graphics_view_zoom.cpp

#include "graphics_view_zoom.h"
#include <QApplication>
#include <QMouseEvent>
#include <QScrollBar>
#include <qmath.h>

Graphics_view_zoom::Graphics_view_zoom(QGraphicsView *view)
    : QObject(view)
    , _view(view)
{
    _view->viewport()->installEventFilter(this);
    _view->setMouseTracking(true);
    _modifiers = Qt::ControlModifier;
    _zoom_factor_base = 1.0015;
}

void Graphics_view_zoom::gentle_zoom(double factor)
{
    _view->scale(factor, factor);
    _view->centerOn(target_scene_pos);
    QPointF delta_viewport_pos = target_viewport_pos
                                 - QPointF(_view->viewport()->width() / 2.0,
                                           _view->viewport()->height() / 2.0);
    QPointF viewport_center = _view->mapFromScene(target_scene_pos) - delta_viewport_pos;
    _view->centerOn(_view->mapToScene(viewport_center.toPoint()));
    emit zoomed();
}

void Graphics_view_zoom::set_modifiers(Qt::KeyboardModifiers modifiers)
{
    _modifiers = modifiers;
}

void Graphics_view_zoom::set_zoom_factor_base(double value)
{
    _zoom_factor_base = value;
}

bool Graphics_view_zoom::eventFilter(QObject *object, QEvent *event)
{
    if (event->type() == QEvent::MouseMove) {
        QMouseEvent *mouse_event = static_cast<QMouseEvent *>(event);
        QPointF delta = target_viewport_pos - mouse_event->pos();
        if (qAbs(delta.x()) > 5 || qAbs(delta.y()) > 5) {
            target_viewport_pos = mouse_event->pos();
            target_scene_pos = _view->mapToScene(mouse_event->pos());
        }
    } else if (event->type() == QEvent::Wheel) {
        QWheelEvent *wheel_event = static_cast<QWheelEvent *>(event);
        if (QApplication::keyboardModifiers() == _modifiers) {
            if (wheel_event->angleDelta().y() != 0) {
                double angle = wheel_event->angleDelta().y();
                double factor = qPow(_zoom_factor_base, angle);
                gentle_zoom(factor);
                return true;
            }
        }
    }
    Q_UNUSED(object)
    return false;
}