Fix Linux keyboard event handling (issue #2226)

Fixes a bug where key release events reported incorrect key codes when
multiple keys were pressed simultaneously. The original implementation
used a shared static KeyEvent variable that was overwritten by each key
press, causing releases to report the code of the last pressed key rather
than the key being released.

Removes the onCharInput callback and shared static variable, instead
calculating the KeyEvent directly from GLFW's parameters on both press
and release. This ensures each key event uses the correct code for that
specific key.

Note: This is a pragmatic fix for the immediate bug, but the underlying
architecture remains flawed. KeyEvent conflates two distinct concepts:
physical key events (for shortcuts, game input) and character input (for
text entry, Unicode). Issue #2337 highlights this confusion - users expect
KeyEvent codes to match shifted characters like '?', but codes should
represent physical keys.

The proper solution requires adding a separate keyChar() event type,
similar to Windows' WM_KEYDOWN/WM_KEYUP vs WM_CHAR separation. This
architectural change would affect all platforms and is beyond the scope
of this fix.

Fixes #2226
Related to #2337

Author: andrewfb

src/cinder/app/linux/AppImplLinuxGlfw.cpp

@@ -36,7 +36,6 @@ class GlfwCallbacks {
 public:
 
 	static std::map<GLFWwindow*, std::pair<AppImplLinux*,WindowRef>> sWindowMapping;
-	static KeyEvent sKeyEvent;
 	static bool sCapsLockDown, sNumLockDown, sScrollLockDown;
 
 	static void registerWindowEvents( GLFWwindow *glfwWindow, AppImplLinux* cinderAppImpl, const WindowRef& cinderWindow ) {
@@ -45,7 +44,7 @@ class GlfwCallbacks {
 		::glfwSetWindowSizeCallback( glfwWindow, GlfwCallbacks::onWindowSize );
 		::glfwSetWindowPosCallback( glfwWindow, GlfwCallbacks::onWindowMove );
 		::glfwSetKeyCallback( glfwWindow, GlfwCallbacks::onKeyboard );
-		::glfwSetCharCallback( glfwWindow, GlfwCallbacks::onCharInput );
+		// Note: NOT using glfwSetCharCallback - we compute characters directly in onKeyboard
 		::glfwSetCursorPosCallback( glfwWindow, GlfwCallbacks::onMousePos );
 		::glfwSetMouseButtonCallback( glfwWindow, GlfwCallbacks::onMouseButton );
 		::glfwSetScrollCallback( glfwWindow, GlfwCallbacks::onMouseWheel );
@@ -201,7 +200,7 @@ class GlfwCallbacks {
 			cinderAppImpl->setWindow( cinderWindow );
 
 			int32_t nativeKeyCode = KeyEvent::translateNativeKeyCode( key );
-			
+
 			if( glfwGetKey( glfwWindow, GLFW_KEY_CAPS_LOCK ) )
 				sCapsLockDown = ! sCapsLockDown;
 			if( glfwGetKey( glfwWindow, GLFW_KEY_NUM_LOCK ) )
@@ -210,38 +209,22 @@ class GlfwCallbacks {
 				sScrollLockDown = !sScrollLockDown;
 
 			auto modifiers = extractKeyModifiers( mods );
-			auto convertedChar = modifyChar( key, modifiers, sCapsLockDown );
-
-			if( GLFW_PRESS == action ) {
-				sKeyEvent = KeyEvent( cinderWindow, nativeKeyCode, 0, 0, modifiers, scancode );
-				// if convertedChar != 0, we'll get the unicode char value and wait until onCharInput is called.
-				// if convertedChar == 0, that means it is a non-unicode key (ex ctrl), so we'll emit the keydown here.
-				if( convertedChar == 0 ) {
-					cinderWindow->emitKeyDown( &sKeyEvent );
-				}
+			char convertedChar = modifyChar( key, modifiers, sCapsLockDown );
+			uint32_t charUtf32 = convertedChar ? (uint32_t)(unsigned char)convertedChar : 0;
+
+			// Calculate KeyEvent from GLFW's parameters on both press and release
+			KeyEvent keyEvent( cinderWindow, nativeKeyCode, charUtf32, convertedChar, modifiers, scancode );
+
+			if( GLFW_PRESS == action || GLFW_REPEAT == action ) {
+				cinderWindow->emitKeyDown( &keyEvent );
 			}
 			else if( GLFW_RELEASE == action ) {
-				KeyEvent event( cinderWindow, sKeyEvent.getCode(), sKeyEvent.getCharUtf32(), sKeyEvent.getChar(), modifiers, scancode );
-				sKeyEvent = {};
-				cinderWindow->emitKeyUp( &event );
+				cinderWindow->emitKeyUp( &keyEvent );
 			}
 		}
 	}
 
-	static void onCharInput( GLFWwindow *glfwWindow, unsigned int codepoint )
-	{
-		auto iter = sWindowMapping.find( glfwWindow );
-		if( sWindowMapping.end() != iter ) {
-			auto& cinderAppImpl = iter->second.first;
-			auto& cinderWindow = iter->second.second;
-			cinderAppImpl->setWindow( cinderWindow );
-
-			// create new sKeyEvent that includes same info as previous but also the utf32 char. emit key down signal with that
-			char asciiChar = codepoint < 256 ? (char)codepoint : 0;
-			sKeyEvent = KeyEvent( cinderWindow, sKeyEvent.getCode(), codepoint, asciiChar, sKeyEvent.getModifiers(), sKeyEvent.getNativeKeyCode() );
-			cinderWindow->emitKeyDown( &sKeyEvent );
-		}
-	}
+	// onCharInput removed - we now compute characters directly in onKeyboard
 
 	static void onMousePos( GLFWwindow* glfwWindow, double mouseX, double mouseY ) {
 		auto iter = sWindowMapping.find( glfwWindow );
@@ -327,7 +310,6 @@ class GlfwCallbacks {
 };
 
 std::map<GLFWwindow*, std::pair<AppImplLinux*,WindowRef>> GlfwCallbacks::sWindowMapping;
-KeyEvent GlfwCallbacks::sKeyEvent;
 bool GlfwCallbacks::sCapsLockDown = false;
 bool GlfwCallbacks::sNumLockDown = false;
 bool GlfwCallbacks::sScrollLockDown = false;