Upgraded to ImGui 1.61:

- Upgraded ImGui framework to 1.61 WIP, which adds a few improvements to context management.
- Removed from plugin implementation all the references to default ImGui context.
- Removed from ImGui Context Proxy destructor code switching to default ImGui context (there is no default context and decision is left for a higher level manager when to switch and to what context).
- Added own font atlas that is shared by all contexts and used explicitly to create Slate resources.
- Removed from ImGui Context Proxy workaround that was previously needed for copying cursor data to dynamically created contexts.
- Removed explicit saving of context settings before its destruction as this is now handled in ImGui::DestroyContext().
- Reimplemented ImGuiImplementation::GetCursorData() to use new interface.

Source/ImGui/Private/ImGuiContextManager.cpp

@@ -79,8 +79,6 @@ FImGuiContextManager::~FImGuiContextManager()
 {
 	// Order matters because contexts can be created during World Tick Start events.
 	FWorldDelegates::OnWorldTickStart.RemoveAll(this);
-	Contexts.Empty();
-	ImGui::Shutdown();
 }
 
 void FImGuiContextManager::Tick(float DeltaSeconds)
@@ -118,7 +116,7 @@ FImGuiContextManager::FContextData& FImGuiContextManager::GetEditorContextData()
 
 	if (UNLIKELY(!Data))
 	{
-		Data = &Contexts.Emplace(Utilities::EDITOR_CONTEXT_INDEX, FContextData{ GetEditorContextName(), Utilities::EDITOR_CONTEXT_INDEX, DrawMultiContextEvent, ImGuiDemo, -1 });
+		Data = &Contexts.Emplace(Utilities::EDITOR_CONTEXT_INDEX, FContextData{ GetEditorContextName(), Utilities::EDITOR_CONTEXT_INDEX, DrawMultiContextEvent, FontAtlas, ImGuiDemo, -1 });
 	}
 
 	return *Data;
@@ -132,7 +130,7 @@ FImGuiContextManager::FContextData& FImGuiContextManager::GetStandaloneWorldCont
 
 	if (UNLIKELY(!Data))
 	{
-		Data = &Contexts.Emplace(Utilities::STANDALONE_GAME_CONTEXT_INDEX, FContextData{ GetWorldContextName(), Utilities::STANDALONE_GAME_CONTEXT_INDEX, DrawMultiContextEvent, ImGuiDemo });
+		Data = &Contexts.Emplace(Utilities::STANDALONE_GAME_CONTEXT_INDEX, FContextData{ GetWorldContextName(), Utilities::STANDALONE_GAME_CONTEXT_INDEX, DrawMultiContextEvent, FontAtlas, ImGuiDemo });
 	}
 
 	return *Data;
@@ -172,7 +170,7 @@ FImGuiContextManager::FContextData& FImGuiContextManager::GetWorldContextData(co
 #if WITH_EDITOR
 	if (UNLIKELY(!Data))
 	{
-		Data = &Contexts.Emplace(Index, FContextData{ GetWorldContextName(World), Index, DrawMultiContextEvent, ImGuiDemo, WorldContext->PIEInstance });
+		Data = &Contexts.Emplace(Index, FContextData{ GetWorldContextName(World), Index, DrawMultiContextEvent, FontAtlas, ImGuiDemo, WorldContext->PIEInstance });
 	}
 	else
 	{
@@ -182,7 +180,7 @@ FImGuiContextManager::FContextData& FImGuiContextManager::GetWorldContextData(co
 #else
 	if (UNLIKELY(!Data))
 	{
-		Data = &Contexts.Emplace(Index, FContextData{ GetWorldContextName(World), Index, DrawMultiContextEvent, ImGuiDemo });
+		Data = &Contexts.Emplace(Index, FContextData{ GetWorldContextName(World), Index, DrawMultiContextEvent, FontAtlas, ImGuiDemo });
 	}
 #endif
 

Source/ImGui/Private/ImGuiContextManager.h

@@ -21,6 +21,10 @@ class FImGuiContextManager
 
 	~FImGuiContextManager();
 
