Add mesh index buffer optimization based on meshoptimizer library

Work similar to existing impl but yields better results with even less overdraw.

Source/Engine/Graphics/Models/ModelData.Tool.cpp

@@ -10,11 +10,12 @@
 #include "Engine/Core/Collections/BitArray.h"
 #include "Engine/Tools/ModelTool/ModelTool.h"
 #include "Engine/Tools/ModelTool/VertexTriangleAdjacency.h"
-#include "Engine/Profiler/ProfilerCPU.h"
 #include "Engine/Platform/Platform.h"
 #include "Engine/Platform/MessageBox.h"
+#include "Engine/Profiler/ProfilerCPU.h"
+#include <ThirdParty/meshoptimizer/meshoptimizer.h>
 #define USE_MIKKTSPACE 1
-#include "ThirdParty/MikkTSpace/mikktspace.h"
+#include <ThirdParty/MikkTSpace/mikktspace.h>
 #if USE_ASSIMP
 #define USE_SPATIAL_SORT 1
 #define ASSIMP_BUILD_NO_EXPORT
@@ -25,6 +26,26 @@
 #endif
 #include <stack>
 
+bool InitedMeshOpt = false;
+
+void* MeshOptAllocate(size_t size)
+{
+    return Allocator::Allocate(size);
+}
+
+void MeshOptDeallocate(void* ptr)
+{
+    Allocator::Free(ptr);
+}
+
+void InitMeshOpt()
+{
+    if (InitedMeshOpt)
+        return;
+    InitedMeshOpt = true;
+    meshopt_setAllocator(MeshOptAllocate, MeshOptDeallocate);
+}
+
 #if PLATFORM_WINDOWS
 
 // Import UVAtlas library
@@ -934,6 +955,23 @@ void MeshData::ImproveCacheLocality()
         LOG(Info, "Generated {3} for mesh in {0}s ({1} vertices, {2} indices)", time, vertexCount, indexCount, TEXT("optimized indices"));
 }
 
+void MeshData::Optimize()
+{
+    if (Indices.IsEmpty() || Positions.IsEmpty())
+        return;
+    PROFILE_CPU();
+    InitMeshOpt();
+
+    // Vertex cache optimization (https://meshoptimizer.org/#vertex-cache-optimization)
+    Array<uint32> tmpIndices;
+    tmpIndices.Resize(Indices.Count());
+    meshopt_optimizeVertexCache(tmpIndices.Get(), Indices.Get(), Indices.Count(), Positions.Count());
+
+    // Overdraw optimization (https://meshoptimizer.org/#overdraw-optimization)
+    const float overdrawThreshold = 1.05f;
+    meshopt_optimizeOverdraw(Indices.Get(), tmpIndices.Get(), Indices.Count(), (const float*)Positions.Get(), Positions.Count(), sizeof(Float3), overdrawThreshold);
+}
+
 float MeshData::CalculateTrianglesArea() const
 {
     PROFILE_CPU();