Add support for IMEs on Linux

[y5nw]

This PR uses XSetLocaleModifiers to add support for IMEs.

To-Do

This pull request is ready for review.

• IME support only appears to work with certain locales (e.g. zh_CN) (this was tested with an older version of MT)
• TODO: Properly implement buffers for entering multiple characters at a time
• Fix: the position of the IME hint appears to be constantly at the bottom of the screen
• Fix: the IME is used in places where this behavior is not desired

Breaking changes

• There is now a EET_STRING_INPUT_EVENT event:
  • The corresponding event field is event.StringInput
  • event.StringInput.Str contains a reference to the core::stringw that contains the entered string
• IGUIElement now has a bool acceptsIME() method that returns whether the element accepts input from the IME:
  • true: keyboard input events are filtered by the IME before being passed to the element
  • false (default): keyboard input events are not filtered by the IME

References

• https://gist.github.com/baines/5a49f1334281b2685af5dcae81a6fa8a (accessed on 2021-03-30)
• https://www.x.org/releases/current/doc/libX11/libX11/libX11.pdf (last access on 2021-04-02)

[y5nw]

I also made the corresponding changes to Minetest. Should I post them now or should I wait for this PR to be merged?

[sfan5]

Posting them early is useful so they can be looked at or tested.

[y5nw]

diff --git a/src/gui/guiChatConsole.cpp b/src/gui/guiChatConsole.cpp
index a4e91fe78..dc688395b 100644
--- a/src/gui/guiChatConsole.cpp
+++ b/src/gui/guiChatConsole.cpp
@@ -619,6 +619,11 @@ bool GUIChatConsole::OnEvent(const SEvent& event)
 			m_chat_backend->scroll(rows);
 		}
 	}
+	else if(event.EventType == EET_STRING_INPUT_EVENT)
+	{
+		prompt.input(std::wstring(event.StringInput.Str->c_str()));
+		return true;
+	}
 
 	return Parent ? Parent->OnEvent(event) : false;
 }
diff --git a/src/gui/guiChatConsole.h b/src/gui/guiChatConsole.h
index 896342ab0..1152f2b2d 100644
--- a/src/gui/guiChatConsole.h
+++ b/src/gui/guiChatConsole.h
@@ -72,6 +72,8 @@ class GUIChatConsole : public gui::IGUIElement
 
 	virtual void setVisible(bool visible);
 
+	virtual bool acceptsIME() { return true; }
+
 private:
 	void reformatConsole();
 	void recalculateConsolePosition();
diff --git a/src/gui/guiEditBox.cpp b/src/gui/guiEditBox.cpp
index cd5a0868d..86cd2001e 100644
--- a/src/gui/guiEditBox.cpp
+++ b/src/gui/guiEditBox.cpp
@@ -216,6 +216,10 @@ bool GUIEditBox::OnEvent(const SEvent &event)
 			if (processMouse(event))
 				return true;
 			break;
+		case EET_STRING_INPUT_EVENT:
+			inputString(event.StringInput.Str);
+			return true;
+			break;
 		default:
 			break;
 		}
@@ -708,6 +712,46 @@ void GUIEditBox::inputChar(wchar_t c)
 	calculateScrollPos();
 }
 
+void GUIEditBox::inputString(core::stringw *str)
+{
+	if (!isEnabled() || !m_writable)
+		return;
+
+	if (str) {
+		u32 len = str->size();
+		if (Text.size()+len <= m_max || m_max == 0) {
+			core::stringw s;
+			if (m_mark_begin != m_mark_end) {
+				// clang-format off
+				// replace marked test
+				s32 real_begin = m_mark_begin < m_mark_end ? m_mark_begin : m_mark_end;
+				s32 real_end = m_mark_begin < m_mark_end ? m_mark_end : m_mark_begin;
+
+				s = Text.subString(0, real_begin);
+				s.append(*str);
+				s.append(Text.subString(real_end, Text.size() - real_end));
+				Text = s;
+				m_cursor_pos = real_begin + len;
+				// clang-format on
+			} else {
+				// append string
+				s = Text.subString(0, m_cursor_pos);
+				s.append(*str);
+				s.append(Text.subString(m_cursor_pos,
+						Text.size() - m_cursor_pos));
+				Text = s;
+				m_cursor_pos += len;
+			}
+
+			m_blink_start_time = porting::getTimeMs();
+			setTextMarkers(0, 0);
+		}
+	}
+	breakText();
+	sendGuiEvent(EGET_EDITBOX_CHANGED);
+	calculateScrollPos();
+}
+
 bool GUIEditBox::processMouse(const SEvent &event)
 {
 	switch (event.MouseInput.Event) {
diff --git a/src/gui/guiEditBox.h b/src/gui/guiEditBox.h
index c616d75d1..da5628b6b 100644
--- a/src/gui/guiEditBox.h
+++ b/src/gui/guiEditBox.h
@@ -138,6 +138,8 @@ class GUIEditBox : public IGUIEditBox
 	virtual void deserializeAttributes(
 			io::IAttributes *in, io::SAttributeReadWriteOptions *options);
 
+	virtual bool acceptsIME() { return isEnabled() && m_writable; };
+
 protected:
 	virtual void breakText() = 0;
 
@@ -156,6 +158,7 @@ class GUIEditBox : public IGUIEditBox
 	virtual s32 getCursorPos(s32 x, s32 y) = 0;
 
 	bool processKey(const SEvent &event);
+	virtual void inputString(core::stringw *str);
 	virtual void inputChar(wchar_t c);
 
 	//! returns the line number that the cursor is on

[sfan5]

Works great aside from the code comments, good job 👍.

