Handle "interesting" stationary touchpoints as if they moved

Qt Quick will not receive "uninteresting" stationary touchpoints, but
only those in which some property has changed. So MultiPointTouchArea
should react to stationary touchpoints in the same way as if they moved,
so that UIs can react to changes in touchpoint velocity, pressure etc.
And QQuickWindow has to be willing to delivery stationary touchpoints
to make this possible. However when a QTouchEvent is customized for
delivery to a specific Item, by including only the touchpoints that
are inside the Item, then if those touchpoints are all stationary,
the event only needs to be delivered if at least one of them is
an "interesting" stationary touchpoint. So we need to depend on
a new per-touchpoint flag that QGuiApplication will set when it
discovers that some property of the touchpoint has changed. That is
QTouchEventTouchPointPrivate::stationaryWithModifiedProperty.

Fixes: QTBUG-77142
Change-Id: I763d56ff55c048b258dca40d88283ed016447c35
Reviewed-by: Jan Arve Sæther <jan-arve.saether@qt.io>
(cherry picked from commit ae346195efaca5d01b67c5df1209512c7edaddb0)
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

2 files changed, 9 insertions, 2 deletions

diff --git a/src/quick/items/qquickevents.cpp b/src/quick/items/qquickevents.cpp
index 8303c3fed1..4299f28955 100644
--- a/src/quick/items/qquickevents.cpp
+++ b/src/quick/items/qquickevents.cpp
@@ -41,6 +41,7 @@
 #include <QtCore/qmap.h>
 #include <QtGui/private/qguiapplication_p.h>
 #include <QtGui/private/qtouchdevice_p.h>
+#include <QtGui/private/qevent_p.h>
 #include <QtQuick/private/qquickitem_p.h>
 #include <QtQuick/private/qquickpointerhandler_p.h>
 #include <QtQuick/private/qquickwindow_p.h>
@@ -1828,6 +1829,7 @@ QTouchEvent *QQuickPointerTouchEvent::touchEventForItem(QQuickItem *item, bool i
     // but that would require changing tst_qquickwindow::touchEvent_velocity(): it expects transformed velocity
 
     bool anyPressOrReleaseInside = false;
+    bool anyStationaryWithModifiedPropertyInside = false;
     bool anyGrabber = false;
     QMatrix4x4 transformMatrix(QQuickItemPrivate::get(item)->windowToItemTransform());
     for (int i = 0; i < m_pointCount; ++i) {
@@ -1860,6 +1862,8 @@ QTouchEvent *QQuickPointerTouchEvent::touchEventForItem(QQuickItem *item, bool i
             anyPressOrReleaseInside = true;
         const QTouchEvent::TouchPoint *tp = touchPointById(p->pointId());
         if (tp) {
+            if (isInside && tp->d->stationaryWithModifiedProperty)
+                anyStationaryWithModifiedPropertyInside = true;
             eventStates |= tp->state();
             QTouchEvent::TouchPoint tpCopy = *tp;
             tpCopy.setPos(item->mapFromScene(tpCopy.scenePos()));
@@ -1873,7 +1877,8 @@ QTouchEvent *QQuickPointerTouchEvent::touchEventForItem(QQuickItem *item, bool i
 
     // Now touchPoints will have only points which are inside the item.
     // But if none of them were just pressed inside, and the item has no other reason to care, ignore them anyway.
-    if (eventStates == Qt::TouchPointStationary || touchPoints.isEmpty() || (!anyPressOrReleaseInside && !anyGrabber && !isFiltering))
+    if ((eventStates == Qt::TouchPointStationary && !anyStationaryWithModifiedPropertyInside) ||
+            touchPoints.isEmpty() || (!anyPressOrReleaseInside && !anyGrabber && !isFiltering))
         return nullptr;
 
     // if all points have the same state, set the event type accordingly
diff --git a/src/quick/items/qquickmultipointtoucharea.cpp b/src/quick/items/qquickmultipointtoucharea.cpp
index 3eca535a67..708cfff76b 100644
--- a/src/quick/items/qquickmultipointtoucharea.cpp
+++ b/src/quick/items/qquickmultipointtoucharea.cpp
@@ -40,6 +40,7 @@
 #include "qquickmultipointtoucharea_p.h"
 #include <QtQuick/qquickwindow.h>
 #include <private/qsgadaptationlayer_p.h>
+#include <private/qevent_p.h>
 #include <private/qquickitem_p.h>
 #include <private/qguiapplication_p.h>
 #include <QEvent>
@@ -655,7 +656,8 @@ void QQuickMultiPointTouchArea::updateTouchData(QEvent *event)
                 // (we may have just obtained enough points to start tracking them -- in that case moved or stationary count as newly pressed)
                 addTouchPoint(&p);
                 started = true;
-            } else if (touchPointState & Qt::TouchPointMoved) {
+            } else if ((touchPointState & Qt::TouchPointMoved) || p.d->stationaryWithModifiedProperty) {
+                // React to a stationary point with a property change (velocity, pressure) as if the point moved. (QTBUG-77142)
                 QQuickTouchPoint* dtp = static_cast<QQuickTouchPoint*>(_touchPoints.value(id));
                 Q_ASSERT(dtp);
                 _movedTouchPoints.append(dtp);