectToViewPos(float4(v.pos, 1)).xyz; //mul(UNITY_MATRIX_MV, float4(v.pos,1)).xyz;
 	half3 fixedNormal = half3(0,0,-1);
 	half3 eyeNormal = normalize(mul((float3x3)UNITY_MATRIX_IT_MV, fixedNormal));
-	//half3 eyeNormal = half3(0,0,1);
+
+#ifdef _DOUBLE_SIDED_LIGHTING
+	// unfortunately we have to compute the sign here in the vertex shader
+	// instead of using VFACE in fragment shader stage.
+	half faceSign = sign(eyeNormal.z);
+	eyeNormal *= faceSign;
+#endif
 
 	// Lights
 	half3 lcolor = half4(0,0,0,1).rgb + color.rgb * glstate_lightmodel_ambient.rgb;

spine-unity/Assets/Spine/Runtime/spine-unity/Shaders/Outline/Spine-Skeleton-Lit-Outline.shader

@@ -5,6 +5,7 @@ Shader "Spine/Outline/Skeleton Lit" {
 		_Cutoff ("Shadow alpha cutoff", Range(0,1)) = 0.1
 		[NoScaleOffset] _MainTex ("Main Texture", 2D) = "black" {}
 		[Toggle(_STRAIGHT_ALPHA_INPUT)] _StraightAlphaInput("Straight Alpha Texture", Int) = 0
+		[Toggle(_DOUBLE_SIDED_LIGHTING)] _DoubleSidedLighting("Double-Sided Lighting", Int) = 0
 		[HideInInspector] _StencilRef("Stencil Reference", Float) = 1.0
 		[HideInInspector][Enum(UnityEngine.Rendering.CompareFunction)] _StencilComp("Stencil Comparison", Float) = 8 // Set to Always as default
 

spine-unity/Assets/Spine/Runtime/spine-unity/Shaders/Outline/Spine-Skeleton-Lit-ZWrite-Outline.shader

@@ -6,6 +6,7 @@ Shader "Spine/Outline/Skeleton Lit ZWrite" {
 		_ShadowAlphaCutoff ("Shadow alpha cutoff", Range(0,1)) = 0.1
 		[NoScaleOffset] _MainTex ("Main Texture", 2D) = "black" {}
 		[Toggle(_STRAIGHT_ALPHA_INPUT)] _StraightAlphaInput("Straight Alpha Texture", Int) = 0
+		[Toggle(_DOUBLE_SIDED_LIGHTING)] _DoubleSidedLighting("Double-Sided Lighting", Int) = 0
 		[HideInInspector] _StencilRef("Stencil Reference", Float) = 1.0
 		[HideInInspector][Enum(UnityEngine.Rendering.CompareFunction)] _StencilComp("Stencil Comparison", Float) = 8 // Set to Always as default
 

spine-unity/Assets/Spine/Runtime/spine-unity/Shaders/Spine-Skeleton-Lit-ZWrite.shader

@@ -8,6 +8,7 @@ Shader "Spine/Skeleton Lit ZWrite" {
 		_ShadowAlphaCutoff ("Shadow alpha cutoff", Range(0,1)) = 0.1
 		[NoScaleOffset] _MainTex ("Main Texture", 2D) = "black" {}
 		[Toggle(_STRAIGHT_ALPHA_INPUT)] _StraightAlphaInput("Straight Alpha Texture", Int) = 0
+		[Toggle(_DOUBLE_SIDED_LIGHTING)] _DoubleSidedLighting("Double-Sided Lighting", Int) = 0
 		[HideInInspector] _StencilRef("Stencil Reference", Float) = 1.0
 		[HideInInspector][Enum(UnityEngine.Rendering.CompareFunction)] _StencilComp("Stencil Comparison", Float) = 8 // Set to Always as default
 
@@ -42,6 +43,7 @@ Shader "Spine/Skeleton Lit ZWrite" {
 
 			CGPROGRAM
 			#pragma shader_feature _ _STRAIGHT_ALPHA_INPUT
+			#pragma shader_feature _ _DOUBLE_SIDED_LIGHTING
 			#pragma vertex vert
 			#pragma fragment frag
 			#pragma target 2.0

spine-unity/Assets/Spine/Runtime/spine-unity/Shaders/Spine-Skeleton-Lit.shader

@@ -7,6 +7,7 @@ Shader "Spine/Skeleton Lit" {
 		_Cutoff ("Shadow alpha cutoff", Range(0,1)) = 0.1
 		[NoScaleOffset] _MainTex ("Main Texture", 2D) = "black" {}
 		[Toggle(_STRAIGHT_ALPHA_INPUT)] _StraightAlphaInput("Straight Alpha Texture", Int) = 0
+		[Toggle(_DOUBLE_SIDED_LIGHTING)] _DoubleSidedLighting("Double-Sided Lighting", Int) = 0
 		[HideInInspector] _StencilRef("Stencil Reference", Float) = 1.0
 		[HideInInspector][Enum(UnityEngine.Rendering.CompareFunction)] _StencilComp("Stencil Comparison", Float) = 8 // Set to Always as default
 
@@ -41,6 +42,7 @@ Shader "Spine/Skeleton Lit" {
 
 			CGPROGRAM
 			#pragma shader_feature _ _STRAIGHT_ALPHA_INPUT
+			#pragma shader_feature _ _DOUBLE_SIDED_LIGHTING
 			#pragma vertex vert
 			#pragma fragment frag
 			#pragma target 2.0

spine-unity/Modules/com.esotericsoftware.spine.lwrp-shaders/Shaders/CGIncludes/Spine-SkeletonLit-ForwardPass-LW.hlsl

