Qt_图像放大缩小拖动 图片缩小放大平移

例程为qt5图片放大缩小平移，可直接运行，采用传递给子线程显示的方式

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关键代码：

void ImageShow::contextMenuEvent(QContextMenuEvent *event)

{

    QPoint pos = event->pos();

    pos = this->mapToGlobal(pos);

    QMenu *menu = new QMenu(this);

    QAction *zoomInAction = new QAction(tr("Zoom In"));

    QObject::connect(zoomInAction, &QAction::triggered, this, &ImageShow::onZoomInImage);

    menu->addAction(zoomInAction);

    QAction *zoomOutAction = new QAction(tr("Zoom Out"));

    QObject::connect(zoomOutAction, &QAction::triggered, this, &ImageShow::onZoomOutImage);

    menu->addAction(zoomOutAction);

    QAction *presetAction = new QAction(tr("Preset"));

    QObject::connect(presetAction, &QAction::triggered, this, &ImageShow::onPresetImage);

    menu->addAction(presetAction);

    menu->exec(pos);

}

void ImageShow::paintEvent(QPaintEvent *event)

{    

    QStyleOption opt;

    opt.init(this);

    QPainter painter(this);

    style()->drawPrimitive(QStyle::PE_Widget, &opt, &painter, this);

    if (m_Image.isNull())

        return QWidget::paintEvent(event);    

    int width = qMin(m_Image.width(), this->width());

    int height = width * 1.0 / (m_Image.width() * 1.0 / m_Image.height());

    height = qMin(height, this->height());

    width = height * 1.0 * (m_Image.width() * 1.0 / m_Image.height());    

    painter.translate(this->width() / 2 + m_XPtInterval, this->height() / 2 + m_YPtInterval);    

    painter.scale(m_ZoomValue, m_ZoomValue);    

    QRect picRect(-width / 2, -height / 2, width, height);

    painter.drawImage(picRect, m_Image);

}