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Thread: Qt 6: Simulating Multi-Touch (Pan & Zoom) - Migration from Qt 5

  1. 19th February 2025, 08:48 #1
    Kaviara
    Kaviara is offline Beginner
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    Default Qt 6: Simulating Multi-Touch (Pan & Zoom) - Migration from Qt 5

    I am developing a Qt 6.8 touch-based application where an Android client sends touch data to a Windows server application. The Windows server receives multi-touch data and needs to simulate touch events for pan and zoom gestures.
    Issue:
    Previously, in Qt 5, the following code worked perfectly using QTouchEvent with direct setters to simulate multi-touch gestures:
    Qt 5 Working Code:

    Qt Code: 
    1. struct TouchPoint {
    2.      int id;
    3.      short posX, posY;
    4.      short lastPosX, lastPosY;
    5.      short startPosX, startPosY;
    6.      int state;
    7.      unsigned short pressure;   // 0 to 65535.
    8.  };    
    9.  
    10. void simulateTouch (const TouchPacket *packet)
    11. {
    12.     const TouchPacket::e_touchType type = packet->touchType();
    13.     const Qt::TouchPointStates states = static_cast<Qt::TouchPointStates>(packet->touchStates());
    14.     const Qt::KeyboardModifiers modifiers = packet->getQtModifiers();
    15.  
    16.     const int numPoints = static_cast<int> ( packet->touchPoints().size() );
    17.     QList< QTouchEvent::TouchPoint > points;
    18.     points.reserve( numPoints );
    19.  
    20.     const int width  = this->mainWindow->width();
    21.     const int height = this->mainWindow->height();
    22.     QWidget *parent = this->mainWindow;
    23.     while (parent->parentWidget() != 0) {
    24.         parent = parent->parentWidget();
    25.     }
    26.     // need the position of the top level widget (position is relative to desktop and not parent widget)
    27.     const QPoint pos = parent->pos();
    28.  
    29.     for (int i(0); i<numPoints; ++i) {
    30.         const TouchPacket::TouchPoint & pkPoint(  packet->touchPoints()[i] );
    31.  
    32.         nextPt.setRect (QRectF());
    33.         nextPt.setScreenRect (QRectF());
    34.  
    35.         nextPt.setNormalizedPos(QPointF(pkPoint.posX / qreal(width), pkPoint.posY / qreal(height)));
    36.         nextPt.setLastNormalizedPos(QPointF(pkPoint.lastPosX / qreal(width), pkPoint.lastPosY / qreal(height)));
    37.         nextPt.setStartNormalizedPos(QPointF(pkPoint.startPosX / qreal(width), pkPoint.startPosY / qreal(height)));
    38.  
    39.         nextPt.setPos( QPointF(pkPoint.posX, pkPoint.posY) );
    40.         nextPt.setScenePos (nextPt.pos());
    41.         nextPt.setScreenPos(pos + nextPt.pos());
    42.  
    43.         nextPt.setLastPos( QPointF(pkPoint.lastPosX, pkPoint.lastPosY));
    44.         nextPt.setLastScenePos (nextPt.lastPos());
    45.         nextPt.setLastScreenPos(pos + nextPt.lastPos());
    46.  
    47.         nextPt.setStartPos(QPointF(pkPoint.startPosX, pkPoint.startPosY));
    48.         nextPt.setStartScenePos(nextPt.startPos());
    49.         nextPt.setStartScreenPos(pos + nextPt.startPos());
    50.  
    51.         nextPt.setPressure( 1.0 ); //((double)pkPoint.pressure ) / 65535. ) ;
    52.  
    53.         nextPt.setState (static_cast<Qt::TouchPointStates>(pkPoint.state));
    54.  
    55.         points.push_back(nextPt);
    56.  
    57.         //qDebug() << nextPt.pos() << nextPt.normalizedPos() << nextPt.state() << nextPt.pressure() << nextPt.screenRect();
    58.     }
    59.  
    60.     QTouchEvent * tevent = NULL;
    61.  
    62.     switch (type) {
    63.     case TouchPacket::TouchBegin:
    64.         tevent = new QTouchEvent( QEvent::TouchBegin, &this->touchDevice, modifiers, states, points );
    65.         break;
    66.     case TouchPacket::TouchCancel:
    67.         tevent = new QTouchEvent( QEvent::TouchCancel, &this->touchDevice, modifiers, states, points );
    68.         break;
    69.     case TouchPacket::TouchEnd:
    70.         tevent = new QTouchEvent( QEvent::TouchEnd, &this->touchDevice, modifiers, states, points );
    71.         break;
    72.     case TouchPacket::TouchUpdate:
    73.         tevent = new QTouchEvent( QEvent::TouchUpdate, &this->touchDevice, modifiers, states, points );
    74.         break;
    75.     default:
    76.         qWarning() << "Unknown touch packet" << type;
    77.     }
    78.  
    79.     if (tevent) {
    80.         // The post event queue will take ownership of the event and delete it once it has been posted
    81.         QWidget *currentWidget = this->mainWindow->childAt (points.at(0).pos().toPoint());
    82.         //qDebug() << "posting to" << currentWidget << "with" << tevent->touchPoints().count() << "points" << states;
    83.         QApplication::postEvent (currentWidget, tevent);
    84.     }
    85. }
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    Problem in Qt 6:
    After migrating to Qt 6, QTouchEvent::TouchPoint and its setters are no longer available. Instead, Qt 6 uses QEventPoint and QMutableEventPoint, but only a few setters are available in QMutableEventPoint.
    I receive touch data in the following struct from the client:

