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);      

}