QSwipeGestureRecognizer: Allow for small direction changes.

When trying to do a straight right/left/up/down swipe, a minimal
change in the other direction caused to the gesture to be canceled.
Introduce a threshold for checking such to prevent this.

Task-number: QTBUG-46195
Change-Id: I3e199f2ec0c81d23a16073b1f5b8fff004958239
Reviewed-by: Shawn Rutledge <shawn.rutledge@theqtcompany.com>

2 files changed, 26 insertions, 13 deletions

diff --git a/src/widgets/kernel/qstandardgestures.cpp b/src/widgets/kernel/qstandardgestures.cpp
index d19e473d18..3d6ae3f322 100644
--- a/src/widgets/kernel/qstandardgestures.cpp
+++ b/src/widgets/kernel/qstandardgestures.cpp
@@ -334,23 +334,27 @@ QGestureRecognizer::Result QSwipeGestureRecognizer::recognize(QGesture *state,
             d->swipeAngle = QLineF(p1.startScreenPos(), p1.screenPos()).angle();
 
             static const int MoveThreshold = 50;
+            static const int directionChangeThreshold = MoveThreshold / 8;
             if (qAbs(xDistance) > MoveThreshold || qAbs(yDistance) > MoveThreshold) {
                 // measure the distance to check if the direction changed
                 d->lastPositions[0] = p1.screenPos().toPoint();
                 d->lastPositions[1] = p2.screenPos().toPoint();
                 d->lastPositions[2] = p3.screenPos().toPoint();
-                QSwipeGesture::SwipeDirection horizontal =
-                        xDistance > 0 ? QSwipeGesture::Right : QSwipeGesture::Left;
-                QSwipeGesture::SwipeDirection vertical =
-                        yDistance > 0 ? QSwipeGesture::Down : QSwipeGesture::Up;
-                if (d->verticalDirection == QSwipeGesture::NoDirection)
+                result = QGestureRecognizer::TriggerGesture;
+                // QTBUG-46195, small changes in direction should not cause the gesture to be canceled.
+                if (d->verticalDirection == QSwipeGesture::NoDirection || qAbs(yDistance) > directionChangeThreshold) {
+                    const QSwipeGesture::SwipeDirection vertical = yDistance > 0
+                        ? QSwipeGesture::Down : QSwipeGesture::Up;
+                    if (d->verticalDirection != QSwipeGesture::NoDirection && d->verticalDirection != vertical)
+                        result = QGestureRecognizer::CancelGesture;
                     d->verticalDirection = vertical;
-                if (d->horizontalDirection == QSwipeGesture::NoDirection)
+                }
+                if (d->horizontalDirection == QSwipeGesture::NoDirection || qAbs(xDistance) > directionChangeThreshold) {
+                    const QSwipeGesture::SwipeDirection horizontal = xDistance > 0
+                        ? QSwipeGesture::Right : QSwipeGesture::Left;
+                    if (d->horizontalDirection != QSwipeGesture::NoDirection && d->horizontalDirection != horizontal)
+                        result = QGestureRecognizer::CancelGesture;
                     d->horizontalDirection = horizontal;
-                if (d->verticalDirection != vertical || d->horizontalDirection != horizontal) {
-                    result = QGestureRecognizer::CancelGesture;
-                } else {
-                    result = QGestureRecognizer::TriggerGesture;
                 }
             } else {
                 if (q->state() != Qt::NoGesture)
diff --git a/tests/auto/widgets/gestures/qgesturerecognizer/tst_qgesturerecognizer.cpp b/tests/auto/widgets/gestures/qgesturerecognizer/tst_qgesturerecognizer.cpp
index 67c431d16e..dc2adad5da 100644
--- a/tests/auto/widgets/gestures/qgesturerecognizer/tst_qgesturerecognizer.cpp
+++ b/tests/auto/widgets/gestures/qgesturerecognizer/tst_qgesturerecognizer.cpp
@@ -269,7 +269,8 @@ void tst_QGestureRecognizer::pinchGesture()
 
 enum SwipeSubTest {
     SwipeLineSubTest,
-    SwipeChangeDirectionSubTest,
+    SwipeDirectionChangeSubTest,
+    SwipeSmallDirectionChangeSubTest
 };
 
 void tst_QGestureRecognizer::swipeGesture_data()
@@ -277,7 +278,8 @@ void tst_QGestureRecognizer::swipeGesture_data()
     QTest::addColumn<int>("swipeSubTest");
     QTest::addColumn<bool>("gestureExpected");
     QTest::newRow("Line") << int(SwipeLineSubTest) << true;
-    QTest::newRow("ChangeDirection") << int(SwipeChangeDirectionSubTest) << false;
+    QTest::newRow("DirectionChange") << int(SwipeDirectionChangeSubTest) << false;
+    QTest::newRow("SmallDirectionChange") << int(SwipeSmallDirectionChangeSubTest) << true;
 }
 
 void tst_QGestureRecognizer::swipeGesture()
@@ -314,10 +316,17 @@ void tst_QGestureRecognizer::swipeGesture()
     case SwipeLineSubTest:
         linearSequence(5, moveDelta, swipeSequence, points, &widget);
         break;
-    case SwipeChangeDirectionSubTest:
+    case SwipeDirectionChangeSubTest:
         linearSequence(5, moveDelta, swipeSequence, points, &widget);
         linearSequence(3, QPoint(-moveDelta.x(), moveDelta.y()), swipeSequence, points, &widget);
         break;
+    case SwipeSmallDirectionChangeSubTest: { // QTBUG-46195, small changes in direction should not cause the gesture to be canceled.
+        const QPoint smallChangeMoveDelta(50, 1);
+        linearSequence(5, smallChangeMoveDelta, swipeSequence, points, &widget);
+        linearSequence(1, QPoint(smallChangeMoveDelta.x(), -3), swipeSequence, points, &widget);
+        linearSequence(5, smallChangeMoveDelta, swipeSequence, points, &widget);
+    }
+        break;
     }
 
     releaseSequence(swipeSequence, points, &widget);