Fix null geometry support

It was causing an issue on vulkan & d3d12 (and a warning in dx11) for planar primitive.
Took inspiration from the initial (dead code) "ModifyVertexEntry" : https://github.com/Unity-Technologies/Graphics/blob/2773810e9fb5e893e2d207ff048586414cc387e4/com.unity.render-pipelines.high-definition/Editor/VFXGraph/VFXHDRPSubTarget.cs#L132
There isn't a common factorization like @sebastienlagarde did with 2773810#diff-7174c990ca8df27503bf5973a949e19bc00cf239832d30b20b2a69167667272eL102 in URP, so, I'm restoring an optionnal "description" driven replacement of pragmas.
See also this thread https://unity.slack.com/archives/C01Q3N39UEB/p1629821649001500

Author: PaulDemeulenaere

com.unity.render-pipelines.high-definition/Editor/VFXGraph/VFXHDRPBinder.cs

@@ -130,7 +130,7 @@ public override IEnumerable<KeyValuePair<Type, string>> GetUnsupportedShaderProp
                 HDStructFields.AttributesMesh.indices,
 
                 // VertexID without the Preprocessor.
-                new FieldDescriptor(HDStructFields.AttributesMesh.name, "vertexID", "ATTRIBUTES_NEED_VERTEXID", ShaderValueType.Uint, "SV_VertexID")
+                new FieldDescriptor(HDStructFields.AttributesMesh.name, "vertexID", "ATTRIBUTES_NEED_VERTEXID", ShaderValueType.Uint, "VERTEXID_SEMANTIC")
             }
         };
 

com.unity.render-pipelines.universal/Editor/ShaderGraph/Templates/ShaderPass.template

@@ -128,5 +128,11 @@ $features.graphPixel: $include("SharedCode.template.hlsl")
 
 $splice(PostGraphIncludes)
 
+// --------------------------------------------------
+// Visual Effect Vertex Invocations
+#ifdef HAVE_VFX_MODIFICATION
+#include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/VisualEffectVertex.hlsl"
+#endif
+
 ENDHLSL
 }

com.unity.render-pipelines.universal/Editor/ShaderGraph/Templates/VFX/Config.template.hlsl

@@ -5,8 +5,6 @@ $splice(VFXDefineSpace)
 //VFXDefines splice
 $splice(VFXDefines)
 
-//TODOPAUL See VisualEffectVertex.hlsl in HDRP, special case for null geometry
-//TODOPAUL Test on vulkan/DX12
 #define NULL_GEOMETRY_INPUT defined(HAVE_VFX_PLANAR_PRIMITIVE)
 
 // Explicitly defined here for now (similar to how it was done in the previous VFX code-gen)

com.unity.render-pipelines.universal/Editor/ShaderGraph/Templates/VFX/ConfigPlanarPrimitive.template.hlsl

@@ -1,11 +1,14 @@
 // Output Type: Planar Primitive (Triangle, Quad, Octagon)
+//TODOPAUL : Factorize this file with HDRP moving it in VFX
 
 #if defined(HAS_STRIPS) && !defined(VFX_PRIMITIVE_QUAD)
 #error VFX_PRIMITIVE_QUAD must be defined when HAS_STRIPS is.
 #endif
 
 #define VFX_NON_UNIFORM_SCALE VFX_LOCAL_SPACE
 
+#define HAVE_VFX_PLANAR_PRIMITIVE
+
 bool GetMeshAndElementIndex(inout Attributes input, inout AttributesElement element)
 {
     uint id = input.vertexID;

com.unity.render-pipelines.universal/Editor/VFXGraph/VFXURPBinder.cs

@@ -90,7 +90,7 @@ public override VFXAbstractRenderedOutput.BlendMode GetBlendModeFromMaterial(VFX
                 StructFields.Attributes.indices,
 
                 // VertexID without the Preprocessor.
-                new FieldDescriptor(StructFields.Attributes.name, "vertexID", "ATTRIBUTES_NEED_VERTEXID", ShaderValueType.Uint, "SV_VertexID")
+                new FieldDescriptor(StructFields.Attributes.name, "vertexID", "ATTRIBUTES_NEED_VERTEXID", ShaderValueType.Uint, "VERTEXID_SEMANTIC")
             }
         };
 