+	ImFontAtlas& GetFontAtlas() { return FontAtlas; }
+	const ImFontAtlas& GetFontAtlas() const { return FontAtlas; }
+
+
 #if WITH_EDITOR
 	// Get or create editor ImGui context proxy.
 	FORCEINLINE FImGuiContextProxy& GetEditorContextProxy() { return GetEditorContextData().ContextProxy; }
@@ -56,9 +60,9 @@ class FImGuiContextManager
 
 	struct FContextData
 	{
-		FContextData(const FString& ContextName, int32 ContextIndex, FSimpleMulticastDelegate& SharedDrawEvent, FImGuiDemo& Demo, int32 InPIEInstance = -1)
+		FContextData(const FString& ContextName, int32 ContextIndex, FSimpleMulticastDelegate& SharedDrawEvent, ImFontAtlas& FontAtlas, FImGuiDemo& Demo, int32 InPIEInstance = -1)
 			: PIEInstance(InPIEInstance)
-			, ContextProxy(ContextName, &SharedDrawEvent)
+			, ContextProxy(ContextName, &SharedDrawEvent, &FontAtlas)
 		{
 			ContextProxy.OnDraw().AddLambda([&Demo, ContextIndex]() { Demo.DrawControls(ContextIndex); });
 		}
@@ -73,8 +77,8 @@ class FImGuiContextManager
 
 	struct FContextData
 	{
-		FContextData(const FString& ContextName, int32 ContextIndex, FSimpleMulticastDelegate& SharedDrawEvent, FImGuiDemo& Demo)
-			: ContextProxy(ContextName, &SharedDrawEvent)
+		FContextData(const FString& ContextName, int32 ContextIndex, FSimpleMulticastDelegate& SharedDrawEvent, ImFontAtlas& FontAtlas, FImGuiDemo& Demo)
+			: ContextProxy(ContextName, &SharedDrawEvent, &FontAtlas)
 		{
 			ContextProxy.OnDraw().AddLambda([&Demo, ContextIndex]() { Demo.DrawControls(ContextIndex); });
 		}
@@ -103,4 +107,6 @@ class FImGuiContextManager
 	FImGuiDemo ImGuiDemo;
 
 	FSimpleMulticastDelegate DrawMultiContextEvent;
+
+	ImFontAtlas FontAtlas;
 };

Source/ImGui/Private/ImGuiContextProxy.cpp

@@ -44,13 +44,13 @@ namespace
 	}
 }
 
-FImGuiContextProxy::FImGuiContextProxy(const FString& InName, FSimpleMulticastDelegate* InSharedDrawEvent)
+FImGuiContextProxy::FImGuiContextProxy(const FString& InName, FSimpleMulticastDelegate* InSharedDrawEvent, ImFontAtlas* InFontAtlas)
 	: Name(InName)
 	, SharedDrawEvent(InSharedDrawEvent)
 	, IniFilename(TCHAR_TO_ANSI(*GetIniFile(InName)))
 {
 	// Create context.
-	Context = TUniquePtr<ImGuiContext>(ImGui::CreateContext());
+	Context = TUniquePtr<ImGuiContext>(ImGui::CreateContext(InFontAtlas));
 
 	// Set this context in ImGui for initialization (any allocations will be tracked in this context).
 	SetAsCurrent();
@@ -65,20 +65,6 @@ FImGuiContextProxy::FImGuiContextProxy(const FString& InName, FSimpleMulticastDe
 	IO.DisplaySize = { DEFAULT_CANVAS_WIDTH, DEFAULT_CANVAS_HEIGHT };
 	DisplaySize = ImGuiInterops::ToVector2D(IO.DisplaySize);
 
-	// When GetTexData is called for the first time it builds atlas texture and copies mouse cursor data to context.
-	// When multiple contexts share atlas then only the first one will get mouse data. A simple workaround is to use
-	// a temporary atlas if shared one is already built.
-	unsigned char* Pixels;
-	const bool bIsAltasBuilt = IO.Fonts->TexPixelsAlpha8 != nullptr;
-	if (bIsAltasBuilt)
-	{
-		ImFontAtlas().GetTexDataAsRGBA32(&Pixels, nullptr, nullptr);
-	}
-	else
-	{
-		IO.Fonts->GetTexDataAsRGBA32(&Pixels, nullptr, nullptr);
-	}
-
 	// Initialize key mapping, so context can correctly interpret input state.
 	ImGuiInterops::SetUnrealKeyMap(IO);
 