@@ -6,7 +6,7 @@ struct appdata {
 	float3 normal : NORMAL;
 	half4 color : COLOR;
 	float2 uv0 : TEXCOORD0;
-	
+
 	UNITY_VERTEX_INPUT_INSTANCE_ID
 };
 
@@ -44,6 +44,15 @@ VertexOutput vert(appdata v) {
 	float3 positionWS = TransformObjectToWorld(v.pos);
 	half3 fixedNormal = half3(0, 0, -1);
 	half3 normalWS = normalize(mul((float3x3)unity_ObjectToWorld, fixedNormal));
+
+#ifdef _DOUBLE_SIDED_LIGHTING
+	// unfortunately we have to compute the sign here in the vertex shader
+	// instead of using VFACE in fragment shader stage.
+	half3 viewDirWS = UNITY_MATRIX_V[2].xyz;
+	half faceSign = sign(dot(viewDirWS, normalWS));
+	normalWS *= faceSign;
+#endif
+
 	color.rgb = LightweightLightVertexSimplified(positionWS, normalWS);
 
 	// Note: ambient light is also handled via SH.

spine-unity/Modules/com.esotericsoftware.spine.lwrp-shaders/Shaders/Spine-SkeletonLit-LW.shader

@@ -7,6 +7,7 @@ Shader "Lightweight Render Pipeline/Spine/Skeleton Lit" {
 		_Cutoff ("Shadow alpha cutoff", Range(0,1)) = 0.1
 		[NoScaleOffset] _MainTex ("Main Texture", 2D) = "black" {}
 		[Toggle(_STRAIGHT_ALPHA_INPUT)] _StraightAlphaInput("Straight Alpha Texture", Int) = 0
+		[Toggle(_DOUBLE_SIDED_LIGHTING)] _DoubleSidedLighting("Double-Sided Lighting", Int) = 0
 		[HideInInspector] _StencilRef("Stencil Reference", Float) = 1.0
 		[Enum(UnityEngine.Rendering.CompareFunction)] _StencilComp("Stencil Compare", Float) = 0.0 // Disabled stencil test by default
 	}
@@ -19,7 +20,7 @@ Shader "Lightweight Render Pipeline/Spine/Skeleton Lit" {
 		Cull Off
 		ZWrite Off
 		Blend One OneMinusSrcAlpha
-		
+
 		Stencil {
 			Ref[_StencilRef]
 			Comp[_StencilComp]
@@ -48,7 +49,7 @@ Shader "Lightweight Render Pipeline/Spine/Skeleton Lit" {
 			#pragma multi_compile _ _ADDITIONAL_LIGHT_SHADOWS
 			#pragma multi_compile _ _SHADOWS_SOFT
 			#pragma multi_compile _ _MIXED_LIGHTING_SUBTRACTIVE
-			
+
 			// -------------------------------------
 			// Unity defined keywords
 			#pragma multi_compile_fog
@@ -60,6 +61,7 @@ Shader "Lightweight Render Pipeline/Spine/Skeleton Lit" {
 			//--------------------------------------
 			// Spine related keywords
 			#pragma shader_feature _ _STRAIGHT_ALPHA_INPUT
+			#pragma shader_feature _ _DOUBLE_SIDED_LIGHTING
 			#pragma vertex vert
 			#pragma fragment frag
 			#pragma target 2.0

spine-unity/Modules/com.esotericsoftware.spine.urp-shaders/Shaders/Include/Spine-SkeletonLit-ForwardPass-URP.hlsl

@@ -44,6 +44,15 @@ VertexOutput vert(appdata v) {
 	float3 positionWS = TransformObjectToWorld(v.pos);
 	half3 fixedNormal = half3(0, 0, -1);
 	half3 normalWS = normalize(mul((float3x3)unity_ObjectToWorld, fixedNormal));
+
+#ifdef _DOUBLE_SIDED_LIGHTING
+	// unfortunately we have to compute the sign here in the vertex shader
+	// instead of using VFACE in fragment shader stage.
+	half3 viewDirWS = UNITY_MATRIX_V[2].xyz;
+	half faceSign = sign(dot(viewDirWS, normalWS));
+	normalWS *= faceSign;
+#endif
+
 	color.rgb = LightweightLightVertexSimplified(positionWS, normalWS);
 
 	// Note: ambient light is also handled via SH.

spine-unity/Modules/com.esotericsoftware.spine.urp-shaders/Shaders/Spine-SkeletonLit-URP.shader

@@ -3,6 +3,7 @@
 		_Cutoff ("Shadow alpha cutoff", Range(0,1)) = 0.1
 		[NoScaleOffset] _MainTex ("Main Texture", 2D) = "black" {}
 		[Toggle(_STRAIGHT_ALPHA_INPUT)] _StraightAlphaInput("Straight Alpha Texture", Int) = 0
+		[Toggle(_DOUBLE_SIDED_LIGHTING)] _DoubleSidedLighting("Double-Sided Lighting", Int) = 0
 		[HideInInspector] _StencilRef("Stencil Reference", Float) = 1.0
 		[Enum(UnityEngine.Rendering.CompareFunction)] _StencilComp("Stencil Compare", Float) = 0.0 // Disabled stencil test by default
 	}
@@ -55,6 +56,7 @@
 			//--------------------------------------
 			// Spine related keywords
 			#pragma shader_feature _ _STRAIGHT_ALPHA_INPUT
+			#pragma shader_feature _ _DOUBLE_SIDED_LIGHTING
 			#pragma vertex vert
 			#pragma fragment frag