From d9a2cd67d1e59a4703ed3edc1610bb270516dd78 Mon Sep 17 00:00:00 2001
From: assiduous <assiduous@diligentgraphics.com>
Date: Sat, 5 Oct 2024 11:27:53 -0700
Subject: [PATCH] HnGeometryPool: added option to disallow pool allocation
 reuse to support GL

---
 Hydrogent/interface/HnGeometryPool.hpp |  3 ++-
 Hydrogent/src/HnGeometryPool.cpp       | 16 ++++++++++------
 Hydrogent/src/HnMesh.cpp               |  5 ++++-
 3 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/Hydrogent/interface/HnGeometryPool.hpp b/Hydrogent/interface/HnGeometryPool.hpp
index 83f9beb4..a8c718f8 100644
--- a/Hydrogent/interface/HnGeometryPool.hpp
+++ b/Hydrogent/interface/HnGeometryPool.hpp
@@ -85,7 +85,8 @@ class HnGeometryPool final
 
     void AllocateVertices(const std::string&             Name,
                           const BufferSourcesMapType&    Sources,
-                          std::shared_ptr<VertexHandle>& Handle);
+                          std::shared_ptr<VertexHandle>& Handle,
+                          bool                           DisallowPoolAllocationReuse);
 
     void AllocateIndices(const std::string&                            Name,
                          pxr::VtValue                                  Indices,
diff --git a/Hydrogent/src/HnGeometryPool.cpp b/Hydrogent/src/HnGeometryPool.cpp
index 0f83549a..72d4894a 100644
--- a/Hydrogent/src/HnGeometryPool.cpp
+++ b/Hydrogent/src/HnGeometryPool.cpp
@@ -118,6 +118,7 @@ class HnGeometryPool::VertexData final : public GeometryPoolData
                const BufferSourcesMapType&   Sources,
                const VertexStreamHashesType& Hashes,
                GLTF::ResourceManager*        pResMgr,
+               bool                          DisallowPoolAllocationReuse,
                std::shared_ptr<VertexData>   ExistingData) :
         m_Name{std::move(Name)},
         m_NumVertices{!Sources.empty() ? static_cast<Uint32>(Sources.begin()->second->GetNumElements()) : 0},
@@ -194,7 +195,7 @@ class HnGeometryPool::VertexData final : public GeometryPoolData
 
         // If there is existing data, we will check if it is not used by other
         // handles in the Update() method and hence its buffers can be reused.
-        if (!ExistingData)
+        if (!ExistingData || DisallowPoolAllocationReuse)
         {
             InitPoolAllocation();
         }
@@ -226,7 +227,7 @@ class HnGeometryPool::VertexData final : public GeometryPoolData
         }
 
         std::shared_ptr<VertexData>& ExistingData = m_StagingData->ExistingData;
-        if (ExistingData)
+        if (ExistingData && !m_PoolAllocation)
         {
             if (ExistingData->GetUseCount() == 0)
             {
@@ -456,8 +457,8 @@ class HnGeometryPool::VertexData final : public GeometryPoolData
 
         std::shared_ptr<VertexData> ExistingData;
 
-        StagingData(GLTF::ResourceManager* pResMgr) :
-            pResMgr{pResMgr}
+        StagingData(GLTF::ResourceManager* _pResMgr) :
+            pResMgr{_pResMgr}
         {}
     };
     std::unique_ptr<StagingData> m_StagingData;
@@ -813,7 +814,8 @@ class HnGeometryPool::IndexHandleImpl final : public HnGeometryPool::IndexHandle
 
 void HnGeometryPool::AllocateVertices(const std::string&             Name,
                                       const BufferSourcesMapType&    Sources,
-                                      std::shared_ptr<VertexHandle>& Handle)
+                                      std::shared_ptr<VertexHandle>& Handle,
+                                      bool                           DisallowPoolAllocationReuse)
 {
     if (Sources.empty())
     {
@@ -845,7 +847,9 @@ void HnGeometryPool::AllocateVertices(const std::string&             Name,
         [&]() {
             // This code is executed only if the data is not found in the cache, and the data is created only once.
 
-            std::shared_ptr<VertexData> Data = std::make_shared<VertexData>(Name, Sources, Hashes, m_UseVertexPool ? &m_ResMgr : nullptr, ExistingData);
+            std::shared_ptr<VertexData> Data = std::make_shared<VertexData>(Name, Sources, Hashes,
+                                                                            m_UseVertexPool ? &m_ResMgr : nullptr,
+                                                                            DisallowPoolAllocationReuse, ExistingData);
 
             {
                 std::lock_guard<std::mutex> Guard{m_PendingVertexDataMtx};
diff --git a/Hydrogent/src/HnMesh.cpp b/Hydrogent/src/HnMesh.cpp
index 2c98fc2c..a160e96f 100644
--- a/Hydrogent/src/HnMesh.cpp
+++ b/Hydrogent/src/HnMesh.cpp
@@ -393,7 +393,10 @@ void HnMesh::UpdateRepr(pxr::HdSceneDelegate& SceneDelegate,
     if (!StagingVerts.Sources.empty())
     {
         HnGeometryPool& GeometryPool = RenderDelegate->GetGeometryPool();
-        GeometryPool.AllocateVertices(Id.GetString(), StagingVerts.Sources, m_VertexHandle);
+        // When native start vertex is not supported, start vertex needs to be baked into the index data, and
+        // we need to know the start vertex now, so we have to disallow pool allocation reuse (with pool allocation reuse
+        // enabled, the allocation initialization is delayed until the GeometryPool.Commit() is called later).
+        GeometryPool.AllocateVertices(Id.GetString(), StagingVerts.Sources, m_VertexHandle, /*DisallowPoolAllocationReuse = */ !UseNativeStartVertex);
 
         if (!UseNativeStartVertex)
         {