Qt 5.7 | Qt Charts | Zoom Line Example

Qt 5.7.1 Reference Documentation

# Zoom Line Example

The example shows how to create your own custom zooming effect with QRubberBand by using a mouse and how to use touch gestures for paning and zooming.

Let's first create a line series with some example data.

          QLineSeries *series = new QLineSeries();
          for (int i = 0; i < 500; i++) {
              QPointF p((qreal) i, qSin(M_PI / 50 * i) * 100);
              p.ry() += qrand() % 20;
              *series << p;
          }

Then we create a custom chart view by deriving from QChartView:

      class ChartView : public QChartView

We override mouse and key event handling

      protected:
          bool viewportEvent(QEvent *event);
          void mousePressEvent(QMouseEvent *event);
          void mouseMoveEvent(QMouseEvent *event);
          void mouseReleaseEvent(QMouseEvent *event);
          void keyPressEvent(QKeyEvent *event);

Then we implement a custom logic for mouse and key events. For example pressing the '+' key will zoom in and pressing the '-' key will zoom out.

      void ChartView::keyPressEvent(QKeyEvent *event)
      {
          switch (event->key()) {
          case Qt::Key_Plus:
              chart()->zoomIn();
              break;
          case Qt::Key_Minus:
              chart()->zoomOut();
              break;

We also create our own QChart:

      class Chart : public QChart

Where we can handle the gestures:

      bool Chart::sceneEvent(QEvent *event)
      {
          if (event->type() == QEvent::Gesture)
              return gestureEvent(static_cast<QGestureEvent *>(event));
          return QChart::event(event);
      }

      bool Chart::gestureEvent(QGestureEvent *event)
      {
          if (QGesture *gesture = event->gesture(Qt::PanGesture)) {
              QPanGesture *pan = static_cast<QPanGesture *>(gesture);
              QChart::scroll(-(pan->delta().x()), pan->delta().y());
          }

          if (QGesture *gesture = event->gesture(Qt::PinchGesture)) {
              QPinchGesture *pinch = static_cast<QPinchGesture *>(gesture);
              if (pinch->changeFlags() & QPinchGesture::ScaleFactorChanged)
                  QChart::zoom(pinch->scaleFactor());
          }

          return true;
      }

Note that you will need to call grabGesture() to both QMainWindow and QChart.

Files:

- zoomlinechart/chart.cpp
- zoomlinechart/chart.h
- zoomlinechart/chartview.cpp
- zoomlinechart/chartview.h
- zoomlinechart/main.cpp
- zoomlinechart/zoomlinechart.pro