Qt Reference Documentation

# graphicsview.cpp Example File

touch/pinchzoom/graphicsview.cpp

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     #include "graphicsview.h"

     #include <QScrollBar>
     #include <QTouchEvent>

     GraphicsView::GraphicsView(QGraphicsScene *scene, QWidget *parent)
         : QGraphicsView(scene, parent), totalScaleFactor(1)
     {
         viewport()->setAttribute(Qt::WA_AcceptTouchEvents);
         setDragMode(ScrollHandDrag);
     }

     bool GraphicsView::viewportEvent(QEvent *event)
     {
         switch (event->type()) {
         case QEvent::TouchBegin:
         case QEvent::TouchUpdate:
         case QEvent::TouchEnd:
         {
             QTouchEvent *touchEvent = static_cast<QTouchEvent *>(event);
             QList<QTouchEvent::TouchPoint> touchPoints = touchEvent->touchPoints();
             if (touchPoints.count() == 2) {
                 // determine scale factor
                 const QTouchEvent::TouchPoint &touchPoint0 = touchPoints.first();
                 const QTouchEvent::TouchPoint &touchPoint1 = touchPoints.last();
                 qreal currentScaleFactor =
                         QLineF(touchPoint0.pos(), touchPoint1.pos()).length()
                         / QLineF(touchPoint0.startPos(), touchPoint1.startPos()).length();
                 if (touchEvent->touchPointStates() & Qt::TouchPointReleased) {
                     // if one of the fingers is released, remember the current scale
                     // factor so that adding another finger later will continue zooming
                     // by adding new scale factor to the existing remembered value.
                     totalScaleFactor *= currentScaleFactor;
                     currentScaleFactor = 1;
                 }
                 setTransform(QTransform().scale(totalScaleFactor * currentScaleFactor,
                                                 totalScaleFactor * currentScaleFactor));
             }
             return true;
         }
         default:
             break;
         }
         return QGraphicsView::viewportEvent(event);
     }