Merge remote-tracking branch 'origin/master' into 1.13

# Conflicts:
#	Content/Shaders/Editor/Grid.flax
#	Content/Shaders/GBuffer.flax
#	Content/Shaders/GlobalSignDistanceField.flax
#	Content/Shaders/ProbesFilter.flax
#	Content/Shaders/SSR.flax
#	Content/Shaders/VolumetricFog.flax
#	Development/Documentation/mono.md
#	Source/Editor/Modules/ContentDatabaseModule.cs

Source/Engine/Content/Storage/ContentStorageManager.cpp

@@ -122,11 +122,8 @@ FlaxStorageReference ContentStorageManager::EnsureAccess(const StringView& path)
     // Note: because we want to create new storage package it may exists.
     // So let's check if any storage container is referencing that location and try to close it.
     auto storage = TryGetStorage(path);
-    if (storage && storage->IsLoaded())
-    {
-        LOG(Info, "File \'{0}\' is in use. Trying to release handle to it.", path);
-        storage->CloseFileHandles();
-    }
+    if (storage && storage->IsLoaded() && storage->CloseFileHandles())
+        LOG(Warning, "Cannot release content storage handle for '{0}'.", path);
     return storage;
 }
 

Source/Engine/Content/Storage/FlaxStorage.cpp

@@ -1438,10 +1438,6 @@ FileReadStream* FlaxStorage::OpenFile()
 
 bool FlaxStorage::CloseFileHandles()
 {
-    // Guard the whole process so if new thread wants to lock the chunks will need to wait for this to end
-    Platform::InterlockedIncrement(&_isUnloadingData);
-    SCOPE_EXIT{ Platform::InterlockedDecrement(&_isUnloadingData); };
-
     if (Platform::AtomicRead(&_chunksLock) == 0 && Platform::AtomicRead(&_files) == 0)
         return false; // Early out when no files are opened
     PROFILE_CPU();
@@ -1469,7 +1465,13 @@ bool FlaxStorage::CloseFileHandles()
             }
         }
     }
-    waitTime = 100;
+
+    // Guard the whole process so if new thread wants to lock the chunks will need to wait for this to end
+    Platform::InterlockedIncrement(&_isUnloadingData);
+    SCOPE_EXIT{ Platform::InterlockedDecrement(&_isUnloadingData); };
+
+    // Wait for chunks lock again (with larger timeout for longer tasks)
+    waitTime = 1000;
     while (Platform::AtomicRead(&_chunksLock) != 0 && waitTime-- > 0)
         Platform::Sleep(1);
     if (Platform::AtomicRead(&_chunksLock) != 0)

Source/Engine/Engine/NativeInterop.Unmanaged.cs

@@ -901,20 +901,21 @@ namespace FlaxEngine.Interop
 
                 Assembly assembly;
 #if FLAX_EDITOR
-                // Load assembly from loaded bytes to prevent file locking in Editor
-                var assemblyBytes = File.ReadAllBytes(assemblyPath);
-                using MemoryStream stream = new MemoryStream(assemblyBytes);
+                // Load assembly with stream to prevent runtime from locking the assembly file
+                using FileStream stream = new FileStream(assemblyPath, FileMode.Open, FileAccess.Read);
                 var pdbPath = Path.ChangeExtension(assemblyPath, "pdb");
                 if (File.Exists(pdbPath))
                 {
                     // Load including debug symbols
-                    using FileStream pdbStream = new FileStream(Path.ChangeExtension(assemblyPath, "pdb"), FileMode.Open);
+                    using FileStream pdbStream = new FileStream(Path.ChangeExtension(assemblyPath, "pdb"), FileMode.Open, FileAccess.Read);
                     assembly = scriptingAssemblyLoadContext.LoadFromStream(stream, pdbStream);
                 }
                 else
                 {
                     assembly = scriptingAssemblyLoadContext.LoadFromStream(stream);
                 }
+
+                // TODO: Use new .NET 11 AssemblyLoadContext.SetAssemblyLocationOverride to specify correct Assembly.Location
 #else
                 // Load assembly from file
                 assembly = scriptingAssemblyLoadContext.LoadFromAssemblyPath(assemblyPath);

