Made internal clipboard/IME handlers not rely on implicit GImGui context (#5856)

Code in SetPlatformImeDataFn_DefaultImpl amends 3a90dc389 by temporarily setting field in caller site.

imgui.cpp

@@ -991,8 +991,8 @@ static void             WindowSettingsHandler_ApplyAll(ImGuiContext*, ImGuiSetti
 static void             WindowSettingsHandler_WriteAll(ImGuiContext*, ImGuiSettingsHandler*, ImGuiTextBuffer* buf);
 
 // Platform Dependents default implementation for IO functions
-static const char*      GetClipboardTextFn_DefaultImpl(void* user_data);
-static void             SetClipboardTextFn_DefaultImpl(void* user_data, const char* text);
+static const char*      GetClipboardTextFn_DefaultImpl(void* user_data_ctx);
+static void             SetClipboardTextFn_DefaultImpl(void* user_data_ctx, const char* text);
 static void             SetPlatformImeDataFn_DefaultImpl(ImGuiViewport* viewport, ImGuiPlatformImeData* data);
 
 namespace ImGui
@@ -1220,12 +1220,9 @@ ImGuiIO::ImGuiIO()
     ConfigMemoryCompactTimer = 60.0f;
 
     // Platform Functions
+    // Note: Initialize() will setup default clipboard/ime handlers.
     BackendPlatformName = BackendRendererName = NULL;
     BackendPlatformUserData = BackendRendererUserData = BackendLanguageUserData = NULL;
-    GetClipboardTextFn = GetClipboardTextFn_DefaultImpl;   // Platform dependent default implementations
-    SetClipboardTextFn = SetClipboardTextFn_DefaultImpl;
-    ClipboardUserData = NULL;
-    SetPlatformImeDataFn = SetPlatformImeDataFn_DefaultImpl;
 
     // Input (NB: we already have memset zero the entire structure!)
     MousePos = ImVec2(-FLT_MAX, -FLT_MAX);
@@ -3496,6 +3493,12 @@ void ImGui::Initialize()
     // Setup default localization table
     LocalizeRegisterEntries(GLocalizationEntriesEnUS, IM_ARRAYSIZE(GLocalizationEntriesEnUS));
 
+    // Setup default platform clipboard/IME handlers.
+    g.IO.GetClipboardTextFn = GetClipboardTextFn_DefaultImpl;    // Platform dependent default implementations
+    g.IO.SetClipboardTextFn = SetClipboardTextFn_DefaultImpl;
+    g.IO.ClipboardUserData = (void*)&g;                          // Default implementation use the ImGuiContext as user data (ideally those would be arguments to the function)
+    g.IO.SetPlatformImeDataFn = SetPlatformImeDataFn_DefaultImpl;
+
     // Create default viewport
     ImGuiViewportP* viewport = IM_NEW(ImGuiViewportP)();
     g.Viewports.push_back(viewport);
@@ -4837,7 +4840,19 @@ void ImGui::EndFrame()
     if (g.IO.SetPlatformImeDataFn && memcmp(ime_data, &g.PlatformImeDataPrev, sizeof(ImGuiPlatformImeData)) != 0)
     {
         IMGUI_DEBUG_LOG_IO("Calling io.SetPlatformImeDataFn(): WantVisible: %d, InputPos (%.2f,%.2f)\n", ime_data->WantVisible, ime_data->InputPos.x, ime_data->InputPos.y);
-        g.IO.SetPlatformImeDataFn(GetMainViewport(), ime_data);
+        ImGuiViewport* viewport = GetMainViewport();
+#ifndef IMGUI_DISABLE_OBSOLETE_FUNCTIONS
+        if (viewport->PlatformHandleRaw == NULL && g.IO.ImeWindowHandle != NULL)
+        {
+            viewport->PlatformHandleRaw = g.IO.ImeWindowHandle;
+            g.IO.SetPlatformImeDataFn(viewport, ime_data);
+            viewport->PlatformHandleRaw = NULL;
+        }
+        else
+#endif
+        {
+            g.IO.SetPlatformImeDataFn(viewport, ime_data);
+        }
     }
 
     // Hide implicit/fallback "Debug" window if it hasn't been used
@@ -12893,9 +12908,9 @@ static void ImGui::UpdateViewportsNewFrame()
 
 // Win32 clipboard implementation
 // We use g.ClipboardHandlerData for temporary storage to ensure it is freed on Shutdown()
-static const char* GetClipboardTextFn_DefaultImpl(void*)
+static const char* GetClipboardTextFn_DefaultImpl(void* user_data_ctx)
 {
-    ImGuiContext& g = *GImGui;
+    ImGuiContext& g = *(ImGuiContext*)user_data_ctx;
     g.ClipboardHandlerData.clear();
     if (!::OpenClipboard(NULL))
         return NULL;
@@ -12956,8 +12971,9 @@ static void SetClipboardTextFn_DefaultImpl(void*, const char* text)
     }
 }
 
-static const char* GetClipboardTextFn_DefaultImpl(void*)
+static const char* GetClipboardTextFn_DefaultImpl(void* user_data_ctx)
 {
+    ImGuiContext& g = *(ImGuiContext*)user_data_ctx;
     if (!main_clipboard)
         PasteboardCreate(kPasteboardClipboard, &main_clipboard);
     PasteboardSynchronize(main_clipboard);
@@ -12975,7 +12991,6 @@ static const char* GetClipboardTextFn_DefaultImpl(void*)
             CFDataRef cf_data;
             if (PasteboardCopyItemFlavorData(main_clipboard, item_id, CFSTR("public.utf8-plain-text"), &cf_data) == noErr)
             {
-                ImGuiContext& g = *GImGui;
                 g.ClipboardHandlerData.clear();
                 int length = (int)CFDataGetLength(cf_data);
                 g.ClipboardHandlerData.resize(length + 1);
@@ -12992,15 +13007,15 @@ static const char* GetClipboardTextFn_DefaultImpl(void*)
 #else
 
 // Local Dear ImGui-only clipboard implementation, if user hasn't defined better clipboard handlers.
-static const char* GetClipboardTextFn_DefaultImpl(void*)
+static const char* GetClipboardTextFn_DefaultImpl(void* user_data_ctx)
 {
-    ImGuiContext& g = *GImGui;
+    ImGuiContext& g = *(ImGuiContext*)user_data_ctx;
     return g.ClipboardHandlerData.empty() ? NULL : g.ClipboardHandlerData.begin();
 }
 
-static void SetClipboardTextFn_DefaultImpl(void*, const char* text)
+static void SetClipboardTextFn_DefaultImpl(void* user_data_ctx, const char* text)
 {
-    ImGuiContext& g = *GImGui;
+    ImGuiContext& g = *(ImGuiContext*)user_data_ctx;
     g.ClipboardHandlerData.clear();
     const char* text_end = text + strlen(text);
     g.ClipboardHandlerData.resize((int)(text_end - text) + 1);
@@ -13022,10 +13037,6 @@ static void SetPlatformImeDataFn_DefaultImpl(ImGuiViewport* viewport, ImGuiPlatf
 {
     // Notify OS Input Method Editor of text input position
     HWND hwnd = (HWND)viewport->PlatformHandleRaw;
-#ifndef IMGUI_DISABLE_OBSOLETE_FUNCTIONS
-    if (hwnd == 0)
-        hwnd = (HWND)ImGui::GetIO().ImeWindowHandle;
-#endif
     if (hwnd == 0)
         return;