@@ -187,6 +187,10 @@ public override ShaderGraphBinder GetShaderGraphDescriptor(VFXContext context, V
                 },
 
                 fieldDependencies = ElementSpaceDependencies,
+                pragmasReplacement = new (PragmaDescriptor, PragmaDescriptor)[]
+                {
+                    ( Pragma.Vertex("vert"), Pragma.Vertex("VertVFX") )
+                },
                 useFragInputs = false
             };
         }

com.unity.render-pipelines.universal/ShaderLibrary/VisualEffectVertex.hlsl

@@ -0,0 +1,18 @@
+// Wrapper vertex invocations for VFX. Necesarry to work around various null input geometry issues for vertex input layout on DX12 and Vulkan.
+#if NULL_GEOMETRY_INPUT
+PackedVaryings VertVFX(uint vertexID : VERTEXID_SEMANTIC, uint instanceID : INSTANCEID_SEMANTIC)
+{
+    Attributes input;
+    ZERO_INITIALIZE(Attributes, input);
+
+    input.vertexID = vertexID;
+    input.instanceID = instanceID;
+
+    return vert(input);
+}
+#else
+PackedVaryings VertVFX(Attributes input)
+{
+    return vert(input);
+}
+#endif

com.unity.render-pipelines.universal/ShaderLibrary/VisualEffectVertex.hlsl.meta

@@ -127,5 +127,11 @@ Pass
 
     $splice(PostGraphIncludes)
 
+    // --------------------------------------------------
+    // Visual Effect Vertex Invocations
+    #ifdef HAVE_VFX_MODIFICATION
+    #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/VisualEffectVertex.hlsl"
+    #endif
+
     ENDHLSL
 }

com.unity.shadergraph/Editor/Generation/Templates/PassMesh.template

@@ -18,6 +18,7 @@ public struct ShaderGraphBinder
         {
             public StructCollection structs;
             public DependencyCollection fieldDependencies;
+            public (PragmaDescriptor oldDesc, PragmaDescriptor newDesc)[] pragmasReplacement;
             public bool useFragInputs;
         }
 

com.unity.visualeffectgraph/Editor/Core/VFXSRPBinder.cs

@@ -231,6 +231,25 @@ static AdditionalCommandDescriptor GenerateFragInputs(VFXContext context, VFXCon
             return new AdditionalCommandDescriptor("FragInputsVFX", builder.ToString());
         }
 
+        static PragmaCollection ApplyPragmaReplacement(PragmaCollection pragmas, VFXSRPBinder.ShaderGraphBinder shaderGraphSRPInfo)
+        {
+            if (shaderGraphSRPInfo.pragmasReplacement != null)
+            {
+                var overridenPragmas = new PragmaCollection();
+                foreach (var pragma in pragmas)
+                {
+                    var currentPragma = pragma;
+                    var replacement = shaderGraphSRPInfo.pragmasReplacement.FirstOrDefault(o => o.oldDesc.value == pragma.descriptor.value);
+                    if (!string.IsNullOrEmpty(replacement.newDesc.value))
+                        currentPragma = new PragmaCollection.Item(replacement.newDesc, pragma.fieldConditions);
+
+                    overridenPragmas.Add(currentPragma.descriptor, currentPragma.fieldConditions);
+                }
+                return overridenPragmas;
+            }
+            return pragmas;
+        }
+
         internal static SubShaderDescriptor PostProcessSubShader(SubShaderDescriptor subShaderDescriptor, VFXContext context, VFXContextCompiledData data)
         {
             var srp = VFXLibrary.currentSRPBinder;
@@ -280,6 +299,8 @@ out var vertexPropertiesAssignDescriptor
             {
                 var passDescriptor = passes[i].descriptor;
 
+                passDescriptor.pragmas = ApplyPragmaReplacement(passDescriptor.pragmas, shaderGraphSRPInfo);
+
                 // Warning: We are replacing the struct provided in the regular pass. It is ok as for now the VFX editor don't support
                 // tessellation or raytracing
                 passDescriptor.structs = new StructCollection();