Source/Engine/Graphics/Models/Mesh.cpp

@@ -197,7 +197,7 @@ bool Mesh::UpdateMesh(uint32 vertexCount, uint32 triangleCount, const Float3* ve
 
 bool Mesh::UpdateMesh(uint32 vertexCount, uint32 triangleCount, const Float3* vertices, const uint32* triangles, const Float3* normals, const Float3* tangents, const Float2* uvs, const Color32* colors)
 {
-    return ::UpdateMesh(this, vertexCount, triangleCount, PixelFormat::R16_UInt, vertices, triangles, normals, tangents, uvs, colors);
+    return ::UpdateMesh(this, vertexCount, triangleCount, PixelFormat::R32_UInt, vertices, triangles, normals, tangents, uvs, colors);
 }
 
 bool Mesh::Load(uint32 vertices, uint32 triangles, const void* vb0, const void* vb1, const void* vb2, const void* ib, bool use16BitIndexBuffer)

Source/Engine/Graphics/Models/SkinnedMesh.cpp

@@ -305,7 +305,7 @@ bool SkinnedMesh::UpdateMesh(uint32 vertexCount, uint32 triangleCount, const Flo
 
 bool SkinnedMesh::UpdateMesh(uint32 vertexCount, uint32 triangleCount, const Float3* vertices, const uint32* triangles, const Int4* blendIndices, const Float4* blendWeights, const Float3* normals, const Float3* tangents, const Float2* uvs, const Color32* colors)
 {
-    return ::UpdateMesh(this, vertexCount, triangleCount, PixelFormat::R16_UInt, vertices, triangles, blendIndices, blendWeights, normals, tangents, uvs, colors);
+    return ::UpdateMesh(this, vertexCount, triangleCount, PixelFormat::R32_UInt, vertices, triangles, blendIndices, blendWeights, normals, tangents, uvs, colors);
 }
 
 void SkinnedMesh::Draw(const RenderContext& renderContext, const SkinnedMeshBones& pose, MaterialBase* material, const Matrix& world, StaticFlags flags, bool receiveDecals, DrawPass drawModes, float perInstanceRandom, int8 sortOrder, uint8 stencilValue) const

Source/Engine/Platform/Base/Enums.h

@@ -28,6 +28,11 @@ API_ENUM() enum class ClosingReason
     /// The close event.
     /// </summary>
     CloseEvent,
+    
+    /// <summary>
+    /// The scripts reload event.
+    /// </summary>
+    ScriptsReload,
 };
 
 /// <summary>

Source/Engine/ShadersCompilation/ShadersCompilation.cpp

@@ -26,6 +26,8 @@
 #if USE_EDITOR
 #define COMPILE_WITH_ASSETS_IMPORTER 1 // Hack to use shaders importing in this module
 #include "Engine/ContentImporters/AssetsImportingManager.h"
+#include "Engine/Content/Storage/ContentStorageManager.h"
+#include "Engine/Utilities/Encryption.h"
 #include "Engine/Platform/FileSystemWatcher.h"
 #include "Engine/Platform/FileSystem.h"
 #include "Engine/Platform/File.h"
@@ -499,6 +501,37 @@ String ShadersCompilation::CompactShaderPath(StringView path)
 
 #if USE_EDITOR
 
+bool ShadersCompilation::IsShaderSourceAssetUpToDate(const StringView& sourcePath, const StringView& assetPath)
+{
+    PROFILE_CPU();
+    StringAnsi source;
+    if (File::ReadAllText(sourcePath, source))
+        return false;
+    if (!source.HasChars() || source[source.Length() - 1] != '\n')
+        source.Append('\n');
+
+    const auto storage = ContentStorageManager::GetStorage(assetPath);
+    AssetInitData data;
+    if (!storage
+        || storage->GetEntriesCount() != 1
+        || storage->GetEntry(0).TypeName != Shader::TypeName
+        || storage->LoadAssetHeader(0, data)
+        || data.SerializedVersion != Shader::SerializedVersion)
+        return false;
+
+    FlaxChunk* sourceChunk = data.Header.Chunks[SHADER_FILE_CHUNK_SOURCE];
+    if (!sourceChunk || storage->LoadAssetChunk(sourceChunk) || !sourceChunk->Data.IsValid())
+        return false;
+
+    BytesContainer embeddedSource;
+    embeddedSource.Copy(sourceChunk->Data);
+    if (embeddedSource.Length() != source.Length() + 1)
+        return false;
+    Encryption::DecryptBytes(embeddedSource.Get(), embeddedSource.Length());
+    embeddedSource.Get()[embeddedSource.Length() - 1] = 0;
+    return Platform::MemoryCompare(embeddedSource.Get(), source.Get(), source.Length()) == 0;
+}
+
 namespace
 {
     Array<FileSystemWatcher*> ShadersSourcesWatchers;
@@ -515,6 +548,13 @@ namespace
         return result;
     }
 