    Qt Code: 
    1. struct TouchPoint {
    2.     int id;
    3.     short posX, posY;
    4.     short lastPosX, lastPosY;
    5.     short startPosX, startPosY;
    6.     int state;
    7.     unsigned short pressure; // 0 to 65535
    8. };
    To copy to clipboard, switch view to plain text mode 

    I attempted to migrate the Qt 5 code using QEventPoint but ran into issues:
    Attempted Qt 6 Migration Code:

    Qt Code: 
    1. void simulateTouch (const TouchPacket *packet)
    2. {
    3.     const TouchPacket::e_touchType type = packet->touchType();
    4.     const Qt::TouchPointStates states = static_cast<Qt::TouchPointStates>(packet->touchStates());
    5.     const Qt::KeyboardModifiers modifiers = packet->getQtModifiers();
    6.  
    7.     const int numPoints = static_cast<int> ( packet->touchPoints().size() );
    8.     QList< QTouchEvent::TouchPoint > points;
    9.     points.reserve( numPoints );
    10.  
    11.     const int width  = this->mainWindow->width();
    12.     const int height = this->mainWindow->height();
    13.     QWidget *parent = this->mainWindow;
    14.     while (parent->parentWidget() != 0) {
    15.         parent = parent->parentWidget();
    16.     }
    17.     // need the position of the top level widget (position is relative to desktop and not parent widget)
    18.     const QPoint pos = parent->pos();
    19.  
    20.     for (int i(0); i<numPoints; ++i) {
    21.         const TouchPacket::TouchPoint & pkPoint(  packet->touchPoints()[i] );
    22.         QTouchEvent::TouchPoint nextPt( pkPoint.id );
    23.  
    24.  
    25.  
    26.         // Assign state based on touch type
    27.         QEventPoint::State pointState = QEventPoint::State::Unknown;
    28.         switch (type) {
    29.         case TouchPacket::TouchBegin:
    30.             pointState = QEventPoint::State::Pressed;
    31.             break;
    32.         case TouchPacket::TouchUpdate:
    33.             pointState = QEventPoint::State::Updated;
    34.             break;
    35.         case TouchPacket::TouchEnd:
    36.             pointState = QEventPoint::State::Released;
    37.             break;
    38.         case TouchPacket::TouchCancel:
    39.             pointState = QEventPoint::State::Stationary;
    40.             break;
    41.         default:
    42.             break;
    43.         }
    44.  
    45.         QEventPoint nextPtNew(pkPoint.id, pointState, QPointF(pkPoint.posX, pkPoint.posY),
    46.                                 QPointF(pkPoint.posX + pos.x(), pkPoint.posY + pos.y()));
    47.  
    48.  
    49.         QMutableEventPoint::setPressure(nextPtNew, pkPoint.pressure);
    50.         QMutableEventPoint::setState(nextPtNew, pointState);
    51.         QMutableEventPoint::setGlobalLastPosition(nextPtNew, QPointF(pkPoint.posX + pos.x(), pkPoint.posY + pos.y()));
    52.         QMutableEventPoint::setScenePosition(nextPtNew, QPointF(pkPoint.posX + pos.x(), pkPoint.posY + pos.y()));
    53.  
    54.         points.push_back(nextPtNew);
    55.     }
    56.  
    57.     QTouchEvent * tevent = NULL;
    58.  
    59.     switch (type) {
    60.     case TouchPacket::TouchBegin:
    61.         //tevent = new QTouchEvent( QEvent::TouchBegin, &this->touchDevice, modifiers, states, points );
