From ed04eda51bea802ea04e0156b5052b3cf5041fac Mon Sep 17 00:00:00 2001
From: assiduous <assiduous@diligentgraphics.com>
Date: Thu, 16 Jan 2025 19:16:17 -0800
Subject: [PATCH] HnMeshUtils: added GetTotalIndexCount function

---
 Hydrogent/include/HnMeshUtils.hpp | 13 +++++++++++++
 Hydrogent/src/HnMeshUtils.cpp     | 31 +++++++++++++++++++++++++++++++
 2 files changed, 44 insertions(+)

diff --git a/Hydrogent/include/HnMeshUtils.hpp b/Hydrogent/include/HnMeshUtils.hpp
index ffbb1990..d0988381 100644
--- a/Hydrogent/include/HnMeshUtils.hpp
+++ b/Hydrogent/include/HnMeshUtils.hpp
@@ -28,6 +28,7 @@
 
 #include "pxr/imaging/hd/types.h"
 #include "pxr/imaging/hd/meshTopology.h"
+#include "FlagEnum.h"
 
 namespace Diligent
 {
@@ -65,6 +66,17 @@ class HnMeshUtils final
     size_t GetNumEdges(size_t* NumFaces = nullptr) const;
 
 
+    enum GET_TOTAL_INDEX_COUNT_FLAGS : uint32_t
+    {
+        GET_TOTAL_INDEX_COUNT_FLAG_NONE        = 0u,
+        GET_TOTAL_INDEX_COUNT_FLAG_TRIANGLES   = 1u << 0u,
+        GET_TOTAL_INDEX_COUNT_FLAG_EDGES_LIST  = 1u << 1u,
+        GET_TOTAL_INDEX_COUNT_FLAG_EDGES_STRIP = 1u << 2u,
+        GET_TOTAL_INDEX_COUNT_FLAG_POINTS      = 1u << 3u,
+    };
+    /// Returns the total number of indices (triangles + edges + points)
+    size_t GetTotalIndexCount(GET_TOTAL_INDEX_COUNT_FLAGS Flags) const;
+
     /// Triangulates the mesh and returns the triangle indices and the start of each subset.
     ///
     /// \param[in]  UseFaceVertexIndices - Whether to use face vertex indices.
@@ -207,6 +219,7 @@ class HnMeshUtils final
     const pxr::HdMeshTopology& m_Topology;
     const pxr::SdfPath&        m_MeshId;
 };
+DEFINE_FLAG_ENUM_OPERATORS(HnMeshUtils::GET_TOTAL_INDEX_COUNT_FLAGS);
 
 } // namespace USD
 
diff --git a/Hydrogent/src/HnMeshUtils.cpp b/Hydrogent/src/HnMeshUtils.cpp
index 6b4e4c69..9cb3357a 100644
--- a/Hydrogent/src/HnMeshUtils.cpp
+++ b/Hydrogent/src/HnMeshUtils.cpp
@@ -105,6 +105,7 @@ void HnMeshUtils::Triangulate(bool                UseFaceVertexIndices,
 
     // Count the number of triangles
     const size_t NumTriangles = GetNumTriangles();
+    VERIFY_EXPR(NumTriangles * 3 == GetTotalIndexCount(GET_TOTAL_INDEX_COUNT_FLAG_TRIANGLES));
 
     // Triangulate faces
     TriangleIndices.reserve(NumTriangles);
@@ -280,6 +281,7 @@ pxr::VtIntArray HnMeshUtils::ComputeEdgeIndices(bool UseFaceVertexIndices, bool
                 EdgeIndices.push_back(-1);
             });
         VERIFY_EXPR(EdgeIndices.size() == NumEdges + NumFaces * 2);
+        VERIFY_EXPR(EdgeIndices.size() == GetTotalIndexCount(GET_TOTAL_INDEX_COUNT_FLAG_EDGES_STRIP));
     }
     else
     {
@@ -295,6 +297,7 @@ pxr::VtIntArray HnMeshUtils::ComputeEdgeIndices(bool UseFaceVertexIndices, bool
                 EdgeIndices.push_back(StartVertex);
             });
         VERIFY_EXPR(EdgeIndices.size() == NumEdges * 2);
+        VERIFY_EXPR(EdgeIndices.size() == GetTotalIndexCount(GET_TOTAL_INDEX_COUNT_FLAG_EDGES_LIST));
     }
 
     if (UseFaceVertexIndices)
@@ -320,6 +323,7 @@ pxr::VtIntArray HnMeshUtils::ComputePointIndices(bool ConvertToFaceVarying) cons
 
     pxr::VtIntArray PointIndices;
     PointIndices.reserve(NumPoints);
+    VERIFY_EXPR(static_cast<size_t>(NumPoints) == GetTotalIndexCount(GET_TOTAL_INDEX_COUNT_FLAG_POINTS));
     if (ConvertToFaceVarying)
     {
         const int*   FaceVertexIndices = m_Topology.GetFaceVertexIndices().cdata();
@@ -356,6 +360,33 @@ pxr::VtIntArray HnMeshUtils::ComputePointIndices(bool ConvertToFaceVarying) cons
     return PointIndices;
 }
 
+size_t HnMeshUtils::GetTotalIndexCount(GET_TOTAL_INDEX_COUNT_FLAGS Flags) const
+{
+    VERIFY((Flags & (GET_TOTAL_INDEX_COUNT_FLAG_EDGES_LIST | GET_TOTAL_INDEX_COUNT_FLAG_EDGES_STRIP)) != (GET_TOTAL_INDEX_COUNT_FLAG_EDGES_LIST | GET_TOTAL_INDEX_COUNT_FLAG_EDGES_STRIP),
+           "COUNT_EDGES_LIST and COUNT_EDGES_STRIP flags are mutually exclusive");
+
+    size_t NumIndices = 0;
+    if (Flags & GET_TOTAL_INDEX_COUNT_FLAG_TRIANGLES)
+    {
+        size_t NumTriangles = GetNumTriangles();
+        NumIndices += NumTriangles * 3;
+    }
+
+    if (Flags & (GET_TOTAL_INDEX_COUNT_FLAG_EDGES_LIST | GET_TOTAL_INDEX_COUNT_FLAG_EDGES_STRIP))
+    {
+        size_t NumFaces = 0;
+        size_t NumEdges = GetNumEdges(&NumFaces);
+        NumIndices += (Flags & GET_TOTAL_INDEX_COUNT_FLAG_EDGES_STRIP) ? NumEdges + NumFaces * 2 : NumEdges * 2;
+    }
+
+    if (Flags & GET_TOTAL_INDEX_COUNT_FLAG_POINTS)
+    {
+        NumIndices += m_Topology.GetNumPoints();
+    }
+
+    return NumIndices;
+}
+
 template <typename T>
 pxr::VtValue ConvertVertexArrayToFaceVaryingArray(const pxr::VtIntArray& FaceVertexIndices, const pxr::VtArray<T>& VertexArray, size_t ValuesPerVertex)
 {