+    bool ImportShaderIfChanged(const StringView& sourcePath, const StringView& assetPath, Guid& assetId)
+    {
+        if (ShadersCompilation::IsShaderSourceAssetUpToDate(sourcePath, assetPath))
+            return false;
+        return AssetsImportingManager::Import(sourcePath, assetPath, assetId);
+    }
+
     void OnWatcherShadersEvent(const String& path, FileSystemAction action)
     {
         if (action == FileSystemAction::Delete || !path.EndsWith(TEXT(".shader")))
@@ -538,7 +578,7 @@ namespace
         const String name = StringUtils::GetPathWithoutExtension(localPath);
         const String outputPath = shadersAssetsPath / name + ASSET_FILES_EXTENSION_WITH_DOT;
         Guid id = GetShaderAssetId(name);
-        AssetsImportingManager::ImportIfEdited(path, outputPath, id);
+        ImportShaderIfChanged(path, outputPath, id);
     }
 
     void RegisterShaderWatchers(const ProjectInfo* project, HashSet<const ProjectInfo*>& projects)
@@ -567,7 +607,7 @@ namespace
                 const String name = StringUtils::GetPathWithoutExtension(localPath);
                 const String outputPath = shadersAssetsPath / name + ASSET_FILES_EXTENSION_WITH_DOT;
                 Guid id = GetShaderAssetId(name);
-                AssetsImportingManager::ImportIfEdited(path, outputPath, id);
+                ImportShaderIfChanged(path, outputPath, id);
             }
         }
 

Source/Engine/ShadersCompilation/ShadersCompilation.h

@@ -47,6 +47,16 @@ public:
     // Compacts the full shader file path into portable format with project name prefix such as './<ProjectName>/ShaderFile.hlsl'.
     static String CompactShaderPath(StringView path);
 
+#if USE_EDITOR
+    /// <summary>
+    /// Checks whether a shader asset embeds the current source file contents.
+    /// </summary>
+    /// <param name="sourcePath">The shader source file path.</param>
+    /// <param name="assetPath">The shader asset file path.</param>
+    /// <returns>True when the embedded source matches, otherwise false.</returns>
+    static bool IsShaderSourceAssetUpToDate(const StringView& sourcePath, const StringView& assetPath);
+#endif
+
 private:
     static ShaderCompiler* RequestCompiler(ShaderProfile profile, PlatformType platform);
     static void FreeCompiler(ShaderCompiler* compiler);

Source/Engine/Tests/TestContainerControl.cs

@@ -26,6 +26,29 @@ namespace FlaxEngine.Tests
             }
         }
 
+        private sealed class RemovingControl : MyControl
+        {
+            private readonly Control[] _controlsToRemove;
+
+            public RemovingControl(float x, float y, float width, float height, params Control[] controlsToRemove)
+            : base(x, y, width, height)
+            {
+                _controlsToRemove = controlsToRemove;
+            }
+
+            public override void OnMouseEnter(Float2 location)
+            {
+                for (int i = 0; i < _controlsToRemove.Length; i++)
+                {
+                    var control = _controlsToRemove[i];
+                    if (control.Parent == Parent)
+                        control.Parent = null;
+                }
+
+                base.OnMouseEnter(location);
+            }
+        }
+
         [Test]
         public void TestChildren()
         {
@@ -53,6 +76,25 @@ namespace FlaxEngine.Tests
             Assert.AreEqual(cc1.GetChildAt(new Vector2(15, 5)), cc2);
             Assert.AreEqual(cc1.GetChildAtRecursive(new Vector2(35, 25)), c3);
         }
+
+        [Test]
+        public void TestMouseMoveAllowsChildrenRemoval()
+        {
+            var container = new MyContainerControl(0, 0, 100, 100);
+            var first = new MyControl(0, 0, 100, 100);
+            var second = new MyControl(0, 0, 100, 100);
+            var removing = new RemovingControl(0, 0, 100, 100, first, second);
+            container.AddChild(first);
+            container.AddChild(second);
+            container.AddChild(removing);
+
+            // The top-most child removes multiple siblings during input dispatch.
+            // Traversal must not use the now-stale next index.
+            container.OnMouseMove(new Float2(50, 50));
+
+            Assert.AreEqual(1, container.ChildrenCount);
+            Assert.AreEqual(removing, container.GetChild(0));
+        }
     }
 }
 #endif

