[VFX] Add frontface semantic to vfx using shader graph materials (#257)

* Add frontface semantic to vfx using shader graph materials

* Update changelog

Author: gabrieldelacruz

com.unity.shadergraph/Editor/Data/Nodes/Utility/Logic/IsFrontFaceNode.cs

@@ -25,7 +25,7 @@ public override void UpdateNodeAfterDeserialization()
 
         public void GenerateNodeCode(ShaderStringBuilder sb, GenerationMode generationMode)
         {
-            sb.AppendLine(string.Format("$precision {0} = max(0, IN.{1});", GetVariableNameForSlot(OutputSlotId), ShaderGeneratorNames.FaceSign));
+            sb.AppendLine(string.Format("$precision {0} = max(0, IN.{1}.x);", GetVariableNameForSlot(OutputSlotId), ShaderGeneratorNames.FaceSign));
         }
 
         public bool RequiresFaceSign(ShaderStageCapability stageCapability = ShaderStageCapability.Fragment)

com.unity.visualeffectgraph/CHANGELOG.md

@@ -67,6 +67,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Enabled an optimization for motion vectors, storing projected positions for vertices instead of the transform matrix
 - Compilation issue when normal is used in shadergraph for opacity with unlit output
 - Fix Exception on trying to invert a degenerate TRS matrix [Case 1307068](https://issuetracker.unity3d.com/product/unity/issues/guid/1307068/)
+- Fix IsFrontFace shader graph node for VFX.
 
 ## [11.0.0] - 2020-10-21
 ### Added

com.unity.visualeffectgraph/Editor/ShaderGraph/VFXShaderGraphParticleOutput.cs

@@ -804,6 +804,11 @@ public override IEnumerable<KeyValuePair<string, VFXShaderWriter>> additionalRep
                             callSG.builder.AppendLine("INSG.TimeParameters = _TimeParameters.xyz;");
                         }
 
+                        if (graphCode.requirements.requiresFaceSign)
+                        {
+                            callSG.builder.AppendLine("INSG.FaceSign = frontFace ? 1.0f : -1.0f;");
+                        }
+
                         if (taskType == VFXTaskType.ParticleMeshOutput)
                         {
                             for (UVChannel uv = UVChannel.UV1; uv <= UVChannel.UV3; ++uv)

com.unity.visualeffectgraph/Shaders/ParticlePlanarPrimitives/PassForwardCommon.template

@@ -42,7 +42,7 @@ struct ps_input
 	#if SHADERGRAPH_NEEDS_TANGENT_FORWARD
 	float3 tangent : TEXCOORD7;
 	#endif
-	
+
 	${VFXAdditionalInterpolantsDeclaration}
 
 	UNITY_VERTEX_OUTPUT_STEREO
@@ -91,7 +91,8 @@ ${SHADERGRAPH_PIXEL_CODE_FORWARD}
 #endif
 
 #pragma fragment frag
-ps_output frag(ps_input i)
+ps_output frag(ps_input i,	
+	bool frontFace : SV_IsFrontFace)
 {
 	UNITY_SETUP_STEREO_EYE_INDEX_POST_VERTEX(i);
 	ps_output o = (ps_output)0;