graphicsview.cpp Example File | Qt Widgets 5.12.7

Qt 5.12 | Qt Widgets | Pinch Zoom Example | graphicsview.cpp Example File

Qt 5.12.7 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);
      }