    62.         tevent = new QTouchEvent(QEvent::TouchBegin, &this->touchDevice, modifiers, points);
    63.         break;
    64.     case TouchPacket::TouchCancel:
    65.         //tevent = new QTouchEvent( QEvent::TouchCancel, &this->touchDevice, modifiers, states, points );
    66.         tevent = new QTouchEvent(QEvent::TouchCancel, &this->touchDevice, modifiers, points);
    67.         break;
    68.     case TouchPacket::TouchEnd:
    69.         //tevent = new QTouchEvent( QEvent::TouchEnd, &this->touchDevice, modifiers, states, points );
    70.         tevent = new QTouchEvent(QEvent::TouchEnd, &this->touchDevice, modifiers, points);
    71.         break;
    72.     case TouchPacket::TouchUpdate:
    73.         //tevent = new QTouchEvent( QEvent::TouchUpdate, &this->touchDevice, modifiers, states, points );
    74.         tevent = new QTouchEvent(QEvent::TouchUpdate, &this->touchDevice, modifiers, points);
    75.         break;
    76.     default:
    77.         qWarning() << "Unknown touch packet" << type;
    78.     }
    79.  
    80.     if (tevent && !points.isEmpty()) {
    81.         // The post event queue will take ownership of the event and delete it once it has been posted
    82.         QWidget *currentWidget = this->mainWindow->childAt (points.at(0).pos().toPoint());
    83.         //qDebug() << "posting to" << currentWidget << "with" << tevent->touchPoints().count() << "points" << states;
    84.         QApplication::postEvent (currentWidget, tevent);
    85.     }
    86. }
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    Questions:
    • How can I correctly migrate my Qt 5 touch event simulation code to Qt 6?
    • What is the correct way to construct and append QMutableEventPoint to QPointerEvent?
    • Are there additional event properties I need to set to ensure continuous pan and zoom gestures?
    • Is there a recommended approach to simulate multi-touch gestures like pan and zoom in Qt 6?
      Need alternative setters / ways for the below API
      Qt Code: 
      1. QTouchEvent::TouchPoint nextPt( pkPoint.id );
      2. nextPt.setRect (QRectF());
      3. nextPt.setScreenRect (QRectF());
      4. nextPt.setNormalizedPos(QPointF(pkPoint.posX / qreal(width), pkPoint.posY / qreal(height)));
      5. nextPt.setLastNormalizedPos(QPointF(pkPoint.lastPosX / qreal(width), pkPoint.lastPosY / qreal(height)));
      6. nextPt.setStartNormalizedPos(QPointF(pkPoint.startPosX / qreal(width), pkPoint.startPosY / qreal(height)));
      7. nextPt.setPos( QPointF(pkPoint.posX, pkPoint.posY) );
      8. nextPt.setScenePos (nextPt.pos());
      9. nextPt.setScreenPos(pos + nextPt.pos());
      10. nextPt.setLastPos( QPointF(pkPoint.lastPosX, pkPoint.lastPosY));
      11. nextPt.setLastScenePos (nextPt.lastPos());
      12. nextPt.setLastScreenPos(pos + nextPt.lastPos());
      13. nextPt.setStartPos(QPointF(pkPoint.startPosX, pkPoint.startPosY));
      14. nextPt.setStartScenePos(nextPt.startPos());
      15. nextPt.setStartScreenPos(pos + nextPt.startPos());
      To copy to clipboard, switch view to plain text mode 
    • Any guidance on this migration process would be highly appreciated!
    Last edited by Kaviara; 19th February 2025 at 13:27. Reason: spelling corrections
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