Track screen drag speed

Following the universal input handling effort, this works the same for every platform, as long as the touch move event coming from it contains the relative movement.

The same tracking algorithm used to track the mouse speed is used here, but tracking separately each touch index.

Fixes #3623.

2 files changed, 31 insertions, 5 deletions

diff --git a/main/input_default.cpp b/main/input_default.cpp
index 913c143025..33c422190d 100644
--- a/main/input_default.cpp
+++ b/main/input_default.cpp
@@ -261,6 +261,13 @@ void InputDefault::parse_input_event(const Ref<InputEvent> &p_event) {
 
 void InputDefault::_parse_input_event_impl(const Ref<InputEvent> &p_event, bool p_is_emulated) {
 
+	// Notes on mouse-touch emulation:
+	// - Emulated mouse events are parsed, that is, re-routed to this method, so they make the same effects
+	//   as true mouse events. The only difference is the situation is flagged as emulated so they are not
+	//   emulated back to touch events in an endless loop.
+	// - Emulated touch events are handed right to the main loop (i.e., the SceneTree) because they don't
+	//   require additional handling by this class.
+
 	_THREAD_SAFE_METHOD_
 
 	Ref<InputEventKey> k = p_event;
@@ -316,11 +323,21 @@ void InputDefault::_parse_input_event_impl(const Ref<InputEvent> &p_event, bool
 		}
 	}
 
-	if (emulate_mouse_from_touch) {
+	Ref<InputEventScreenTouch> st = p_event;
+
+	if (st.is_valid()) {
+
+		if (st->is_pressed()) {
+			SpeedTrack &track = touch_speed_track[st->get_index()];
+			track.reset();
+		} else {
+			// Since a pointer index may not occur again (OSs may or may not reuse them),
+			// imperatively remove it from the map to keep no fossil entries in it
+			touch_speed_track.erase(st->get_index());
+		}
 
-		Ref<InputEventScreenTouch> st = p_event;
+		if (emulate_mouse_from_touch) {
 
-		if (st.is_valid()) {
 			bool translate = false;
 			if (st->is_pressed()) {
 				if (mouse_from_touch_index == -1) {
@@ -351,10 +368,18 @@ void InputDefault::_parse_input_event_impl(const Ref<InputEvent> &p_event, bool
 				_parse_input_event_impl(button_event, true);
 			}
 		}
+	}
+
+	Ref<InputEventScreenDrag> sd = p_event;
+
+	if (sd.is_valid()) {
+
+		SpeedTrack &track = touch_speed_track[sd->get_index()];
+		track.update(sd->get_relative());
+		sd->set_speed(track.speed);
 
-		Ref<InputEventScreenDrag> sd = p_event;
+		if (emulate_mouse_from_touch && sd->get_index() == mouse_from_touch_index) {
 
-		if (sd.is_valid() && sd->get_index() == mouse_from_touch_index) {
 			Ref<InputEventMouseMotion> motion_event;
 			motion_event.instance();
 
diff --git a/main/input_default.h b/main/input_default.h
index b420ec124b..4964b9a83c 100644
--- a/main/input_default.h
+++ b/main/input_default.h
@@ -117,6 +117,7 @@ class InputDefault : public Input {
 	};
 
 	SpeedTrack mouse_speed_track;
+	Map<int, SpeedTrack> touch_speed_track;
 	Map<int, Joypad> joy_names;
 	int fallback_mapping;