Add input buffering framework

Input buffering is implicitly used by event accumulation, but this commit makes it more generic so it can be enabled for other uses.

For desktop OSs it's currently not feasible given main and UI threads are the same).

core/input/input.cpp

@@ -837,32 +837,40 @@ void Input::parse_input_event(const Ref<InputEvent> &p_event) {
 
 	ERR_FAIL_COND(p_event.is_null());
 
-	if (!use_accumulated_input) {
+	if (use_accumulated_input) {
+		if (buffered_events.is_empty() || !buffered_events.back()->get()->accumulate(p_event)) {
+			buffered_events.push_back(p_event);
+		}
+	} else if (use_input_buffering) {
+		buffered_events.push_back(p_event);
+	} else {
 		_parse_input_event_impl(p_event, false);
-		return;
 	}
-	if (!accumulated_events.is_empty() && accumulated_events.back()->get()->accumulate(p_event)) {
-		return; //event was accumulated, exit
-	}
-
-	accumulated_events.push_back(p_event);
 }
 
-void Input::flush_accumulated_events() {
+void Input::flush_buffered_events() {
 	_THREAD_SAFE_METHOD_
 
-	while (accumulated_events.front()) {
-		_parse_input_event_impl(accumulated_events.front()->get(), false);
-		accumulated_events.pop_front();
+	while (buffered_events.front()) {
+		_parse_input_event_impl(buffered_events.front()->get(), false);
+		buffered_events.pop_front();
 	}
 }
 
+bool Input::is_using_input_buffering() {
+	return use_input_buffering;
+}
+
+void Input::set_use_input_buffering(bool p_enable) {
+	use_input_buffering = p_enable;
+}
+
 void Input::set_use_accumulated_input(bool p_enable) {
 	use_accumulated_input = p_enable;
 }
 
 void Input::release_pressed_events() {
-	flush_accumulated_events(); // this is needed to release actions strengths
+	flush_buffered_events(); // this is needed to release actions strengths
 
 	keys_pressed.clear();
 	joy_buttons_pressed.clear();

core/input/input.h

@@ -111,6 +111,7 @@ private:
 
 	bool emulate_touch_from_mouse = false;
 	bool emulate_mouse_from_touch = false;
+	bool use_input_buffering = false;
 	bool use_accumulated_input = false;
 
 	int mouse_from_touch_index = -1;
@@ -213,7 +214,7 @@ private:
 
 	void _parse_input_event_impl(const Ref<InputEvent> &p_event, bool p_is_emulated);
 
-	List<Ref<InputEvent>> accumulated_events;
+	List<Ref<InputEvent>> buffered_events;
 
 	friend class DisplayServer;
 
@@ -323,7 +324,9 @@ public:
 	String get_joy_guid(int p_device) const;
 	void set_fallback_mapping(String p_guid);
 
-	void flush_accumulated_events();
+	void flush_buffered_events();
+	bool is_using_input_buffering();
+	void set_use_input_buffering(bool p_enable);
 	void set_use_accumulated_input(bool p_enable);
 
 	void release_pressed_events();

main/main.cpp

@@ -2587,6 +2587,11 @@ bool Main::iteration() {
 
 	iterating--;
 
+	// Needed for OSs using input buffering regardless accumulation (like Android)
+	if (Input::get_singleton()->is_using_input_buffering()) {
+		Input::get_singleton()->flush_buffered_events();
+	}
+
 	if (fixed_fps != -1) {
 		return exit;
 	}

platform/android/display_server_android.cpp

@@ -335,7 +335,7 @@ bool DisplayServerAndroid::can_any_window_draw() const {
 }
 
 void DisplayServerAndroid::process_events() {
-	Input::get_singleton()->flush_accumulated_events();
+	Input::get_singleton()->flush_buffered_events();
 }
 
 Vector<String> DisplayServerAndroid::get_rendering_drivers_func() {

platform/linuxbsd/display_server_x11.cpp

@@ -3433,7 +3433,7 @@ void DisplayServerX11::process_events() {
 		*/
 	}
 
-	Input::get_singleton()->flush_accumulated_events();
+	Input::get_singleton()->flush_buffered_events();
 }
 
 void DisplayServerX11::release_rendering_thread() {

platform/osx/display_server_osx.mm

@@ -3331,7 +3331,7 @@ void DisplayServerOSX::process_events() {
 
 	if (!drop_events) {
 		_process_key_events();
-		Input::get_singleton()->flush_accumulated_events();
+		Input::get_singleton()->flush_buffered_events();
 	}
 
 	for (Map<WindowID, WindowData>::Element *E = windows.front(); E; E = E->next()) {

platform/windows/display_server_windows.cpp

@@ -1527,7 +1527,7 @@ void DisplayServerWindows::process_events() {
 
 	if (!drop_events) {
 		_process_key_events();
-		Input::get_singleton()->flush_accumulated_events();
+		Input::get_singleton()->flush_buffered_events();
 	}
 }