From fe11219a0cf9f9a227532d9e839cd4c35e824c5d Mon Sep 17 00:00:00 2001
From: Xaver Hugl <xaver.hugl@gmail.com>
Date: Sat, 26 Jun 2021 01:00:56 +0200
Subject: [PATCH] improve gesture recognition

In order to not make misdetections with sub-pixel movements the gesture
recognizer completely ignored those. This fails however when you move
your fingers very slowly, so instead accumulate the delta and only use
it for direction detection if it's high enough.
---
 src/gestures.cpp | 26 +++++++++++++++++++-------
 src/gestures.h   |  2 ++
 2 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/src/gestures.cpp b/src/gestures.cpp
index 7839e2eba4..72e2c619f9 100644
--- a/src/gestures.cpp
+++ b/src/gestures.cpp
@@ -142,24 +142,30 @@ int GestureRecognizer::startSwipeGesture(uint fingerCount, const QPointF &startP
 void GestureRecognizer::updateSwipeGesture(const QSizeF &delta)
 {
     m_swipeUpdates << delta;
-    if (std::abs(delta.width()) < 1 && std::abs(delta.height()) < 1) {
-        // some (touch) devices report sub-pixel movement on screen edges
-        // this often cancels gestures -> ignore these movements
+    m_currentDelta += delta;
+    // with high resolution touch(pad) gestures can be cancelled without intention
+    // -> don't cancel movements if their accumulated values are too small but also still update the gesture for animations
+    if (std::abs(m_currentDelta.width()) > 1 || std::abs(m_currentDelta.height()) > 1) {
+        m_lastDelta = m_currentDelta;
+        m_currentDelta = QSizeF(0, 0);
+    } else if (std::abs(m_lastDelta.width()) < 1 && std::abs(m_lastDelta.height()) < 1) {
+        // no direction yet
         return;
     }
+
     // determine the direction of the swipe
-    if (delta.width() == delta.height()) {
+    if (m_lastDelta.width() == m_lastDelta.height()) {
         // special case of diagonal, this is not yet supported, thus cancel all gestures
         cancelActiveSwipeGestures();
         return;
     }
     SwipeGesture::Direction direction;
-    if (std::abs(delta.width()) > std::abs(delta.height())) {
+    if (std::abs(m_lastDelta.width()) > std::abs(m_lastDelta.height())) {
         // horizontal
-        direction = delta.width() < 0 ? SwipeGesture::Direction::Left : SwipeGesture::Direction::Right;
+        direction = m_lastDelta.width() < 0 ? SwipeGesture::Direction::Left : SwipeGesture::Direction::Right;
     } else {
         // vertical
-        direction = delta.height() < 0 ? SwipeGesture::Direction::Up : SwipeGesture::Direction::Down;
+        direction = m_lastDelta.height() < 0 ? SwipeGesture::Direction::Up : SwipeGesture::Direction::Down;
     }
     const QSizeF combinedDelta = std::accumulate(m_swipeUpdates.constBegin(), m_swipeUpdates.constEnd(), QSizeF(0, 0));
     for (auto it = m_activeSwipeGestures.begin(); it != m_activeSwipeGestures.end();) {
@@ -182,12 +188,16 @@ void GestureRecognizer::cancelActiveSwipeGestures()
         Q_EMIT g->cancelled();
     }
     m_activeSwipeGestures.clear();
+    m_currentDelta = QSizeF(0, 0);
+    m_lastDelta = QSizeF(0, 0);
 }
 
 void GestureRecognizer::cancelSwipeGesture()
 {
     cancelActiveSwipeGestures();
     m_swipeUpdates.clear();
+    m_currentDelta = QSizeF(0, 0);
+    m_lastDelta = QSizeF(0, 0);
 }
 
 void GestureRecognizer::endSwipeGesture()
@@ -202,6 +212,8 @@ void GestureRecognizer::endSwipeGesture()
     }
     m_activeSwipeGestures.clear();
     m_swipeUpdates.clear();
+    m_currentDelta = QSizeF(0, 0);
+    m_lastDelta = QSizeF(0, 0);
 }
 
 }
diff --git a/src/gestures.h b/src/gestures.h
index 9fc2fadc3e..eed5ced5b0 100644
--- a/src/gestures.h
+++ b/src/gestures.h
@@ -201,6 +201,8 @@ private:
     QVector<Gesture*> m_activeSwipeGestures;
     QMap<Gesture*, QMetaObject::Connection> m_destroyConnections;
     QVector<QSizeF> m_swipeUpdates;
+    QSizeF m_lastDelta = QSizeF(0, 0);
+    QSizeF m_currentDelta = QSizeF(0, 0);
 };
 
 }