[y5nw]

Here is the fixup patch to keep GUIEditBox::inputString consistent with CGUIEditBox in Irrlicht:

diff --git a/src/gui/guiEditBox.cpp b/src/gui/guiEditBox.cpp
index 86cd2001e..260589f02 100644
--- a/src/gui/guiEditBox.cpp
+++ b/src/gui/guiEditBox.cpp
@@ -217,7 +217,7 @@ bool GUIEditBox::OnEvent(const SEvent &event)
 				return true;
 			break;
 		case EET_STRING_INPUT_EVENT:
-			inputString(event.StringInput.Str);
+			inputString(*event.StringInput.Str);
 			return true;
 			break;
 		default:
@@ -674,79 +674,44 @@ bool GUIEditBox::onKeyDelete(const SEvent &event, s32 &mark_begin, s32 &mark_end
 
 void GUIEditBox::inputChar(wchar_t c)
 {
-	if (!isEnabled() || !m_writable)
-		return;
-
-	if (c != 0) {
-		if (Text.size() < m_max || m_max == 0) {
-			core::stringw s;
-
-			if (m_mark_begin != m_mark_end) {
-				// clang-format off
-				// replace marked text
-				s32 real_begin = m_mark_begin < m_mark_end ? m_mark_begin : m_mark_end;
-				s32 real_end = m_mark_begin < m_mark_end ? m_mark_end : m_mark_begin;
-
-				s = Text.subString(0, real_begin);
-				s.append(c);
-				s.append(Text.subString(real_end, Text.size() - real_end));
-				Text = s;
-				m_cursor_pos = real_begin + 1;
-				// clang-format on
-			} else {
-				// add new character
-				s = Text.subString(0, m_cursor_pos);
-				s.append(c);
-				s.append(Text.subString(m_cursor_pos,
-						Text.size() - m_cursor_pos));
-				Text = s;
-				++m_cursor_pos;
-			}
-
-			m_blink_start_time = porting::getTimeMs();
-			setTextMarkers(0, 0);
-		}
-	}
-	breakText();
-	sendGuiEvent(EGET_EDITBOX_CHANGED);
-	calculateScrollPos();
+	core::stringw s(&c, 1);
+	inputString(s);
 }
 
-void GUIEditBox::inputString(core::stringw *str)
+void GUIEditBox::inputString(const core::stringw &str)
 {
 	if (!isEnabled() || !m_writable)
 		return;
 
-	if (str) {
-		u32 len = str->size();
-		if (Text.size()+len <= m_max || m_max == 0) {
-			core::stringw s;
-			if (m_mark_begin != m_mark_end) {
-				// clang-format off
-				// replace marked test
-				s32 real_begin = m_mark_begin < m_mark_end ? m_mark_begin : m_mark_end;
-				s32 real_end = m_mark_begin < m_mark_end ? m_mark_end : m_mark_begin;
-
-				s = Text.subString(0, real_begin);
-				s.append(*str);
-				s.append(Text.subString(real_end, Text.size() - real_end));
-				Text = s;
-				m_cursor_pos = real_begin + len;
-				// clang-format on
-			} else {
-				// append string
-				s = Text.subString(0, m_cursor_pos);
-				s.append(*str);
-				s.append(Text.subString(m_cursor_pos,
-						Text.size() - m_cursor_pos));
-				Text = s;
-				m_cursor_pos += len;
-			}
-
-			m_blink_start_time = porting::getTimeMs();
-			setTextMarkers(0, 0);
+	u32 len = str.size();
+	if (Text.size()+len <= m_max || m_max == 0) {
+		core::stringw s;
+		if (m_mark_begin != m_mark_end) {
+			// clang-format off
+			// replace marked test
+			s32 real_begin = m_mark_begin < m_mark_end ? m_mark_begin : m_mark_end;
+			s32 real_end = m_mark_begin < m_mark_end ? m_mark_end : m_mark_begin;
+
+			s = Text.subString(0, real_begin);
+			s.append(str);
+			s.append(Text.subString(real_end, Text.size() - real_end));
+			Text = s;
+			m_cursor_pos = real_begin + len;
+			// clang-format on
+		} else {
+			// append string
+			s = Text.subString(0, m_cursor_pos);
+			s.append(str);
+			s.append(Text.subString(m_cursor_pos,
+					Text.size() - m_cursor_pos));
+			Text = s;
+			m_cursor_pos += len;
 		}
+
+		m_blink_start_time = porting::getTimeMs();
+		setTextMarkers(0, 0);
 	}
+
 	breakText();
 	sendGuiEvent(EGET_EDITBOX_CHANGED);
 	calculateScrollPos();
diff --git a/src/gui/guiEditBox.h b/src/gui/guiEditBox.h
index da5628b6b..2a5c911bc 100644
--- a/src/gui/guiEditBox.h
+++ b/src/gui/guiEditBox.h
@@ -158,7 +158,7 @@ class GUIEditBox : public IGUIEditBox
 	virtual s32 getCursorPos(s32 x, s32 y) = 0;
 
 	bool processKey(const SEvent &event);
-	virtual void inputString(core::stringw *str);
+	virtual void inputString(const core::stringw &str);
 	virtual void inputChar(wchar_t c);
 
 	//! returns the line number that the cursor is on

[sfan5]

Thanks, I've squashed your commits and merged them.
You'll want to open a PR with the other changes on Minetest's repo.