From ca45aca406b79474392771f73bb4094a859ac771 Mon Sep 17 00:00:00 2001
From: abc def <24701-abcdef@users.noreply.gitlab.freedesktop.org>
Date: Mon, 7 Feb 2022 15:44:00 +0100
Subject: [PATCH] Debounce for 4+ fingers before drag starts

When the drag hasn't started there's now a 50 ms debounce time
to disambiguate from 4+ finger gestures.
---
 src/evdev-mt-touchpad-tfd.c | 89 +++++++++++++++++++++++++++++++++----
 src/evdev-mt-touchpad.h     |  6 ++-
 2 files changed, 85 insertions(+), 10 deletions(-)

diff --git a/src/evdev-mt-touchpad-tfd.c b/src/evdev-mt-touchpad-tfd.c
index c1c32862..d9a27c8a 100644
--- a/src/evdev-mt-touchpad-tfd.c
+++ b/src/evdev-mt-touchpad-tfd.c
@@ -42,7 +42,8 @@ tfd_state_to_str(enum tp_tfd_state state)
 {
 	switch(state) {
 	CASE_RETURN_STRING(TFD_STATE_IDLE);
-	CASE_RETURN_STRING(TFD_STATE_POSSIBLE_DRAG);
+	CASE_RETURN_STRING(TFD_STATE_POSSIBLE_BEGIN);
+	CASE_RETURN_STRING(TFD_STATE_AWAIT_DRAG);
 	CASE_RETURN_STRING(TFD_STATE_DRAG);
 	CASE_RETURN_STRING(TFD_STATE_POSSIBLE_ZERO_FINGERS);
 	CASE_RETURN_STRING(TFD_STATE_AWAIT_RESUME);
@@ -239,8 +240,9 @@ tp_tfd_idle_handle_event(struct tp_dispatch *tp,
 	case TFD_EVENT_TOUCH_COUNT_INCREASE:
 	case TFD_EVENT_TOUCH_COUNT_DECREASE:
 		if (nfingers_down == 3) {
-			tp->tfd.state = TFD_STATE_POSSIBLE_DRAG;
-			tp_tfd_set_button_press_delay_timer(tp, time);
+			tp->tfd.state = TFD_STATE_POSSIBLE_BEGIN;
+			// tp_tfd_set_button_press_delay_timer(tp, time);
+			tp_tfd_set_await_more_fingers_timer(tp, time);
 		}
 		break;
 	case TFD_EVENT_MOTION:
@@ -255,6 +257,72 @@ tp_tfd_idle_handle_event(struct tp_dispatch *tp,
 	}
 }
 
+
+
+
+
+/* Waiting for more fingers. Three fingers have been detected, but it might be 
+a transitory phase towards 4 or more fingers, which should not begin the
+drag. */
+static void
+tp_tfd_possible_begin_handle_event(struct tp_dispatch *tp,
+				  struct tp_touch *t,
+				  enum tfd_event event, uint64_t time,
+				   int nfingers_down)
+{
+	switch (event) {
+	case TFD_EVENT_TOUCH_COUNT_INCREASE:
+		switch (nfingers_down) {
+		case 0: 
+		case 1:
+		case 2:
+		case 3:
+			break; // bug?
+		default:
+			tp_tfd_unpin_fingers(tp);
+			tp->tfd.state = TFD_STATE_IDLE;
+			tp_tfd_clear_timer(tp);
+			break;
+		}
+		break;
+	case TFD_EVENT_MOTION:
+		break;
+	case TFD_EVENT_RESUME_TIMEOUT: 
+		break; // bug
+	case TFD_EVENT_TOUCH_COUNT_DECREASE:
+		/* a decrease forces immediate evaluation as if the timer had fired */
+		tp_tfd_clear_timer(tp);
+		/* fallthrough */
+	case TFD_EVENT_TIMEOUT:
+		/* time to check whether we have 3 fingers touching */
+		switch (nfingers_down) {
+		case 0:
+		case 1:
+		case 2:
+		default:
+			tp_tfd_unpin_fingers(tp);
+			tp->tfd.state = TFD_STATE_IDLE;
+			break;
+		case 3:
+			tp_tfd_unpin_fingers(tp);
+			// TODO: compensate for the duration of this state 
+			tp_tfd_set_button_press_delay_timer(tp, time);
+			tp->tfd.state = TFD_STATE_AWAIT_DRAG;
+			break;
+		}
+		break;
+	case TFD_EVENT_TAP:
+	case TFD_EVENT_BUTTON:
+		tp_tfd_unpin_fingers(tp);
+		tp->tfd.state = TFD_STATE_IDLE;
+		tp_tfd_clear_timer(tp);
+		break;
+	}
+}
+
+
+
+
 /* finishes hold gestures and cancels other gestures */
 static void
 tp_tfd_interrupt_gestures(struct tp_dispatch *tp, struct tp_touch *t, uint64_t time)
@@ -280,7 +348,7 @@ tp_tfd_interrupt_gestures(struct tp_dispatch *tp, struct tp_touch *t, uint64_t t
 /* We don't have the primary button pressed in this state; the 
 press is delayed if the fingers have remained stationary */
 static void
-tp_tfd_possible_drag_handle_event(struct tp_dispatch *tp,
+tp_tfd_await_drag_handle_event(struct tp_dispatch *tp,
 			      struct tp_touch *t,
 			      enum tfd_event event, uint64_t time, int nfingers_down)
 {	
@@ -754,8 +822,12 @@ tp_tfd_handle_event(struct tp_dispatch *tp,
 		tp_tfd_idle_handle_event(tp, t, event, time, nfingers_down);
 		break;
 		
-	case TFD_STATE_POSSIBLE_DRAG:
-		tp_tfd_possible_drag_handle_event(tp, t, event, time, nfingers_down);
+	case TFD_STATE_POSSIBLE_BEGIN:
+		tp_tfd_possible_begin_handle_event(tp, t, event, time, nfingers_down);
+		break;
+
+	case TFD_STATE_AWAIT_DRAG:
+		tp_tfd_await_drag_handle_event(tp, t, event, time, nfingers_down);
 		break;
 
 	case TFD_STATE_DRAG:
@@ -826,7 +898,7 @@ tp_tfd_exceeds_motion_threshold(struct tp_dispatch *tp,
 		return false;
 
 	double threshold = DEFAULT_TFD_MOVE_THRESHOLD;
-	if (tp->tfd.state == TFD_STATE_POSSIBLE_DRAG) {
+	if (tp->tfd.state == TFD_STATE_AWAIT_DRAG) {
 		// TODO: have to figure out something better
 		// MOTION events are too decoupled from what's required to actually move
 		// the cursor. TODO: look it up
@@ -967,7 +1039,8 @@ tp_tfd_handle_tap(struct tp_dispatch *tp, uint64_t time)
 			tp_tfd_handle_event(tp, NULL, TFD_EVENT_TAP, time, tp->tfd.finger_count);
 			break;
 		case TFD_STATE_IDLE:
-		case TFD_STATE_POSSIBLE_DRAG:
+		case TFD_STATE_POSSIBLE_BEGIN:
+		case TFD_STATE_AWAIT_DRAG:
 		case TFD_STATE_DRAG:
 			break;
 	}
diff --git a/src/evdev-mt-touchpad.h b/src/evdev-mt-touchpad.h
index ddcbe2e3..09268602 100644
--- a/src/evdev-mt-touchpad.h
+++ b/src/evdev-mt-touchpad.h
@@ -141,8 +141,10 @@ enum tp_tfd_state {
 
 	/* waiting for 3 fingers */
 	TFD_STATE_IDLE,
-	/* 3 fingers touching, possible 4+ f gesture */
-	TFD_STATE_POSSIBLE_DRAG,
+	/* [debounce] disambiguate between starting a drag and a possible 4+ gesture */
+	TFD_STATE_POSSIBLE_BEGIN,
+	/* 3 fingers touching, waiting for motion or timeout */
+	TFD_STATE_AWAIT_DRAG,
 	/* 3 fingers touching and button press has been output */
 	TFD_STATE_DRAG,
 	/* [debounce] drag-lock; 1 finger touching, possibly going to 0 fingers */