Marble/MarbleSignalsSlots

Editing Projects/Marble/MarbleCPlusPlus

Basic interaction with MarbleWidget

Tutorial Series	Marble C++ Tutorial
Previous	Tutorial 2 - Changing basic map properties
What's Next	Tutorial 4 - GeoPainter: Painting onto the map
Further Reading	n/a

Creating a window with controls

We'd like to add other widgets to our Marble window: A zoom slider and a label that shows the current mouse position in geodetic coordinates: longitude and latitude.

In order to achieve this we need to create a vertical layout. Once done we add the slider and the label that we created to the layout. Also we zoom the globe to the slider's default value using the MarbleWidget::zoomView(int) method.

We want to center our globe onto South America. So we create a new GeoDataCoordinates object that takes the longitude and the latitude as a parameter and we call MarbleWidget::centerOn.

As you might have realized already GeoDataCoordinates is the geodetic "sister" of QPoint. They share a very similar API. Additionally GeoDataCoordinates features a nice set of string conversion methods (GeoDataCoordinates::fromString(), GeoDataCoordinates::lonToString() and GeoDataCoordinates::latToString() ). They are used in various places inside Marble such as the signal MarbleWidget::mouseMoveGeoPosition( const QString& ) .

Finally we connect the signals and slots that MarbleWidget offers to the signals and slots of the slider and the label:

include <QtGui/QApplication>

include <QtGui/QLayout>
include <QtGui/QSlider>
include <QtGui/QLabel>

include <marble/MarbleWidget.h>

using namespace Marble;
int main(int argc, char** argv)
{

   QApplication app(argc,argv);
   QWidget *window = new QWidget;

   // Create a Marble QWidget without a parent
   MarbleWidget *mapWidget = new MarbleWidget();

   // Load the Plain map
   mapWidget->setMapThemeId("earth/plain/plain.dgml");

   // Hide the FloatItems: OverviewMap, ScaleBar and Compass
   mapWidget->setShowOverviewMap(false);
   mapWidget->setShowScaleBar(false);
   mapWidget->setShowCompass(false);

   // Set the map quality to gain speed
   mapWidget->setMapQuality( NormalQuality, Still );
   mapWidget->setMapQuality( LowQuality, Animation );
   
   // Create a horizontal zoom slider and set the default zoom
   QSlider * zoomSlider = new QSlider(Qt::Horizontal);
   zoomSlider->setMinimum( 1000 );
   zoomSlider->setMaximum( 2400 );
   
   mapWidget->zoomView( zoomSlider->value() );

   // Create a label to show the geodetic position
   QLabel * positionLabel = new QLabel();
   positionLabel->setSizePolicy( QSizePolicy::Preferred, QSizePolicy::Fixed );

   // Add all widgets to the vertical layout.
   QVBoxLayout *layout = new QVBoxLayout;
   layout->addWidget(mapWidget);
   layout->addWidget(zoomSlider);
   layout->addWidget(positionLabel);

   // Center the map onto a given position
   GeoDataCoordinates home(-60.0, -10.0, 0.0, GeoDataCoordinates::Degree);
   mapWidget->centerOn(home);
   
   // Connect the map widget to the position label.
   QObject::connect( mapWidget, SIGNAL( mouseMoveGeoPosition( QString ) ),
                     positionLabel, SLOT( setText( QString ) ) );

   // Connect the zoom slider to the map widget and vice versa.
   QObject::connect( zoomSlider, SIGNAL( valueChanged(int) ),
                     mapWidget, SLOT( zoomView(int) ) );
   QObject::connect( mapWidget, SIGNAL( zoomChanged(int) ),
                     zoomSlider, SLOT( setValue(int) ) );

   window->setLayout(layout);
   window->resize( 400, 300 );

   window->show();

   return app.exec();

}

Save the code above as marble_control.cpp and compile it:

g++ -I /usr/include/qt4/ -o marble_control marble_control.cpp -lmarblewidget -lQtGui

If things go fine, execute ./marble_control and you end up with a map application that displays our globe with a zoom slider below: