Объединение решения @veslam: s с кодом Smooth Zoom из QT Wiki ( https://wiki.qt.io/Smooth_Zoom_In_QGraphicsView ) работает очень хорошо:
Источник:
QGraphicsViewMap::QGraphicsViewMap(QWidget *parent) : QGraphicsView(parent)
{
setTransformationAnchor(QGraphicsView::NoAnchor);
setResizeAnchor(QGraphicsView::NoAnchor);
}
void QGraphicsViewMap::wheelEvent(QWheelEvent* event)
{
wheelEventMousePos = event->pos();
int numDegrees = event->delta() / 8;
int numSteps = numDegrees / 15; // see QWheelEvent documentation
_numScheduledScalings += numSteps;
if (_numScheduledScalings * numSteps < 0) // if user moved the wheel in another direction, we reset previously scheduled scalings
_numScheduledScalings = numSteps;
QTimeLine *anim = new QTimeLine(350, this);
anim->setUpdateInterval(20);
connect(anim, SIGNAL (valueChanged(qreal)), SLOT (scalingTime(qreal)));
connect(anim, SIGNAL (finished()), SLOT (animFinished()));
anim->start();
}
void QGraphicsViewMap::scalingTime(qreal x)
{
QPointF oldPos = mapToScene(wheelEventMousePos);
qreal factor = 1.0+ qreal(_numScheduledScalings) / 300.0;
scale(factor, factor);
QPointF newPos = mapToScene(wheelEventMousePos);
QPointF delta = newPos - oldPos;
this->translate(delta.x(), delta.y());
}
void QGraphicsViewMap::animFinished()
{
if (_numScheduledScalings > 0)
_numScheduledScalings--;
else
_numScheduledScalings++;
sender()->~QObject();
}
Заголовок:
class QGraphicsViewMap : public QGraphicsView
{
Q_OBJECT
private:
qreal _numScheduledScalings = 0;
QPoint wheelEventMousePos;
public:
explicit QGraphicsViewMap(QWidget *parent = 0);
signals:
public slots:
void wheelEvent(QWheelEvent* event);
void scalingTime(qreal x);
void animFinished();
};