Qt Reference Documentation

# knob.cpp Example File

touch/knobs/knob.cpp

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     #include "knob.h"

     #include <QBrush>
     #include <QTouchEvent>

     Knob::Knob()
         : QGraphicsEllipseItem(-50, -50, 100, 100)
     {
         setAcceptTouchEvents(true);
         setBrush(Qt::lightGray);

         QGraphicsEllipseItem *leftItem = new QGraphicsEllipseItem(0, 0, 20, 20, this);
         leftItem->setPos(-40, -10);
         leftItem->setBrush(Qt::darkGreen);

         QGraphicsEllipseItem *rightItem = new QGraphicsEllipseItem(0, 0, 20, 20, this);
         rightItem->setPos(20, -10);
         rightItem->setBrush(Qt::darkRed);
     }

     bool Knob::sceneEvent(QEvent *event)
     {
         switch (event->type()) {
         case QEvent::TouchBegin:
         case QEvent::TouchUpdate:
         case QEvent::TouchEnd:
         {
             QTouchEvent *touchEvent = static_cast<QTouchEvent *>(event);

             if (touchEvent->touchPoints().count() == 2) {
                 const QTouchEvent::TouchPoint &touchPoint1 = touchEvent->touchPoints().first();
                 const QTouchEvent::TouchPoint &touchPoint2 = touchEvent->touchPoints().last();

                 QLineF line1(touchPoint1.lastScenePos(), touchPoint2.lastScenePos());
                 QLineF line2(touchPoint1.scenePos(), touchPoint2.scenePos());

                 rotate(line2.angleTo(line1));
             }

             break;
         }

         default:
             return QGraphicsItem::sceneEvent(event);
         }

         return true;
     }