Source/Engine/Tests/TestShaderSourceSync.cpp

@@ -0,0 +1,42 @@
+// Copyright (c) Wojciech Figat. All rights reserved.
+
+#include "Engine/Core/ScopeExit.h"
+#include "Engine/Core/Types/DataContainer.h"
+#include "Engine/Engine/Globals.h"
+#include "Engine/Platform/File.h"
+#include "Engine/Platform/FileSystem.h"
+#include "Engine/ShadersCompilation/ShadersCompilation.h"
+#include <ThirdParty/catch2/catch.hpp>
+
+#if COMPILE_WITH_SHADER_COMPILER && USE_EDITOR
+
+TEST_CASE("Shader source asset synchronization ignores timestamps")
+{
+    const String sourcePath = Globals::StartupFolder / TEXT("Source/Shaders/VolumetricFog.shader");
+    const String assetPath = Globals::EngineContentFolder / TEXT("Shaders/VolumetricFog.flax");
+    REQUIRE(FileSystem::FileExists(sourcePath));
+    REQUIRE(FileSystem::FileExists(assetPath));
+    CHECK(ShadersCompilation::IsShaderSourceAssetUpToDate(sourcePath, assetPath));
+
+    const String tempRoot = Globals::TemporaryFolder / (TEXT("ShaderSourceSync-") + Guid::New().ToString(Guid::FormatType::N));
+    REQUIRE(!FileSystem::CreateDirectory(tempRoot));
+    SCOPE_EXIT
+    {
+        FileSystem::DeleteDirectory(tempRoot, true);
+    };
+
+    DataContainer<byte> assetData;
+    StringAnsi modifiedSource;
+    REQUIRE(!File::ReadAllBytes(assetPath, assetData));
+    REQUIRE(!File::ReadAllText(sourcePath, modifiedSource));
+    modifiedSource.Append("// Deliberately different source\n");
+
+    const String tempSourcePath = tempRoot / TEXT("VolumetricFog.shader");
+    const String tempAssetPath = tempRoot / TEXT("VolumetricFog.flax");
+    REQUIRE(!File::WriteAllBytes(tempSourcePath, modifiedSource.Get(), modifiedSource.Length()));
+    REQUIRE(!File::WriteAllBytes(tempAssetPath, assetData.Get(), assetData.Length()));
+    CHECK_FALSE(FileSystem::GetFileLastEditTime(tempSourcePath) > FileSystem::GetFileLastEditTime(tempAssetPath));
+    CHECK_FALSE(ShadersCompilation::IsShaderSourceAssetUpToDate(tempSourcePath, tempAssetPath));
+}
+
+#endif

Source/Engine/Tests/Tests.Build.cs

@@ -21,6 +21,7 @@ public class Tests : EngineModule
         base.Setup(options);
 
         options.PrivateDependencies.Add("ModelTool");
+        options.PrivateDependencies.Add("ShadersCompilation");
     }
 
     /// <inheritdoc />

Source/Engine/Tools/ModelTool/ModelTool.Assimp.cpp

@@ -20,26 +20,29 @@
 #include <ThirdParty/assimp/scene.h>
 #include <ThirdParty/assimp/version.h>
 #include <ThirdParty/assimp/postprocess.h>
-#include <ThirdParty/assimp/LogStream.hpp>
 #include <ThirdParty/assimp/DefaultLogger.hpp>
 #include <ThirdParty/assimp/Logger.hpp>
 
-class AssimpLogStream : public Assimp::LogStream
+class AssimpLogger final : public Assimp::Logger
 {
 public:
-    AssimpLogStream()
+    AssimpLogger()
+        : Logger(NORMAL)
     {
-        Assimp::DefaultLogger::create("");
-        Assimp::DefaultLogger::get()->attachStream(this);
     }
 
-    ~AssimpLogStream()
+    bool attachStream(Assimp::LogStream*, unsigned int) override
     {
-        Assimp::DefaultLogger::get()->detachStream(this);
-        Assimp::DefaultLogger::kill();
+        return false;
     }
 
