All scatter types now inherit from a common base

This is required for vtkm::worklet::Invoker to launch worklets
with a non default scatter type.

vtkm/worklet/ScatterCounting.h

@@ -10,6 +10,7 @@
 #ifndef vtk_m_worklet_ScatterCounting_h
 #define vtk_m_worklet_ScatterCounting_h
 
+#include <vtkm/worklet/internal/ScatterBase.h>
 #include <vtkm/worklet/vtkm_worklet_export.h>
 
 #include <vtkm/cont/VariantArrayHandle.h>
@@ -40,7 +41,7 @@ struct ScatterCountingBuilder;
 /// taken in the constructor and the index arrays are derived from that. So
 /// changing the counts after the scatter is created will have no effect.
 ///
-struct VTKM_WORKLET_EXPORT ScatterCounting
+struct VTKM_WORKLET_EXPORT ScatterCounting : internal::ScatterBase
 {
   struct CountTypes : vtkm::ListTagBase<vtkm::Int64,
                                         vtkm::Int32,

vtkm/worklet/ScatterIdentity.h

@@ -12,6 +12,7 @@
 
 #include <vtkm/cont/ArrayHandleConstant.h>
 #include <vtkm/cont/ArrayHandleIndex.h>
+#include <vtkm/worklet/internal/ScatterBase.h>
 
 namespace vtkm
 {
@@ -26,7 +27,7 @@ namespace worklet
 /// element generates one output element associated with it. This is the
 /// default for basic maps.
 ///
-struct ScatterIdentity
+struct ScatterIdentity : internal::ScatterBase
 {
   using OutputToInputMapType = vtkm::cont::ArrayHandleIndex;
   VTKM_CONT

vtkm/worklet/ScatterPermutation.h

@@ -12,6 +12,7 @@
 
 #include <vtkm/cont/ArrayHandle.h>
 #include <vtkm/cont/ArrayHandleConstant.h>
+#include <vtkm/worklet/internal/ScatterBase.h>
 
 namespace vtkm
 {
@@ -28,7 +29,7 @@ namespace worklet
 /// can be duplicates. Note that even with duplicates the VistIndex is always 0.
 ///
 template <typename PermutationStorage = VTKM_DEFAULT_STORAGE_TAG>
-class ScatterPermutation
+class ScatterPermutation : public internal::ScatterBase
 {
 private:
   using PermutationArrayHandle = vtkm::cont::ArrayHandle<vtkm::Id, PermutationStorage>;

vtkm/worklet/ScatterUniform.h

@@ -13,6 +13,7 @@
 #include <vtkm/cont/ArrayHandle.h>
 #include <vtkm/cont/ArrayHandleCounting.h>
 #include <vtkm/cont/ArrayHandleImplicit.h>
+#include <vtkm/worklet/internal/ScatterBase.h>
 
 namespace vtkm
 {
@@ -49,7 +50,7 @@ struct FunctorDiv
 /// elements are grouped by the input associated.
 ///
 template <vtkm::IdComponent NumOutputsPerInput>
-struct ScatterUniform
+struct ScatterUniform : internal::ScatterBase
 {
   VTKM_CONT ScatterUniform() = default;
 

vtkm/worklet/internal/CMakeLists.txt

@@ -10,6 +10,7 @@
 
 set(headers
   DispatcherBase.h
+  ScatterBase.h
   TriangulateTables.h
   WorkletBase.h
   )

vtkm/worklet/internal/ScatterBase.h

+//============================================================================
+//  Copyright (c) Kitware, Inc.
+//  All rights reserved.
+//  See LICENSE.txt for details.
+//
+//  This software is distributed WITHOUT ANY WARRANTY; without even
+//  the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
+//  PURPOSE.  See the above copyright notice for more information.
+//============================================================================
+#ifndef vtk_m_worklet_internal_ScatterBase_h
+#define vtk_m_worklet_internal_ScatterBase_h
+
+#include <vtkm/internal/ExportMacros.h>
+
+namespace vtkm
+{
+namespace worklet
+{
+namespace internal
+{
+
+/// Base class for all scatter classes.
+///
+/// This allows VTK-m to determine when a parameter
+/// is a scatter type instead of a worklet parameter.
+///
+struct VTKM_ALWAYS_EXPORT ScatterBase
+{
+};
+}
+}
+}
+#endif