From 869f0d0f65c17709c5794a63c91e2f467d0e839c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jan=20Lup=C4=8D=C3=ADk?= <shawnczek@truckersmp.com>
Date: Fri, 28 Jun 2024 22:52:32 +0200
Subject: [PATCH] Complete the composition when the user tries to interact with
 other elements.

---
 Backends/RmlUi_Platform_Win32.cpp | 54 +++++++++++++++++++------------
 Backends/RmlUi_Platform_Win32.h   |  2 +-
 2 files changed, 34 insertions(+), 22 deletions(-)

diff --git a/Backends/RmlUi_Platform_Win32.cpp b/Backends/RmlUi_Platform_Win32.cpp
index b12735cd6..506fe7009 100644
--- a/Backends/RmlUi_Platform_Win32.cpp
+++ b/Backends/RmlUi_Platform_Win32.cpp
@@ -214,6 +214,15 @@ static std::wstring IMEGetCompositionString(HIMC context, bool finalize)
 #endif
 }
 
+static void IMECompleteComposition(HWND window_handle)
+{
+	if (HIMC context = ImmGetContext(window_handle))
+	{
+		ImmNotifyIME(context, NI_COMPOSITIONSTR, CPS_COMPLETE, NULL);
+		ImmReleaseContext(window_handle, context);
+	}
+}
+
 bool RmlWin32::WindowProcedure(Rml::Context* context, TextInputMethodEditor_Win32& text_input_method_editor, HWND window_handle, UINT message,
 	WPARAM w_param, LPARAM l_param)
 {
@@ -222,6 +231,12 @@ bool RmlWin32::WindowProcedure(Rml::Context* context, TextInputMethodEditor_Win3
 
 	static bool tracking_mouse_leave = false;
 
+	// If the user tries to interact with the window by using the mouse in any way, end the
+	// composition by committing the current string. This behavior is identical to other
+	// browsers and is expected, yet, Windows does not send any IME messages in such a case.
+	if (text_input_method_editor.IsComposing() && message >= WM_LBUTTONDOWN && message <= WM_MBUTTONDBLCLK)
+		IMECompleteComposition(window_handle);
+
 	bool result = true;
 
 	switch (message)
@@ -306,24 +321,24 @@ bool RmlWin32::WindowProcedure(Rml::Context* context, TextInputMethodEditor_Win3
 			text_input_method_editor.ConfirmComposition(Rml::StringView());
 		break;
 	case WM_IME_COMPOSITION:
+	{
+		HIMC imm_context = ImmGetContext(window_handle);
+
 		// Not every IME starts a composition.
 		if (!text_input_method_editor.IsComposing())
 			text_input_method_editor.StartComposition();
 
 		if (!!(l_param & GCS_CURSORPOS))
 		{
-			if (auto imm_context = ImmGetContext(window_handle))
-			{
-				// The cursor position is the wchar_t offset in the composition string. Because we
-				// work with UTF-8 and not UTF-16, we will have to convert the character offset.
-				int cursor_pos = IMEGetCursorPosition(imm_context);
+			// The cursor position is the wchar_t offset in the composition string. Because we
+			// work with UTF-8 and not UTF-16, we will have to convert the character offset.
+			int cursor_pos = IMEGetCursorPosition(imm_context);
 
-				std::wstring composition = IMEGetCompositionString(imm_context, false);
-				Rml::String converted = RmlWin32::ConvertToUTF8(composition.substr(0, cursor_pos));
-				cursor_pos = (int)Rml::StringUtilities::LengthUTF8(converted);
+			std::wstring composition = IMEGetCompositionString(imm_context, false);
+			Rml::String converted = RmlWin32::ConvertToUTF8(composition.substr(0, cursor_pos));
+			cursor_pos = (int)Rml::StringUtilities::LengthUTF8(converted);
 
-				text_input_method_editor.SetCursorPosition(cursor_pos, true);
-			}
+			text_input_method_editor.SetCursorPosition(cursor_pos, true);
 		}
 
 		if (!!(l_param & CS_NOMOVECARET))
@@ -335,26 +350,23 @@ bool RmlWin32::WindowProcedure(Rml::Context* context, TextInputMethodEditor_Win3
 
 		if (!!(l_param & GCS_RESULTSTR))
 		{
-			if (auto imm_context = ImmGetContext(window_handle))
-			{
-				std::wstring composition = IMEGetCompositionString(imm_context, true);
-				text_input_method_editor.ConfirmComposition(RmlWin32::ConvertToUTF8(composition));
-			}
+			std::wstring composition = IMEGetCompositionString(imm_context, true);
+			text_input_method_editor.ConfirmComposition(RmlWin32::ConvertToUTF8(composition));
 		}
 
 		if (!!(l_param & GCS_COMPSTR))
 		{
-			if (auto imm_context = ImmGetContext(window_handle))
-			{
-				std::wstring composition = IMEGetCompositionString(imm_context, false);
-				text_input_method_editor.SetComposition(RmlWin32::ConvertToUTF8(composition));
-			}
+			std::wstring composition = IMEGetCompositionString(imm_context, false);
+			text_input_method_editor.SetComposition(RmlWin32::ConvertToUTF8(composition));
 		}
 
 		// The composition has been canceled.
 		if (!l_param)
 			text_input_method_editor.CancelComposition();
-		break;
+
+		ImmReleaseContext(window_handle, imm_context);
+	}
+	break;
 	case WM_IME_CHAR:
 	case WM_IME_REQUEST:
 		// Ignore WM_IME_CHAR and WM_IME_REQUEST to block the system from appending the composition string.
diff --git a/Backends/RmlUi_Platform_Win32.h b/Backends/RmlUi_Platform_Win32.h
index 9a3994e53..32469e637 100644
--- a/Backends/RmlUi_Platform_Win32.h
+++ b/Backends/RmlUi_Platform_Win32.h
@@ -99,7 +99,7 @@ int GetKeyModifierState();
     Custom backend implementation of TextInputHandler to handle the system's Input Method Editor (IME).
     This version supports only one active text input context.
  */
-class TextInputMethodEditor_Win32 final : public Rml::TextInputHandler {
+class TextInputMethodEditor_Win32 final : public Rml::TextInputHandler, Rml::NonCopyMoveable {
 public:
 	TextInputMethodEditor_Win32();