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

To run the example from Qt Creator, open the Welcome mode and select the example from Examples. For more information, visit Building and Running an Example.

Customizing Zooming Effects

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() += 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)) {
        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:

Voted #1 for:

  • Easiest to learn
  • Most time saving
  • Best support

Develop Cross-Platform Apps and Games 50% Faster!

  • Voted the best supported, most time-saving and easiest to learn cross-platform development tool
  • Based on the Qt framework, with native performance and appearance on all platforms including iOS and Android
  • Offers a variety of plugins to monetize, analyze and engage users
FREE!
create apps
create games
cross platform
native performance
3rd party services
game network
multiplayer
level editor
easiest to learn
biggest time saving
best support