Synchronizing mouse wheel and MarbleWidget (ZoomIn(), ZoomOut() ) - c++

Question

I use MarbleWidget with OpenStreetMap on Qt.
Wheel zoom shows blurry images on the map. Therefore, I want to synchronize the mouse wheel with ZoomIn() and ZoomOut() inorder user to get sharp images on the map.
I want to do something like this:
QObject::connect( MarbleWidget, SIGNAL(??????), this, SLOT(wheelEvent(wheelEvent)) );
void MainWindow::wheelEvent(QWheelEvent *event){
//....
}
Is there any signal or event that I can use from MarbleWidget for ??????? above line?
And, how can I disable the mouse zoom on the MarbleWidget?

Answer 1

You can make your own input handler and tell MarbleWidget to use it. This will allow you to intercept mouse wheel events in the way you are asking.
Create a custom input handler
MarbleWidget uses a default input handler. Inside of MarbleInputHandler.cpp there is a function eventFilter(QObject*, QEvent*) that handles (among other things) the QEvent::Wheel event. Derive from this class and override eventFilter:
class MyMarbleInputHandler : public MarbleWidgetDefaultInputHandler
{
Q_OBJECT
public:
explicit MyMarbleInputHandler(MarbleWidget* mw) :
MarbleWidgetDefaultInputHandler(mw) {}
virtual bool eventFilter(QObject *o, QEvent *e);
signals:
void wheelEvent(QWheelEvent *event);
};
Basically, you want to intercept QEvent::Wheel and emit your own signal. Anything you don't handle yourself should be passed along to the base class.
bool MyMarbleInputHandler::eventFilter(QObject *o, QEvent *e)
{
if (e->type() == QEvent::Wheel)
{
emit wheelEvent(static_cast<QWheelEvent*>(e));
return true;
}
return MarbleWidgetDefaultInputHandler::eventFilter(o, e);
}
Create a custom MarbleWidget
The constructor below shows how you can set the input handler defined above. You'll also have to wire the signal/slot.
class MyMarbleWidget : public MarbleWidget
{
Q_OBJECT
public:
explicit MyMarbleWidget()
{
MyMarbleInputHandler *myMarbleInputHandler = new MyMarbleInputHandler(this);
setInputHandler(myMarbleInputHandler);
connect(myMarbleInputHandler, SIGNAL(wheelEvent(QWheelEvent*)),
this, SLOT(handleWheelEvent(QWheelEvent*)));
}
public slots:
void handleWheelEvent(QWheelEvent *event)
{
if (event->delta() > 0) zoomIn();
else zoomOut();
}
};
handleWheelEvent() provides the code to zoom in/out. Not all scroll wheels work the same, so you'll have to figure out how much movement of the mouse wheel it will take to zoom in/out by one step. In this example, it zooms in/out one step based on each event, paying attention only to the sign of delta() and ignoring its magnitude.
You might also check out MarbleDefaultInputHandler::handleWheel() to see what's going on with the default behavior. They use interpolated/stretched bitmap images between vector layers to provide a smoother animation when zooming. Note that the plus+ and minus- keys on the keyboard will allow you to zoom to non-interpolated map levels, whereas the mouse wheel zooms using animated ("blurry") interpolated layers. This behavior is documented in a bug report.