Support IME composition strings of arbitrary length

Previously, IME composition strings were limited to at most 32 bytes, e.g. 10 Hiragana characters. Now, `SDL_TextEditingExtEvent` (`SDL_TEXTEDITING_EXT`) is supported, which uses heap-allocated composition strings of arbitrary length.

On the other hand, the buffer for input event text was larger than necessary, as SDL text events only contain at most 32 bytes (`SDL_TEXTINPUTEVENT_TEXT_SIZE` is not used directly to avoid the include). With the hint for extended IME handling enabled, long composition text will be sent as multiple text events (without breaking UTF-8).

src/engine/client/client.cpp

@@ -4562,6 +4562,11 @@ int main(int argc, const char **argv)
 	SDL_SetHint("SDL_TOUCH_MOUSE_EVENTS", "0");
 	SDL_SetHint("SDL_MOUSE_TOUCH_EVENTS", "0");
 
+	// Support longer IME composition strings (enables SDL_TEXTEDITING_EXT).
+#if SDL_VERSION_ATLEAST(2, 0, 22)
+	SDL_SetHint(SDL_HINT_IME_SUPPORT_EXTENDED_TEXT, "1");
+#endif
+
 #if defined(CONF_PLATFORM_MACOS)
 	// Hints will not be set if there is an existing override hint or environment variable that takes precedence.
 	// So this respects cli environment overrides.

src/engine/client/input.cpp

@@ -70,7 +70,6 @@ CInput::CInput()
 
 	m_pClipboardText = nullptr;
 
-	m_CompositionLength = COMP_LENGTH_INACTIVE;
 	m_CompositionCursor = 0;
 	m_CandidateSelectedIndex = -1;
 
@@ -328,9 +327,8 @@ void CInput::StopTextInput()
 	SDL_StopTextInput();
 	// disable system messages for performance
 	SDL_EventState(SDL_SYSWMEVENT, SDL_DISABLE);
-	m_CompositionLength = COMP_LENGTH_INACTIVE;
+	m_CompositionString = "";
 	m_CompositionCursor = 0;
-	m_aComposition[0] = '\0';
 	m_vCandidates.clear();
 }
 
@@ -574,6 +572,26 @@ void CInput::HandleTouchMotionEvent(const SDL_TouchFingerEvent &Event)
 	}
 }
 
+void CInput::HandleTextEditingEvent(const char *pText, int Start, int Length)
+{
+	if(pText[0] != '\0')
+	{
+		m_CompositionString = pText;
+		m_CompositionCursor = 0;
+		for(int i = 0; i < Start; i++)
+		{
+			m_CompositionCursor = str_utf8_forward(m_CompositionString.c_str(), m_CompositionCursor);
+		}
+		// Length is currently unused on Windows and will always be 0, so we don't support selecting composition text
+		AddTextEvent("");
+	}
+	else
+	{
+		m_CompositionString = "";
+		m_CompositionCursor = 0;
+	}
+}
+
 void CInput::SetCompositionWindowPosition(float X, float Y, float H)
 {
 	SDL_Rect Rect;
@@ -658,29 +676,18 @@ int CInput::Update()
 			break;
 
 		case SDL_TEXTEDITING:
-		{
-			m_CompositionLength = str_length(Event.edit.text);
-			if(m_CompositionLength)
-			{
-				str_copy(m_aComposition, Event.edit.text);
-				m_CompositionCursor = 0;
-				for(int i = 0; i < Event.edit.start; i++)
-					m_CompositionCursor = str_utf8_forward(m_aComposition, m_CompositionCursor);
-				// Event.edit.length is currently unused on Windows and will always be 0, so we don't support selecting composition text
-				AddTextEvent("");
-			}
-			else
-			{
-				m_aComposition[0] = '\0';
-				m_CompositionLength = 0;
-				m_CompositionCursor = 0;
-			}
+			HandleTextEditingEvent(Event.edit.text, Event.edit.start, Event.edit.length);
 			break;
-		}
+
+#if SDL_VERSION_ATLEAST(2, 0, 22)
+		case SDL_TEXTEDITING_EXT:
+			HandleTextEditingEvent(Event.editExt.text, Event.editExt.start, Event.editExt.length);
+			SDL_free(Event.editExt.text);
+			break;
+#endif
 
