pan when mousewheel pressed in Qt C++ - c++

Question

I've got an application which handles zooming in/out using the mouse wheel with this event in Qt Creator.
cpp
void QNodeView::wheelEvent(QWheelEvent* event) {
setTransformationAnchor(QGraphicsView::AnchorUnderMouse);
// Scale the view / do the zoom
double scaleFactor = 1.15;
if(event->delta() > 0) {
// Zoom in
scale(scaleFactor, scaleFactor);
} else {
// Zooming out
scale(1.0 / scaleFactor, 1.0 / scaleFactor);
}
}
This is in the header file
h
protected:
//Take over the interaction
virtual void wheelEvent(QWheelEvent* event);
How can I add the ability to pan with the middle mouse button being pressed the user dragging the cursor?
I can post the project code if necessary just ask.
Thanks
Project files link (Qt Creator project)
https://www.dropbox.com/s/gbt4qqtdedltxek/QNodesEditor-master_01.zip?dl=0

Answer 1

At first, introduce some new member variables into your viewer class:
class QNodeView : public QGraphicsView
{
// ...
private:
int m_originalX = 0;
int m_originalY = 0;
bool m_moving = false;
};
Then reimplement mousePressEvent(), mouseMoveEvent(), and mouseReleaseEvent().
void QNodeView::mousePressEvent(QMouseEvent* event)
{
if (event->button() == Qt::MiddleButton)
{
// store original position
m_originalX = event->x();
m_originalY = event->y();
// set the "moving" state
m_moving = true;
}
}
void QNodeView::mouseMoveEvent(QMouseEvent* event)
{
if (m_moving)
{
// panning operates in the scene coordinates using x,y
QPointF oldp = mapToScene(m_originalX, m_originalY);
QPointF newp = mapToScene(event->pos());
QPointF translation = newp - oldp;
translate(translation.x(), translation.y());
m_originalX = event->x();
m_originalY = event->y();
}
}
void QNodeView::mouseReleaseEvent(QMouseEvent* event)
{
if (event->button() == Qt::MiddleButton)
{
m_moving = false;
}
}