15、Qt显示图片并支持缩放、移动等操作 |
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15、Qt显示图片并支持缩放、移动等操作
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一、新建项目
点击“New Project”，选择“Application”“Qt Widget Application”，点击“Choose”
更改项目名称和位置
选择编译器
默认
默认
右击项目名，选择“Add New”
选择“C++” -> "C++ Class"，点击“Choose”
更改名称和基类
默认
更改photolabel.h的代码 #ifndef PHOTOLABEL_H #define PHOTOLABEL_H #include #include #include class PhotoLabel : public QLabel { public: explicit PhotoLabel(QWidget *parent = nullptr); void setPhoto(QString); //设置图片 void clearShow(); //清空显示 protected: void contextMenuEvent(QContextMenuEvent *event) override; //右键菜单 void paintEvent(QPaintEvent *event); //QPaint画图 void wheelEvent(QWheelEvent *event) override; //鼠标滚轮滚动 void mousePressEvent(QMouseEvent *event) override; //鼠标摁下 void mouseMoveEvent(QMouseEvent *event) override; //鼠标松开 void mouseReleaseEvent(QMouseEvent *event) override; //鼠标发射事件 private slots: void initWidget(); //初始化 void onSelectImage(); //选择打开图片 void onZoomInImage(); //图片放大 void onZoomOutImage(); //图片缩小 void onPresetImage(); //图片还原 private: QImage m_image; //显示的图片 qreal m_zoomValue = 1.0; //鼠标缩放值 int m_xPtInterval = 0; //平移X轴的值 int m_yPtInterval = 0; //平移Y轴的值 QPoint m_oldPos; //旧的鼠标位置 bool m_pressed = false; //鼠标是否被摁压 QString m_localFileName; //文件名称 QMenu *m_menu; //右键菜单 }; #endif // PHOTOLABEL_H更改photolabel.cpp的代码 #include "photolabel.h" #include #include #include #include PhotoLabel::PhotoLabel(QWidget *parent):QLabel(parent) { initWidget(); } /** * @brief PhotoLabel::initWidget 初始化 */ void PhotoLabel::initWidget() { //初始化右键菜单 m_menu = new QMenu(this); QAction *loadImage = new QAction; loadImage->setText("选择图片"); connect(loadImage, &QAction::triggered, this, &PhotoLabel::onSelectImage); m_menu->addAction(loadImage); m_menu->addSeparator(); QAction *zoomInAction = new QAction; zoomInAction->setText("放大"); connect(zoomInAction, &QAction::triggered, this, &PhotoLabel::onZoomInImage); m_menu->addAction(zoomInAction); QAction *zoomOutAction = new QAction; zoomOutAction->setText("缩小"); connect(zoomOutAction, &QAction::triggered, this, &PhotoLabel::onZoomOutImage); m_menu->addAction(zoomOutAction); QAction *presetAction = new QAction; presetAction->setText("还原"); connect(presetAction, &QAction::triggered, this, &PhotoLabel::onPresetImage); m_menu->addAction(presetAction); m_menu->addSeparator(); QAction *clearAction = new QAction; clearAction->setText("清空"); connect(clearAction, &QAction::triggered, this, &PhotoLabel::clearShow); m_menu->addAction(clearAction); } /** * @brief PhotoLabel::setPhoto 设置要显示的图片 * @param path 图片路径 */ void PhotoLabel::setPhoto(QString path) { if(path.isEmpty()) { return; } m_zoomValue = 1.0; m_xPtInterval = 0; m_yPtInterval = 0; m_localFileName = path; m_image.load(m_localFileName); update(); } /** * @brief PhotoLabel::clearShow 清空 */ void PhotoLabel::clearShow() { m_localFileName = ""; m_image = QImage(); this->clear(); } /** * @brief PhotoLabel::paintEvent 绘图事件 * @param event */ void PhotoLabel::paintEvent(QPaintEvent *event) { if(m_image.isNull()) return QWidget::paintEvent(event); QPainter painter(this); // 根据窗口计算应该显示的图片的大小 int width = qMin(m_image.width(), this->width()); int height = int(width * 1.0 / (m_image.width() * 1.0 / m_image.height())); height = qMin(height, this->height()); width = int(height * 1.0 * (m_image.width() * 1.0 / m_image.height())); // 平移 painter.translate(this->width() / 2 + m_xPtInterval, this->height() / 2 + m_yPtInterval); // 缩放 painter.scale(m_zoomValue, m_zoomValue); // 绘制图像 QRect picRect(-width / 2, -height / 2, width, height); painter.drawImage(picRect, m_image); QWidget::paintEvent(event); } /** * @brief PhotoLabel::wheelEvent 滚轮滚动缩放图片 * @param event */ void PhotoLabel::wheelEvent(QWheelEvent *event) { int value = event->delta(); if (value > 0) //放大 onZoomInImage(); else //缩小 onZoomOutImage(); update(); } /** * @brief PhotoLabel::mousePressEvent 鼠标按下，为移动图片做准备 * @param event */ void PhotoLabel::mousePressEvent(QMouseEvent *event) { m_oldPos = event->pos(); m_pressed = true; this->setCursor(Qt::ClosedHandCursor); //设置鼠标样式 } /** * @brief PhotoLabel::mouseMoveEvent 鼠标按下后，再移动鼠标，图片随之移动 * @param event */ void PhotoLabel::mouseMoveEvent(QMouseEvent *event) { if (!m_pressed) return QWidget::mouseMoveEvent(event); QPoint pos = event->pos(); int xPtInterval = pos.x() - m_oldPos.x(); int yPtInterval = pos.y() - m_oldPos.y(); m_xPtInterval += xPtInterval; m_yPtInterval += yPtInterval; m_oldPos = pos; update(); } /** * @brief PhotoLabel::mouseReleaseEvent 鼠标抬起，图片移动结束 */ void PhotoLabel::mouseReleaseEvent(QMouseEvent */*event*/) { m_pressed = false; this->setCursor(Qt::ArrowCursor); //设置鼠标样式 } /** * @brief PhotoLabel::contextMenuEvent 右键显示菜单栏 * @param event */ void PhotoLabel::contextMenuEvent(QContextMenuEvent *event) { QPoint pos = event->pos(); pos = this->mapToGlobal(pos); m_menu->exec(pos); } /** * @brief PhotoLabel::onSelectImage 选择图片 */ void PhotoLabel::onSelectImage() { QString path = QFileDialog::getOpenFileName(this, "选择 要显示的图片", "./", tr("Images (*.png *.jpg *.jpeg)")); if (path.isEmpty()) return; setPhoto(path); } /** * @brief PhotoLabel::onZoomInImage 图片放大 */ void PhotoLabel::onZoomInImage() { m_zoomValue += 0.05; update(); } /** * @brief PhotoLabel::onZoomOutImage 图片缩小 */ void PhotoLabel::onZoomOutImage() { m_zoomValue -= 0.05; if (m_zoomValue |
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