- Qt 6.11
- Qt Charts
- Qt Charts Examples
- Zoom Line Example
- Qt Charts | Commercial or GPLv3

# Zoom Line Example

The example shows how to create your own custom zooming effect.

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.

#### Running the Example

You can run the example from:

- Qt Creator

  Open the Welcome mode and select the example from Examples. For more information, see Qt Creator: Tutorial: Build and run.

- Qt Extension for Visual Studio Code

  Run the Qt: Open Qt examples command from the Command Palette, and select the example from the list. For more information, see Qt Extension for Visual Studio Code: Tutorial: Build and run.

#### Customizing Zooming Effects

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

         auto series = new QLineSeries;
         for (int i = 0; i < 500; i++) {
             QPointF p((qreal) i, qSin(M_PI / 50 * i) * 100);
             p.ry() += QRandomGenerator::global()->bounded(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)) {
             auto pan = static_cast<QPanGesture *>(gesture);
             QChart::scroll(-(pan->delta().x()), pan->delta().y());
         }

         if (QGesture *gesture = event->gesture(Qt::PinchGesture)) {
             auto 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.

Example project @ code.qt.io