Disable line strip on OpenGL

On WebGL/MacOS the presence of restart index in the buffer causes
disastrous performance degradation

Author: TheMostDiligent

Hydrogent/interface/HnMesh.hpp

@@ -227,7 +227,7 @@ class HnMesh final : public pxr::HdMesh
         Uint32 NumIndices = 0;
     };
 
-    void UpdateIndexData(StagingIndexData& StagingInds, const pxr::VtValue& Points);
+    void UpdateIndexData(StagingIndexData& StagingInds, const pxr::VtValue& Points, bool UseStripTopology);
 
     void UpdateTopology(pxr::HdSceneDelegate& SceneDelegate,
                         pxr::HdRenderParam*   RenderParam,

Hydrogent/interface/HnRenderDelegate.hpp

@@ -422,6 +422,8 @@ class HnRenderDelegate final : public pxr::HdRenderDelegate
 
     HnMaterial* GetFallbackMaterial() const { return m_FallbackMaterial; }
 
+    bool AllowPrimitiveRestart() const;
+
 private:
     static const pxr::TfTokenVector SupportedRPrimTypes;
     static const pxr::TfTokenVector SupportedSPrimTypes;

Hydrogent/interface/HnRenderPass.hpp

@@ -195,7 +195,7 @@ class HnRenderPass final : public pxr::HdRenderPass
 
     void RenderPendingDrawItems(RenderState& State);
 
-    GraphicsPipelineDesc GetGraphicsDesc(const HnRenderPassState& RPState) const;
+    GraphicsPipelineDesc GetGraphicsDesc(const HnRenderPassState& RPState, bool UseStripTopology) const;
 
 private:
     HnRenderPassParams m_Params;

Hydrogent/src/HnMesh.cpp

@@ -430,7 +430,7 @@ void HnMesh::UpdateRepr(pxr::HdSceneDelegate& SceneDelegate,
     if (IndexDataDirty && m_VertexHandle)
     {
         StagingIndexData StagingInds;
-        UpdateIndexData(StagingInds, StagingVerts.Points);
+        UpdateIndexData(StagingInds, StagingVerts.Points, RenderDelegate->AllowPrimitiveRestart());
 
         HnGeometryPool& GeometryPool = RenderDelegate->GetGeometryPool();
 
@@ -1064,7 +1064,7 @@ void HnMesh::GenerateSmoothNormals(HnRenderDelegate& RenderDelegate, StagingVert
     AddStagingBufferSourceForPrimvar(&RenderDelegate, StagingVerts, pxr::HdTokens->normals, pxr::VtValue::Take(Normals), pxr::HdInterpolationVertex);
 }
 
-void HnMesh::UpdateIndexData(StagingIndexData& StagingInds, const pxr::VtValue& Points)
+void HnMesh::UpdateIndexData(StagingIndexData& StagingInds, const pxr::VtValue& Points, bool UseStripTopology)
 {
     HnMeshUtils     MeshUtils{m_Topology, GetId()};
     pxr::VtIntArray SubsetStart;
@@ -1085,7 +1085,7 @@ void HnMesh::UpdateIndexData(StagingIndexData& StagingInds, const pxr::VtValue&
         m_IndexData.Subsets.clear();
     }
 
-    StagingInds.EdgeIndices  = MeshUtils.ComputeEdgeIndices(!m_HasFaceVaryingPrimvars, true);
+    StagingInds.EdgeIndices  = MeshUtils.ComputeEdgeIndices(!m_HasFaceVaryingPrimvars, UseStripTopology);
     StagingInds.PointIndices = MeshUtils.ComputePointIndices(m_HasFaceVaryingPrimvars);
 }
 
@@ -1154,7 +1154,7 @@ void HnMesh::UpdateDrawItemGpuTopology(HnRenderDelegate& RenderDelegate)
                 DrawItem.SetFaces({});
             }
 
-            // Render edgesand points for the entire mesh at once
+            // Render edges and points for the entire mesh at once
             DrawItem.SetEdges({
                 m_IndexData.Edges->GetBuffer(),
                 m_IndexData.Edges->GetStartIndex(),

Hydrogent/src/HnRenderDelegate.cpp

@@ -899,6 +899,13 @@ IShaderResourceBinding* HnRenderDelegate::GetShadowPassFrameAttribsSRB(Uint32 Li
     return m_ShadowPassFrameAttribs.SRB;
 }
 
+bool HnRenderDelegate::AllowPrimitiveRestart() const
+{
+    // WebGL supports primitive restart index, however on MacOS the presence of the restart index
+    // in the buffer causes disastrous performance degradation. So we disable it on OpenGL.
+    return !m_pDevice->GetDeviceInfo().IsGLDevice();
+}
+
 } // namespace USD
 
 } // namespace Diligent

Hydrogent/src/HnRenderPass.cpp

@@ -198,7 +198,7 @@ struct HnRenderPass::RenderState
     {
         if (!PsoCache)
         {
-            GraphicsPipelineDesc GraphicsDesc = RenderPass.GetGraphicsDesc(RPState);
+            GraphicsPipelineDesc GraphicsDesc = RenderPass.GetGraphicsDesc(RPState, RenderDelegate.AllowPrimitiveRestart());
 
             PsoCache = USDRenderer.GetPsoCacheAccessor(GraphicsDesc);
             VERIFY_EXPR(PsoCache);
@@ -220,7 +220,7 @@ struct HnRenderPass::RenderState
     USD_Renderer::PsoCacheAccessor PsoCache;
 };
 
-GraphicsPipelineDesc HnRenderPass::GetGraphicsDesc(const HnRenderPassState& RPState) const
+GraphicsPipelineDesc HnRenderPass::GetGraphicsDesc(const HnRenderPassState& RPState, bool UseStripTopology) const
 {
     GraphicsPipelineDesc GraphicsDesc = RPState.GetGraphicsPipelineDesc();
     if ((m_Params.UsdPsoFlags & USD_Renderer::USD_PSO_FLAG_ENABLE_ALL_OUTPUTS) == 0)
@@ -237,7 +237,7 @@ GraphicsPipelineDesc HnRenderPass::GetGraphicsDesc(const HnRenderPassState& RPSt
             break;
 
         case HN_RENDER_MODE_MESH_EDGES:
-            GraphicsDesc.PrimitiveTopology = PRIMITIVE_TOPOLOGY_LINE_STRIP;
+            GraphicsDesc.PrimitiveTopology = UseStripTopology ? PRIMITIVE_TOPOLOGY_LINE_STRIP : PRIMITIVE_TOPOLOGY_LINE_LIST;
             break;
 
         case HN_RENDER_MODE_POINTS: