基于QGraphicsView的图像显示控件，支持放大、缩小、鼠标拖动

原链接

前言

这是一个Qt平台的基于QGraphicsView类的图像显示控件，支持输入QPixmap、QImage、opencv的从cv::Mat类。
实现平台：Windows 10 x64 + Qt 6.2.3 + MSVC 2019 + opencv 4.5

先来看演示视频

控件类实现

ImageViewer.h文件

#ifndef IMAGEVIEWER_H
#define IMAGEVIEWER_H

#include <QObject>
#include <QGraphicsItem>
#include <QGraphicsView>
#include <QMouseEvent>
#include <QImage>
#include <QWheelEvent>
#include <QGraphicsScene>
#include "opencv2/opencv.hpp"

class ImageViewer : public QGraphicsView
{
    Q_OBJECT
public:
    explicit ImageViewer(QWidget *parent = nullptr);

signals:


public:
    void setQImage(QImage);
    void setMatImage(cv::Mat );
    void setPixmap(QPixmap);
    void resetImage();
    QImage getQImage();
    cv::Mat getMatImage();
    QPixmap getPixmap();

protected:
    virtual void wheelEvent(QWheelEvent *event) override;
    virtual void keyPressEvent(QKeyEvent *event) override;
    virtual void mousePressEvent(QMouseEvent *event) override;
    virtual void mouseMoveEvent(QMouseEvent *event) override;
    virtual void mouseReleaseEvent(QMouseEvent *event) override;
    void zoom(QPoint factor);
    void togglePan(bool pan, const QPoint &startPos = QPoint());
    void pan(const QPoint &panTo);
    void initShow();

private:
    QPixmap m_image;
    bool m_isPan;
    QPoint m_prevPan;
    QGraphicsScene *scene;

};

#endif // IMAGEVIEWER_H

ImageViewer.cpp 文件

#include "imageviewer.h"
#include <QScrollBar>

ImageViewer::ImageViewer(QWidget *parent)
    : QGraphicsView{parent},
    m_isPan(false),
    m_prevPan(0,0),
    scene(nullptr)
{
    scene = new QGraphicsScene(this);
    this->setScene(scene);

    setDragMode(QGraphicsView::DragMode::NoDrag);
    setInteractive(false);
    setEnabled(false);
}
QImage cvMatToQImage(cv::Mat &src)
{
    if(src.channels() == 1) { // if grayscale image
        return QImage((uchar*)src.data, src.cols, src.rows, static_cast<int>(src.step), QImage::Format_Grayscale8).copy();
    }
    if(src.channels() == 3) { // if 3 channel color image
        cv::Mat rgbMat;
        cv::cvtColor(src, rgbMat, cv::COLOR_BGR2RGB); // invert BGR to RGB
        return QImage((uchar*)rgbMat.data, src.cols, src.rows, static_cast<int>(src.step), QImage::Format_RGB888).copy();
    }
    return QImage();
}

//将QImage转化为Mat
cv::Mat qImageToCvMat( const QImage &inImage)
{
    switch (inImage.format())
    {
    case QImage::Format_RGB32:
    case QImage::Format_RGB888:
    {

        QImage   swapped = inImage;
        if ( inImage.format() == QImage::Format_RGB32 )
        {
            swapped = swapped.convertToFormat( QImage::Format_RGB888 );
        }
        cv::Mat matImg = cv::Mat(swapped.height(), swapped.width(),
                                  CV_8UC3,
                                  const_cast<uchar*>(swapped.bits()),
                                  static_cast<size_t>(swapped.bytesPerLine())
                                  );
        cv::cvtColor(matImg,matImg,cv::COLOR_RGB2BGR);
        return matImg.clone();
    }
    case QImage::Format_Indexed8:
    {
        cv::Mat  mat( inImage.height(), inImage.width(),
                      CV_8UC1,
                      const_cast<uchar*>(inImage.bits()),
                      static_cast<size_t>(inImage.bytesPerLine())
                      );
        return mat.clone();
    }
    default:
        break;
    }
    return cv::Mat();
}

void ImageViewer::setQImage(QImage image)
{   if(image.isNull())
        return;
    m_image = QPixmap::fromImage(image);
    initShow();
}
void ImageViewer::setMatImage(cv::Mat src)
{
    if(src.empty())
        return;
    m_image = QPixmap::fromImage(cvMatToQImage(src));
    initShow();
}
void ImageViewer::setPixmap(QPixmap pixmap)
{
    m_image = pixmap.copy();
    initShow();
}
void ImageViewer::resetImage()
{
    if(m_image.isNull())
        return;
    scene->clear();
    setEnabled(false);
}
QImage  ImageViewer::getQImage()
{
    return m_image.toImage();
}
cv::Mat ImageViewer::getMatImage()
{
    return qImageToCvMat(m_image.toImage());
}
QPixmap ImageViewer::getPixmap()
{
    return m_image;
}
void ImageViewer::initShow()
{
    setEnabled(true);
    setMouseTracking(true);
    scene->clear();
    scene->addPixmap(m_image);
    scene->update();
    this->resetTransform();
    this->setSceneRect(m_image.rect());
    this->fitInView(QRect(0, 0, m_image.width(), m_image.height()), Qt::KeepAspectRatio);
}
void ImageViewer::mousePressEvent(QMouseEvent *event)
{
    if(event->button() == Qt::LeftButton){
        togglePan(true, event->pos());
        event->accept();
        return;
    }
    event->ignore();
}

void ImageViewer::mouseMoveEvent(QMouseEvent *event)
{
    if(m_isPan) {
        pan(event->pos());
        event->accept();
        return;
    }
    event->ignore();
}


void ImageViewer::mouseReleaseEvent(QMouseEvent *event)
{
    if(event->button() == Qt::LeftButton){
        togglePan(false);
        event->accept();
        return;
    }
    event->ignore();
}

void ImageViewer::zoom(QPoint factor)
{
    QRectF FOV = this->mapToScene(this->rect()).boundingRect();
    QRectF FOVImage = QRectF(FOV.left(), FOV.top(), FOV.width(), FOV.height());
    float scaleX = static_cast<float>(m_image.width()) / FOVImage.width();
    float scaleY = static_cast<float>(m_image.height()) / FOVImage.height();
    float minScale = scaleX > scaleY ? scaleY : scaleX;
    float maxScale = scaleX > scaleY ? scaleX : scaleY;
    if ((factor.y() > 0 && minScale > 100) || (factor.y() < 0 && maxScale < 1 )) {
      return;
    }
    if(factor.y()>0)
        scale(1.2, 1.2);
    else
        scale(0.8, 0.8);
}
void ImageViewer::keyPressEvent(QKeyEvent *event)
{
    if(event->key() == Qt::Key_O) {
        this->resetTransform();
        this->setSceneRect(m_image.rect());
        this->fitInView(QRect(0, 0, m_image.width(), m_image.height()), Qt::KeepAspectRatio);
    }
}

void ImageViewer::pan(const QPoint &panTo)
{
    auto hBar = horizontalScrollBar();
    auto vBar = verticalScrollBar();
    auto delta = panTo - m_prevPan;
    m_prevPan = panTo;
    hBar->setValue(hBar->value() - delta.x());
    vBar->setValue(vBar->value() - delta.y());
}

void ImageViewer::wheelEvent(QWheelEvent *event)
{
    if(m_image.isNull())
        return;
    QPoint numDegrees = event->angleDelta() / 8;
    if (!numDegrees.isNull()) {
        QPoint numSteps = numDegrees / 15;
        zoom(numSteps);
    }
    event->accept();
}


void ImageViewer::togglePan(bool pan, const QPoint &startPos)
{
    if(pan){
        if(m_isPan) {
            return;
        }
        m_isPan = true;
        m_prevPan = startPos;
        setCursor(Qt::ClosedHandCursor);
    } else {
        if(!m_isPan) {
            return;
        }
        m_isPan = false;
        m_prevPan = QPoint(0,0);
        setCursor(Qt::ArrowCursor);
    }
}

控件类的使用

具体使用代码如下
1、初始化类对象，并加入界面布局中

	//初始化图片浏览控件，并添加到布局
  	m_view = new ImageViewer(this);
   	//在界面的一个布局中加入控件
   	ui->horizontalLayout_3->addWidget(m_view);

2、打开图像，并加载到控件中

QString filename = getFilePath(QDir::currentPath(),this);
    qDebug() << filename;
    if(filename == "")
        return;
    //读取为QPixmap
    QPixmap mapImg(filename);
    m_view->setPixmap(mapImg);

    //读取为QImage
//    QImage img(filename);
//    m_view->setQImage(img);

    //读取为cv::Mat
//    cv::Mat matImg = cv::imread(filename.toLocal8Bit().data(),cv::IMREAD_UNCHANGED);
//    m_view->setMatImage(matImg);

3、从控件中卸载图片