knob.cpp Example File | Qt Widgets 5.12.4

Qt 5.12 | Qt Widgets | Touch Knobs Example | knob.cpp Example File

Qt 5.12.4 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());

                  setTransform(QTransform().rotate(line2.angleTo(line1)), true);
              }

              break;
          }

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

          return true;
      }