 		case SDL_TEXTINPUT:
-			m_aComposition[0] = '\0';
-			m_CompositionLength = COMP_LENGTH_INACTIVE;
+			m_CompositionString = "";
 			m_CompositionCursor = 0;
 			AddTextEvent(Event.text.text);
 			break;
@@ -861,9 +868,6 @@ int CInput::Update()
 		}
 	}
 
-	if(m_CompositionLength == 0)
-		m_CompositionLength = COMP_LENGTH_INACTIVE;
-
 	return 0;
 }
 

src/engine/client/input.h

@@ -84,9 +84,8 @@ class CInput : public IEngineInput
 #endif
 
 	// IME support
-	char m_aComposition[MAX_COMPOSITION_ARRAY_SIZE];
+	std::string m_CompositionString;
 	int m_CompositionCursor;
-	int m_CompositionLength;
 	std::vector<std::string> m_vCandidates;
 	int m_CandidateSelectedIndex;
 
@@ -113,6 +112,7 @@ class CInput : public IEngineInput
 	void HandleTouchDownEvent(const SDL_TouchFingerEvent &Event);
 	void HandleTouchUpEvent(const SDL_TouchFingerEvent &Event);
 	void HandleTouchMotionEvent(const SDL_TouchFingerEvent &Event);
+	void HandleTextEditingEvent(const char *pText, int Start, int Length);
 
 	char m_aDropFile[IO_MAX_PATH_LENGTH];
 
@@ -155,10 +155,10 @@ class CInput : public IEngineInput
 
 	void StartTextInput() override;
 	void StopTextInput() override;
-	const char *GetComposition() const override { return m_aComposition; }
-	bool HasComposition() const override { return m_CompositionLength != COMP_LENGTH_INACTIVE; }
+	const char *GetComposition() const override { return m_CompositionString.c_str(); }
+	bool HasComposition() const override { return !m_CompositionString.empty(); }
 	int GetCompositionCursor() const override { return m_CompositionCursor; }
-	int GetCompositionLength() const override { return m_CompositionLength; }
+	int GetCompositionLength() const override { return m_CompositionString.length(); }
 	const char *GetCandidate(int Index) const override { return m_vCandidates[Index].c_str(); }
 	int GetCandidateCount() const override { return m_vCandidates.size(); }
 	int GetCandidateSelectedIndex() const override { return m_CandidateSelectedIndex; }

src/engine/input.h

@@ -19,18 +19,13 @@ class IInput : public IInterface
 {
 	MACRO_INTERFACE("input")
 public:
-	enum
-	{
-		INPUT_TEXT_SIZE = 32 * UTF8_BYTE_LENGTH + 1,
-	};
-
 	class CEvent
 	{
 	public:
 		int m_Flags;
 		int m_Key;
 		uint32_t m_InputCount;
-		char m_aText[INPUT_TEXT_SIZE];
+		char m_aText[32]; // SDL_TEXTINPUTEVENT_TEXT_SIZE
 	};
 
 	enum
@@ -45,12 +40,6 @@ class IInput : public IInterface
 		CURSOR_MOUSE,
 		CURSOR_JOYSTICK,
 	};
-	enum
-	{
-		MAX_COMPOSITION_ARRAY_SIZE = 32, // SDL2 limitation
-
-		COMP_LENGTH_INACTIVE = -1,
-	};
 
 	// events
 	virtual void ConsumeEvents(std::function<void(const CEvent &Event)> Consumer) const = 0;