From 248304a78f3ded68bc05e2cc0b488e02619f54a5 Mon Sep 17 00:00:00 2001
From: Wojtek Figat <wojtek@figat.pl>
Date: Fri, 22 Sep 2023 19:43:00 +0200
Subject: [PATCH] Fix regression of importing only a single material for models
 with split objects enabled

#1483
---
 .../Tools/ModelTool/ModelTool.Assimp.cpp       |  7 ++++++-
 .../Tools/ModelTool/ModelTool.OpenFBX.cpp      | 18 ++++++++++++++++--
 Source/Engine/Tools/ModelTool/ModelTool.cpp    |  4 ----
 3 files changed, 22 insertions(+), 7 deletions(-)

diff --git a/Source/Engine/Tools/ModelTool/ModelTool.Assimp.cpp b/Source/Engine/Tools/ModelTool/ModelTool.Assimp.cpp
index ab9b6b606..7eff75514 100644
--- a/Source/Engine/Tools/ModelTool/ModelTool.Assimp.cpp
+++ b/Source/Engine/Tools/ModelTool/ModelTool.Assimp.cpp
@@ -566,12 +566,17 @@ bool ImportMaterials(ImportedModelData& result, AssimpImporterData& data, String
     return false;
 }
 
+bool IsMeshInvalid(const aiMesh* aMesh)
+{
+    return aMesh->mPrimitiveTypes != aiPrimitiveType_TRIANGLE || aMesh->mNumVertices == 0 || aMesh->mNumFaces == 0 || aMesh->mFaces[0].mNumIndices != 3;
+}
+
 bool ImportMesh(int32 i, ImportedModelData& result, AssimpImporterData& data, String& errorMsg)
 {
     const auto aMesh = data.Scene->mMeshes[i];
 
     // Skip invalid meshes
-    if (aMesh->mPrimitiveTypes != aiPrimitiveType_TRIANGLE || aMesh->mNumVertices == 0 || aMesh->mNumFaces == 0 || aMesh->mFaces[0].mNumIndices != 3)
+    if (IsMeshInvalid(aMesh))
         return false;
 
     // Skip unused meshes
diff --git a/Source/Engine/Tools/ModelTool/ModelTool.OpenFBX.cpp b/Source/Engine/Tools/ModelTool/ModelTool.OpenFBX.cpp
index ab55df7f6..215eadaba 100644
--- a/Source/Engine/Tools/ModelTool/ModelTool.OpenFBX.cpp
+++ b/Source/Engine/Tools/ModelTool/ModelTool.OpenFBX.cpp
@@ -923,8 +923,6 @@ bool ImportMesh(int32 index, ImportedModelData& result, OpenFbxImporterData& dat
     const auto aMesh = data.Scene->getMesh(index);
     const auto aGeometry = aMesh->getGeometry();
     const auto trianglesCount = aGeometry->getVertexCount() / 3;
-
-    // Skip invalid meshes
     if (IsMeshInvalid(aMesh))
         return false;
 
@@ -1272,6 +1270,22 @@ bool ModelTool::ImportDataOpenFBX(const char* path, ImportedModelData& data, Opt
             const auto meshIndex = Math::Clamp<int32>(options.ObjectIndex, 0, meshCount - 1);
             if (ImportMesh(meshIndex, data, *context, errorMsg))
                 return true;
+
+            // Let the firstly imported mesh import all materials from all meshes (index 0 is importing all following ones before itself during splitting - see code above)
+            if (options.ObjectIndex == 1)
+            {
+                for (int32 i = 0; i < meshCount; i++)
+                {
+                    const auto aMesh = context->Scene->getMesh(i);
+                    if (i == 1 || IsMeshInvalid(aMesh))
+                        continue;
+                    for (int32 j = 0; j < aMesh->getMaterialCount(); j++)
+                    {
+                        const ofbx::Material* aMaterial = aMesh->getMaterial(j);
+                        context->AddMaterial(data, aMaterial);
+                    }
+                }
+            }
         }
         else
         {
diff --git a/Source/Engine/Tools/ModelTool/ModelTool.cpp b/Source/Engine/Tools/ModelTool/ModelTool.cpp
index 99873c016..15c7cbc32 100644
--- a/Source/Engine/Tools/ModelTool/ModelTool.cpp
+++ b/Source/Engine/Tools/ModelTool/ModelTool.cpp
@@ -910,10 +910,6 @@ bool ModelTool::ImportModel(const String& path, ModelData& meshData, Options& op
     {
         auto& texture = data.Textures[i];
 
-        // When splitting imported meshes allow only the first mesh to import assets (mesh[0] is imported after all following ones so import assets during mesh[1])
-        if (!options.SplitObjects && options.ObjectIndex != 1 && options.ObjectIndex != -1)
-            continue;
-
         // Auto-import textures
         if (autoImportOutput.IsEmpty() || (data.Types & ImportDataTypes::Textures) == ImportDataTypes::None || texture.FilePath.IsEmpty())
             continue;