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;
  }