-    void write(const char* message) override
+    bool detachStream(Assimp::LogStream*, unsigned int) override
+    {
+        return false;
+    }
+
+private:
+    static void Write(const Char* type, const char* message)
     {
         String s(message);
         if (s.Length() <= 0)
@@ -52,10 +55,49 @@ public:
             else if (c >= 255)
                 c = '?';
         }
-        LOG(Info, "[Assimp]: {0}", s);
+        LOG(Info, "[Assimp]: {0}: {1}", type, s);
+    }
+
+    void OnDebug(const char* message) override
+    {
+        if (m_Severity >= DEBUGGING)
+            Write(TEXT("Debug"), message);
+    }
+
+    void OnVerboseDebug(const char* message) override
+    {
+        if (m_Severity >= VERBOSE)
+            Write(TEXT("Debug"), message);
+    }
+
+    void OnInfo(const char* message) override
+    {
+        Write(TEXT("Info"), message);
+    }
+
+    void OnWarn(const char* message) override
+    {
+        Write(TEXT("Warn"), message);
+    }
+
+    void OnError(const char* message) override
+    {
+        Write(TEXT("Error"), message);
     }
 };
 
+Assimp::Logger* GetAssimpLogger()
+{
+    static Assimp::Logger* logger = []()
+    {
+        auto result = new AssimpLogger();
+        Assimp::DefaultLogger::set(result);
+        LOG(Info, "Assimp {0}.{1}.{2}", aiGetVersionMajor(), aiGetVersionMinor(), aiGetVersionRevision());
+        return result;
+    }();
+    return logger;
+}
+
 Float2 ToFloat2(const aiVector2D& v)
 {
     return Float2(v.x, v.y);
@@ -148,7 +190,6 @@ struct AssimpBone
 struct AssimpImporterData
 {
     Assimp::Importer AssimpImporter;
-    AssimpLogStream AssimpLogStream;
     const String Path;
     const aiScene* Scene = nullptr;
     const ModelTool::Options& Options;
@@ -705,12 +746,7 @@ void ImportAnimation(int32 index, ModelData& data, AssimpImporterData& importerD
 
 bool ModelTool::ImportDataAssimp(const String& path, ModelData& data, Options& options, String& errorMsg)
 {
-    static bool AssimpInited = false;
-    if (!AssimpInited)
-    {
-        AssimpInited = true;
-        LOG(Info, "Assimp {0}.{1}.{2}", aiGetVersionMajor(), aiGetVersionMinor(), aiGetVersionRevision());
-    }
+    GetAssimpLogger();
     bool importMeshes = EnumHasAnyFlags(options.ImportTypes, ImportDataTypes::Geometry);
     bool importAnimations = EnumHasAnyFlags(options.ImportTypes, ImportDataTypes::Animations);
     AssimpImporterData context(path, options);

