Reload font manager in main thread to avoid a crash (#15900)

src/client/fontengine.cpp

@@ -18,10 +18,9 @@
 /** reference to access font engine, has to be initialized by main */
 FontEngine *g_fontengine = nullptr;
 
-/** callback to be used on change of font size setting */
+void FontEngine::fontSettingChanged(const std::string &name, void *userdata)
-static void font_setting_changed(const std::string &name, void *userdata)
 {
-	static_cast<FontEngine *>(userdata)->readSettings();
+	((FontEngine *)userdata)->m_needs_reload = true;
 }
 
 static const char *settings[] = {
@@ -49,7 +48,7 @@ FontEngine::FontEngine(gui::IGUIEnvironment* env) :
 	readSettings();
 
 	for (auto name : settings)
-		g_settings->registerChangedCallback(name, font_setting_changed, this);
+		g_settings->registerChangedCallback(name, fontSettingChanged, this);
 }
 
 FontEngine::~FontEngine()
@@ -162,6 +161,15 @@ void FontEngine::readSettings()
 	refresh();
 }
 
+void FontEngine::handleReload()
+{
+	if (!m_needs_reload)
+		return;
+
+	m_needs_reload = false;
+	readSettings();
+}
+
 void FontEngine::updateSkin()
 {
 	gui::IGUIFont *font = getFont();

src/client/fontengine.h

@@ -121,6 +121,9 @@ public:
 	/** update internal parameters from settings */
 	void readSettings();
 
+	/** reload fonts if settings were changed */
+	void handleReload();
+
 	void setMediaFont(const std::string &name, const std::string &data);
 
 	void clearMediaFonts();
@@ -142,6 +145,9 @@ private:
 	/** refresh after fonts have been changed */
 	void refresh();
 
+	/** callback to be used on change of font size setting */
+	static void fontSettingChanged(const std::string &name, void *userdata);
+
 	/** pointer to irrlicht gui environment */
 	gui::IGUIEnvironment* m_env = nullptr;
 
@@ -164,6 +170,8 @@ private:
 	/** default font engine mode (fixed) */
 	static const FontMode m_currentMode = FM_Standard;
 
+	bool m_needs_reload = false;
+
 	DISABLE_CLASS_COPY(FontEngine);
 };
 

src/client/game.cpp

@@ -970,6 +970,8 @@ void Game::run()
 
 		framemarker.start();
 
+		g_fontengine->handleReload();
+
 		const auto current_dynamic_info = ClientDynamicInfo::getCurrent();
 		if (!current_dynamic_info.equal(client_display_info)) {
 			client_display_info = current_dynamic_info;

src/gui/guiEngine.cpp

@@ -337,6 +337,8 @@ void GUIEngine::run()
 		fps_control.limit(device, &dtime);
 		framemarker.start();
 
+		g_fontengine->handleReload();
+
 		if (device->isWindowVisible()) {
 			// check if we need to update the "upper left corner"-text
 			if (text_height != g_fontengine->getTextHeight()) {