@@ -91,15 +77,12 @@ FImGuiContextProxy::~FImGuiContextProxy()
 {
 	if (Context)
 	{
-		// Set this context in ImGui for de-initialization (any de-allocations will be tracked in this context).
+		// Setting this as a current context is still required in the current framework version to properly shutdown
+		// and save data.
 		SetAsCurrent();
 
 		// Save context data and destroy.
-		ImGuiImplementation::SaveCurrentContextIniSettings(IniFilename.c_str());
 		ImGui::DestroyContext(Context.Release());
-
-		// Set default context in ImGui to keep global context pointer valid.
-		ImGui::SetCurrentContext(&ImGuiImplementation::GetDefaultContext());
 	}
 }
 

Source/ImGui/Private/ImGuiContextProxy.h

@@ -19,7 +19,7 @@ class FImGuiContextProxy
 {
 public:
 
-	FImGuiContextProxy(const FString& Name, FSimpleMulticastDelegate* InSharedDrawEvent);
+	FImGuiContextProxy(const FString& Name, FSimpleMulticastDelegate* InSharedDrawEvent, ImFontAtlas* InFontAtlas);
 	~FImGuiContextProxy();
 
 	FImGuiContextProxy(const FImGuiContextProxy&) = delete;

Source/ImGui/Private/ImGuiImplementation.cpp

@@ -32,29 +32,18 @@
 
 namespace ImGuiImplementation
 {
-	// This is exposing ImGui default context for the whole module.
-	// This is assuming that we don't define custom GImGui and therefore have GImDefaultContext defined in imgui.cpp.
-	ImGuiContext& GetDefaultContext()
+	bool GetCursorData(ImGuiMouseCursor CursorType, FVector2D& OutSize, FVector2D& OutUVMin, FVector2D& OutUVMax, FVector2D& OutOutlineUVMin, FVector2D& OutOutlineUVMax)
 	{
-		return GImDefaultContext;
-	}
-
-	void SaveCurrentContextIniSettings(const char* Filename)
-	{
-		SaveIniSettingsToDisk(Filename);
-	}
-
-	bool GetCursorData(int CursorType, FVector2D& OutSize, FVector2D& OutUVMin, FVector2D& OutUVMax, FVector2D& OutOutlineUVMin, FVector2D& OutOutlineUVMax)
-	{
-		if (static_cast<unsigned>(CursorType) < static_cast<unsigned>(ImGuiMouseCursor_Count_))
+		ImFontAtlas* FontAtlas = ImGui::GetIO().Fonts;
+		ImVec2 Offset, Size, UV[4];
+		if (FontAtlas && FontAtlas->GetMouseCursorTexData(CursorType, &Offset, &Size, &UV[0], &UV[2]))
 		{
 			using namespace ImGuiInterops;
-			ImGuiMouseCursorData& CursorData = GImGui->MouseCursorData[CursorType];
-			OutSize = ToVector2D(CursorData.Size);
-			OutUVMin = ToVector2D(CursorData.TexUvMin[0]);
-			OutUVMax = ToVector2D(CursorData.TexUvMax[0]);
-			OutOutlineUVMin = ToVector2D(CursorData.TexUvMin[1]);
-			OutOutlineUVMax = ToVector2D(CursorData.TexUvMax[1]);
+			OutSize = ToVector2D(Size);
+			OutUVMin = ToVector2D(UV[0]);
+			OutUVMax = ToVector2D(UV[1]);
+			OutOutlineUVMin = ToVector2D(UV[2]);
+			OutOutlineUVMax = ToVector2D(UV[3]);
 			return true;
 		}
 		else