Source/Engine/UI/GUI/ContainerControl.cs

@@ -910,7 +910,7 @@ namespace FlaxEngine.GUI
                     return false;
                 }
             }
-            for (int i = _children.Count - 1; i >= 0 && _children.Count > 0; i--)
+            for (int i = _children.Count - 1; i >= 0 && i < _children.Count; i--)
             {
                 var child = _children[i];
                 if (child.Visible)
@@ -928,7 +928,7 @@ namespace FlaxEngine.GUI
         public override void OnMouseEnter(Float2 location)
         {
             // Check all children collisions with mouse and fire events for them
-            for (int i = _children.Count - 1; i >= 0 && _children.Count > 0; i--)
+            for (int i = _children.Count - 1; i >= 0 && i < _children.Count; i--)
             {
                 var child = _children[i];
                 if (child.Visible && child.Enabled)
@@ -948,7 +948,7 @@ namespace FlaxEngine.GUI
         public override void OnMouseMove(Float2 location)
         {
             // Check all children collisions with mouse and fire events for them
-            for (int i = _children.Count - 1; i >= 0 && _children.Count > 0; i--)
+            for (int i = _children.Count - 1; i >= 0 && i < _children.Count; i--)
             {
                 var child = _children[i];
                 if (child.Visible && child.Enabled)
@@ -998,7 +998,7 @@ namespace FlaxEngine.GUI
         public override bool OnMouseWheel(Float2 location, float delta)
         {
             // Check all children collisions with mouse and fire events for them
-            for (int i = _children.Count - 1; i >= 0 && _children.Count > 0; i--)
+            for (int i = _children.Count - 1; i >= 0 && i < _children.Count; i--)
             {
                 var child = _children[i];
                 if (child.Visible && child.Enabled)
@@ -1019,7 +1019,7 @@ namespace FlaxEngine.GUI
         public override bool OnMouseDown(Float2 location, MouseButton button)
         {
             // Check all children collisions with mouse and fire events for them
-            for (int i = _children.Count - 1; i >= 0 && _children.Count > 0; i--)
+            for (int i = _children.Count - 1; i >= 0 && i < _children.Count; i--)
             {
                 var child = _children[i];
                 if (child.Visible && child.Enabled)
@@ -1040,7 +1040,7 @@ namespace FlaxEngine.GUI
         public override bool OnMouseUp(Float2 location, MouseButton button)
         {
             // Check all children collisions with mouse and fire events for them
-            for (int i = _children.Count - 1; i >= 0 && _children.Count > 0; i--)
+            for (int i = _children.Count - 1; i >= 0 && i < _children.Count; i--)
             {
                 var child = _children[i];
                 if (child.Visible && child.Enabled)
@@ -1061,7 +1061,7 @@ namespace FlaxEngine.GUI
         public override bool OnMouseDoubleClick(Float2 location, MouseButton button)
         {
             // Check all children collisions with mouse and fire events for them
-            for (int i = _children.Count - 1; i >= 0 && _children.Count > 0; i--)
+            for (int i = _children.Count - 1; i >= 0 && i < _children.Count; i--)
             {
                 var child = _children[i];
                 if (child.Visible && child.Enabled)
@@ -1096,7 +1096,7 @@ namespace FlaxEngine.GUI
         /// <inheritdoc />
         public override void OnTouchEnter(Float2 location, int pointerId)
         {
-            for (int i = _children.Count - 1; i >= 0 && _children.Count > 0; i--)
+            for (int i = _children.Count - 1; i >= 0 && i < _children.Count; i--)
             {
                 var child = _children[i];
                 if (child.Visible && child.Enabled && !child.IsTouchPointerOver(pointerId))
@@ -1114,7 +1114,7 @@ namespace FlaxEngine.GUI
         /// <inheritdoc />
         public override bool OnTouchDown(Float2 location, int pointerId)
         {
-            for (int i = _children.Count - 1; i >= 0 && _children.Count > 0; i--)
+            for (int i = _children.Count - 1; i >= 0 && i < _children.Count; i--)
             {
                 var child = _children[i];
                 if (child.Visible && child.Enabled)
@@ -1139,7 +1139,7 @@ namespace FlaxEngine.GUI
         /// <inheritdoc />
         public override void OnTouchMove(Float2 location, int pointerId)
         {
-            for (int i = _children.Count - 1; i >= 0 && _children.Count > 0; i--)
+            for (int i = _children.Count - 1; i >= 0 && i < _children.Count; i--)
             {
                 var child = _children[i];
                 if (child.Visible && child.Enabled)
@@ -1168,7 +1168,7 @@ namespace FlaxEngine.GUI
         /// <inheritdoc />
         public override bool OnTouchUp(Float2 location, int pointerId)
         {
-            for (int i = _children.Count - 1; i >= 0 && _children.Count > 0; i--)
+            for (int i = _children.Count - 1; i >= 0 && i < _children.Count; i--)
             {
                 var child = _children[i];
                 if (child.Visible && child.Enabled && child.IsTouchPointerOver(pointerId))
@@ -1250,7 +1250,7 @@ namespace FlaxEngine.GUI
             var result = base.OnDragEnter(ref location, data);
 
             // Check all children collisions with mouse and fire events for them
-            for (int i = _children.Count - 1; i >= 0 && _children.Count > 0; i--)
+            for (int i = _children.Count - 1; i >= 0 && i < _children.Count; i--)
             {
                 var child = _children[i];
                 if (child.Visible && child.Enabled)
@@ -1275,7 +1275,7 @@ namespace FlaxEngine.GUI
             var result = base.OnDragMove(ref location, data);
 
             // Check all children collisions with mouse and fire events for them
-            for (int i = _children.Count - 1; i >= 0 && _children.Count > 0; i--)
+            for (int i = _children.Count - 1; i >= 0 && i < _children.Count; i--)
             {
                 var child = _children[i];
                 if (child.Visible && child.Enabled)
@@ -1333,7 +1333,7 @@ namespace FlaxEngine.GUI
             var result = base.OnDragDrop(ref location, data);
 
             // Check all children collisions with mouse and fire events for them
-            for (int i = _children.Count - 1; i >= 0 && _children.Count > 0; i--)
+            for (int i = _children.Count - 1; i >= 0 && i < _children.Count; i--)
             {
                 var child = _children[i];
                 if (child.Visible && child.Enabled)