src/graphicsview.cpp


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#include "graphicsview.h"

// qt
#include <QWheelEvent>

GraphicsView::GraphicsView(QWidget* parent)
    : QGraphicsView{parent}
{
    init();
}

GraphicsView::GraphicsView(QGraphicsScene* scene, QWidget* parent)
    : QGraphicsView{scene, parent}
{
    init();
}

void GraphicsView::wheelEvent(QWheelEvent* event)
{
    setTransformationAnchor(GraphicsView::AnchorUnderMouse);

    QPoint pixels = event->pixelDelta();
    QPoint degrees = event->angleDelta();
    const auto oldScenePos = event->scenePosition();
    const auto oldMapped = mapToScene(event->position().toPoint());

    if (pixels.isNull() && degrees.isNull())
        return;

    const double scaleMultiplier{1.1};
    const auto steps = double(pixels.isNull() ? degrees.y() : pixels.y());
    auto actualScale = std::abs(steps) * scaleMultiplier /
                       double(QWheelEvent::DefaultDeltasPerStep);

    if (steps < 0)
        actualScale = 1 / actualScale;

    scale(actualScale, actualScale);

    event->accept();
}

void GraphicsView::init()
{
    setDragMode(QGraphicsView::ScrollHandDrag);
    setRenderHint(QPainter::Antialiasing, true);
}