From c9d3c29aa33aee77c99b46a8135469cde544b2ca Mon Sep 17 00:00:00 2001
From: sneakyevil <sneakyevildogs@gmail.com>
Date: Tue, 5 Sep 2023 13:20:48 +0200
Subject: [PATCH] Backend: Win32: support keyboard codepage conversion for when
 compiling in MBCS mode and creating a non-Unicode window. (#6785, #6782,
 #5725)

---
 backends/imgui_impl_win32.cpp | 18 +++++++++++++++++-
 docs/CHANGELOG.txt            |  2 ++
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/backends/imgui_impl_win32.cpp b/backends/imgui_impl_win32.cpp
index 0993ecf8c..f3c339149 100644
--- a/backends/imgui_impl_win32.cpp
+++ b/backends/imgui_impl_win32.cpp
@@ -36,6 +36,7 @@ typedef DWORD (WINAPI *PFN_XInputGetState)(DWORD, XINPUT_STATE*);
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2023-09-07: Inputs: Added support for keyboard codepage conversion for when application is compiled in MBCS mode and using a non-Unicode window.
 //  2023-04-19: Added ImGui_ImplWin32_InitForOpenGL() to facilitate combining raw Win32/Winapi with OpenGL. (#3218)
 //  2023-04-04: Inputs: Added support for io.AddMouseSourceEvent() to discriminate ImGuiMouseSource_Mouse/ImGuiMouseSource_TouchScreen/ImGuiMouseSource_Pen. (#2702)
 //  2023-02-15: Inputs: Use WM_NCMOUSEMOVE / WM_NCMOUSELEAVE to track mouse position over non-client area (e.g. OS decorations) when app is not focused. (#6045, #6162)
@@ -94,6 +95,7 @@ struct ImGui_ImplWin32_Data
     INT64                       Time;
     INT64                       TicksPerSecond;
     ImGuiMouseCursor            LastMouseCursor;
+    UINT32                      KeyboardCodePage;
 
 #ifndef IMGUI_IMPL_WIN32_DISABLE_GAMEPAD
     bool                        HasGamepad;
@@ -116,6 +118,16 @@ static ImGui_ImplWin32_Data* ImGui_ImplWin32_GetBackendData()
 }
 
 // Functions
+static void ImGui_ImplWin32_UpdateKeyboardCodePage()
+{
+    // Retrieve keyboard code page, required for handling of non-Unicode Windows.
+    ImGui_ImplWin32_Data* bd = ImGui_ImplWin32_GetBackendData();
+    HKL keyboard_layout = ::GetKeyboardLayout(0);
+    LCID keyboard_lcid = MAKELCID(HIWORD(keyboard_layout), SORT_DEFAULT);
+    if (::GetLocaleInfoA(keyboard_lcid, (LOCALE_RETURN_NUMBER | LOCALE_IDEFAULTANSICODEPAGE), (LPSTR)&bd->KeyboardCodePage, sizeof(bd->KeyboardCodePage)) == 0)
+        bd->KeyboardCodePage = CP_ACP; // Fallback to default ANSI code page when fails.
+}
+
 static bool ImGui_ImplWin32_InitEx(void* hwnd, bool platform_has_own_dc)
 {
     ImGuiIO& io = ImGui::GetIO();
@@ -138,6 +150,7 @@ static bool ImGui_ImplWin32_InitEx(void* hwnd, bool platform_has_own_dc)
     bd->TicksPerSecond = perf_frequency;
     bd->Time = perf_counter;
     bd->LastMouseCursor = ImGuiMouseCursor_COUNT;
+    ImGui_ImplWin32_UpdateKeyboardCodePage();
 
     // Set platform dependent data in viewport
     ImGui::GetMainViewport()->PlatformHandleRaw = (void*)hwnd;
@@ -671,6 +684,9 @@ IMGUI_IMPL_API LRESULT ImGui_ImplWin32_WndProcHandler(HWND hwnd, UINT msg, WPARA
     case WM_KILLFOCUS:
         io.AddFocusEvent(msg == WM_SETFOCUS);
         return 0;
+    case WM_INPUTLANGCHANGE:
+        ImGui_ImplWin32_UpdateKeyboardCodePage();
+        return 0;
     case WM_CHAR:
         if (::IsWindowUnicode(hwnd))
         {
@@ -681,7 +697,7 @@ IMGUI_IMPL_API LRESULT ImGui_ImplWin32_WndProcHandler(HWND hwnd, UINT msg, WPARA
         else
         {
             wchar_t wch = 0;
-            ::MultiByteToWideChar(CP_ACP, MB_PRECOMPOSED, (char*)&wParam, 1, &wch, 1);
+            ::MultiByteToWideChar(bd->KeyboardCodePage, MB_PRECOMPOSED, (char*)&wParam, 1, &wch, 1);
             io.AddInputCharacter(wch);
         }
         return 0;
diff --git a/docs/CHANGELOG.txt b/docs/CHANGELOG.txt
index 183c1151d..2d85903cf 100644
--- a/docs/CHANGELOG.txt
+++ b/docs/CHANGELOG.txt
@@ -52,6 +52,8 @@ Other changes:
   Was most often noticable when using an horizontal scrollbar. (#6789)
 - ImDrawList: Added AddEllipse(), AddEllipseFilled(), PathEllipticalArcTo(). (#2743) [@Doohl]
 - Backends: GLFW: Clear emscripten's MouseWheel callback before shutdown. (#6790, #6096, #4019) [@halx99]
+- Backends: Win32: Added support for keyboard codepage conversion for when application
+  is compiled in MBCS mode and using a non-Unicode window. (#6785, #6782, #5725, #5961) [@sneakyevil]
 
 
 -----------------------------------------------------------------------