Source/ImGui/Private/ImGuiImplementation.h

@@ -8,12 +8,6 @@
 // Gives access to selected ImGui implementation features.
 namespace ImGuiImplementation
 {
-	// Get default context created by ImGui framework.
-	ImGuiContext& GetDefaultContext();
-
-	// Save current context settings.
-	void SaveCurrentContextIniSettings(const char* Filename);
-
 	// Get specific cursor data.
-	bool GetCursorData(int CursorType, FVector2D& OutSize, FVector2D& OutUVMin, FVector2D& OutUVMax, FVector2D& OutOutlineUVMin, FVector2D& OutOutlineUVMax);
+	bool GetCursorData(ImGuiMouseCursor CursorType, FVector2D& OutSize, FVector2D& OutUVMin, FVector2D& OutUVMax, FVector2D& OutOutlineUVMin, FVector2D& OutOutlineUVMax);
 }

Source/ImGui/Private/ImGuiInteroperability.cpp

@@ -141,7 +141,7 @@ namespace ImGuiInterops
 			return EMouseCursor::Default;
 		case ImGuiMouseCursor_TextInput:
 			return EMouseCursor::TextEditBeam;
-		case ImGuiMouseCursor_Move:
+		case ImGuiMouseCursor_ResizeAll:
 			return EMouseCursor::CardinalCross;
 		case ImGuiMouseCursor_ResizeNS:
 			return  EMouseCursor::ResizeUpDown;

Source/ImGui/Private/ImGuiModuleManager.cpp

@@ -76,17 +76,16 @@ void FImGuiModuleManager::LoadTextures()
 	TextureManager.CreatePlainTexture(FName{ "ImGuiModule_Plain" }, 2, 2, FColor::White);
 
 	// Create a font atlas texture.
-	ImFontAtlas* Fonts = ImGui::GetIO().Fonts;
-	checkf(Fonts, TEXT("Invalid font atlas."));
+	ImFontAtlas& Fonts = ContextManager.GetFontAtlas();
 
 	unsigned char* Pixels;
 	int Width, Height, Bpp;
-	Fonts->GetTexDataAsRGBA32(&Pixels, &Width, &Height, &Bpp);
+	Fonts.GetTexDataAsRGBA32(&Pixels, &Width, &Height, &Bpp);
 
 	TextureIndex FontsTexureIndex = TextureManager.CreateTexture(FName{ "ImGuiModule_FontAtlas" }, Width, Height, Bpp, Pixels, false);
 
 	// Set font texture index in ImGui.
-	Fonts->TexID = ImGuiInterops::ToImTextureID(FontsTexureIndex);
+	Fonts.TexID = ImGuiInterops::ToImTextureID(FontsTexureIndex);
 }
 
 void FImGuiModuleManager::RegisterTick()

Source/ImGui/Private/SImGuiWidget.cpp

@@ -692,7 +692,7 @@ bool SImGuiWidget::InFrameGrabbingRange(const FVector2D& Position, float Scale,
 
 	// Get the grab range based on cursor shape.
 	FVector2D Size, UVMin, UVMax, OutlineUVMin, OutlineUVMax;
-	const float Range = ImGuiImplementation::GetCursorData(ImGuiMouseCursor_Move, Size, UVMin, UVMax, OutlineUVMin, OutlineUVMax)
+	const float Range = ImGuiImplementation::GetCursorData(ImGuiMouseCursor_ResizeAll, Size, UVMin, UVMax, OutlineUVMin, OutlineUVMax)
 		? Size.GetMax() * 0.5f + 5.f : 25.f;
 
 	return (Position - ViewportCenter).GetAbsMax() <= Range;
@@ -887,7 +887,7 @@ int32 SImGuiWidget::OnPaint(const FPaintArgs& Args, const FGeometry& AllottedGeo
 
 				// Draw a movement gizmo (using ImGui move cursor).
 				FVector2D Size, UVMin, UVMax, OutlineUVMin, OutlineUVMax;
-				if (ImGuiImplementation::GetCursorData(ImGuiMouseCursor_Move, Size, UVMin, UVMax, OutlineUVMin, OutlineUVMax))
+				if (ImGuiImplementation::GetCursorData(ImGuiMouseCursor_ResizeAll, Size, UVMin, UVMax, OutlineUVMin, OutlineUVMax))
 				{
 					const TextureIndex FontAtlasIndex = ModuleManager->GetTextureManager().FindTextureIndex(FName{ FontAtlasTextureName });
 					if (FontAtlasIndex != INDEX_NONE)