SDL2: Support highdpi (#14703)

and handle DPI changes at runtime

src/client/clientlauncher.cpp

@@ -69,6 +69,7 @@ static void dump_start_data(const GameStartData &data)
 ClientLauncher::~ClientLauncher()
 {
 	delete input;
+	g_settings->deregisterChangedCallback("dpi_change_notifier", setting_changed_callback, this);
 	g_settings->deregisterChangedCallback("gui_scaling", setting_changed_callback, this);
 
 	delete g_fontengine;
@@ -129,6 +130,7 @@ bool ClientLauncher::run(GameStartData &start_data, const Settings &cmd_args)
 
 	guienv = m_rendering_engine->get_gui_env();
 	config_guienv();
+	g_settings->registerChangedCallback("dpi_change_notifier", setting_changed_callback, this);
 	g_settings->registerChangedCallback("gui_scaling", setting_changed_callback, this);
 
 	g_fontengine = new FontEngine(guienv);

src/client/fontengine.cpp

@@ -59,7 +59,7 @@ FontEngine::FontEngine(gui::IGUIEnvironment* env) :
 		"mono_font_path", "mono_font_path_bold", "mono_font_path_italic",
 		"mono_font_path_bold_italic",
 		"fallback_font_path",
-		"screen_dpi", "gui_scaling",
+		"dpi_change_notifier", "gui_scaling",
 	};
 
 	for (auto name : settings)

src/client/hud.cpp

@@ -60,6 +60,7 @@ Hud::Hud(Client *client, LocalPlayer *player,
 	this->inventory   = inventory;
 
 	readScalingSetting();
+	g_settings->registerChangedCallback("dpi_change_notifier", setting_changed_callback, this);
 	g_settings->registerChangedCallback("hud_scaling", setting_changed_callback, this);
 
 	for (auto &hbar_color : hbar_colors)
@@ -153,6 +154,7 @@ void Hud::readScalingSetting()
 
 Hud::~Hud()
 {
+	g_settings->deregisterChangedCallback("dpi_change_notifier", setting_changed_callback, this);
 	g_settings->deregisterChangedCallback("hud_scaling", setting_changed_callback, this);
 
 	if (m_selection_mesh)

src/client/inputhandler.cpp

@@ -113,6 +113,15 @@ bool MyEventReceiver::OnEvent(const SEvent &event)
 		return true;
 	}
 
+	if (event.EventType == EET_APPLICATION_EVENT &&
+			event.ApplicationEvent.EventType == EAET_DPI_CHANGED) {
+		// This is a fake setting so that we can use (de)registerChangedCallback
+		// not only to listen for gui/hud_scaling changes, but also for DPI changes.
+		g_settings->setU16("dpi_change_notifier",
+				g_settings->getU16("dpi_change_notifier") + 1);
+		return true;
+	}
+
 	// This is separate from other keyboard handling so that it also works in menus.
 	if (event.EventType == EET_KEY_INPUT_EVENT) {
 		const KeyPress keyCode(event.KeyInput);

src/client/renderingengine.cpp

@@ -462,18 +462,14 @@ const VideoDriverInfo &RenderingEngine::getVideoDriverInfo(irr::video::E_DRIVER_
 
 float RenderingEngine::getDisplayDensity()
 {
+	float user_factor = g_settings->getFloat("display_density_factor", 0.5f, 5.0f);
 #ifndef __ANDROID__
-	static float cached_display_density = [&] {
-		float dpi = get_raw_device()->getDisplayDensity();
-		// fall back to manually specified dpi
-		if (dpi == 0.0f)
-			dpi = g_settings->getFloat("screen_dpi");
-		return dpi / 96.0f;
-	}();
-	return std::max(cached_display_density * g_settings->getFloat("display_density_factor"), 0.5f);
-
+	float dpi = get_raw_device()->getDisplayDensity();
+	if (dpi == 0.0f)
+		dpi = 96.0f;
+	return std::max(dpi / 96.0f * user_factor, 0.5f);
 #else // __ANDROID__
-	return porting::getDisplayDensity();
+	return porting::getDisplayDensity() * user_factor;
 #endif // __ANDROID__
 }
 

src/defaultsettings.cpp

@@ -536,8 +536,8 @@ void set_default_settings()
 	settings->setDefault("server_description", "");
 
 	settings->setDefault("enable_console", "false");
-	settings->setDefault("screen_dpi", "72");
 	settings->setDefault("display_density_factor", "1");
+	settings->setDefault("dpi_change_notifier", "0");
 
 	// Altered settings for macOS
 #if defined(__MACH__) && defined(__APPLE__)