qlabel实现图像以鼠标为中心进行缩放和拖动

#ifndef MYLABEL_H
#define MYLABEL_H

#include <QObject>
#include <QLabel>
#include <QMouseEvent>
#include <QWheelEvent>
#include <QPainter>
#include <QDebug>

class MyLabel:public QLabel
{
public:
    MyLabel(QWidget *parent=nullptr);

protected:
    void paintEvent(QPaintEvent *) override;
    void mouseMoveEvent(QMouseEvent *ev) override;
    void mousePressEvent(QMouseEvent *ev) override;
    void mouseReleaseEvent(QMouseEvent *ev) override;
    void wheelEvent(QWheelEvent *event) override;
    void resizeEvent(QResizeEvent *event) override;
    void changeWheelValue(QPoint event,int value);
private:
    double m_scaleValue;      // 图片缩放倍数
    QPointF m_drawPoint;      // 绘图起点
    QPointF m_mousePoint;     // 鼠标当前位置点
    QRect m_rectPixmap;       // 被绘图片的矩形范围
    bool m_isMousePress;      // 鼠标是否按下

    const double SCALE_MAX_VALUE=10.0;//最大放大到原来的10倍
    const double SCALE_MIN_VALUE=0.5;//最小缩小到原来的0.5倍
};

#endif // MYLABEL_H

#include "mylabel.h"

MyLabel::MyLabel(QWidget *parent):QLabel(parent)
  ,m_scaleValue(1.0)
  ,m_mousePoint(0,0)
  ,m_drawPoint(0,0)
  ,m_rectPixmap(0,0,0,0)
  ,m_isMousePress(0)
{

}

void MyLabel::paintEvent(QPaintEvent *)
{
    QPainter painter(this);
    double width=this->width()*m_scaleValue;
    double height=this->height()*m_scaleValue;
    QPixmap scalePixmap=this->pixmap()->scaled(width,height,Qt::IgnoreAspectRatio, Qt::SmoothTransformation); // 饱满缩放
    m_rectPixmap=QRect(m_drawPoint.x(),m_drawPoint.y(),width,height);  // 图片区域
    painter.drawPixmap(m_rectPixmap,scalePixmap);
}

void MyLabel::mouseMoveEvent(QMouseEvent *event)
{
    if(m_isMousePress)
    {
        int x=event->pos().x()-m_mousePoint.x();
        int y=event->pos().y()-m_mousePoint.y();
        m_mousePoint=event->pos();
        m_drawPoint=QPointF(m_drawPoint.x()+x,m_drawPoint.y()+y);
        update();
    }
}

void MyLabel::mousePressEvent(QMouseEvent *event)
{
    if(event->button()==Qt::LeftButton)
    {
        m_isMousePress=true;
        m_mousePoint=event->pos();
    }
}

void MyLabel::mouseReleaseEvent(QMouseEvent *event)
{
    if(event->button() == Qt::RightButton)
    {
        m_drawPoint=QPointF(0,0);
        m_scaleValue=1.0;
        update();
    }
    if(event->button() == Qt::LeftButton) m_isMousePress=false;
}

void MyLabel::wheelEvent(QWheelEvent *event)
{
    changeWheelValue(event->pos(),event->delta());
    event->accept();
}

void MyLabel::resizeEvent(QResizeEvent *event)
{
    m_drawPoint=QPointF(0,0);
    m_scaleValue=1.0;
    update();
}

void MyLabel::changeWheelValue(QPoint event, int numSteps)
{
    double oldScale = m_scaleValue;
    if(numSteps>0)
    {
        m_scaleValue*=1.1;
    }
    else
    {
        m_scaleValue*=0.9;
    }
    if(m_scaleValue>(SCALE_MAX_VALUE))
    {
        m_scaleValue=SCALE_MAX_VALUE;
    }
    if(m_scaleValue<(SCALE_MIN_VALUE))
    {
        m_scaleValue=SCALE_MIN_VALUE;
    }

    if(m_rectPixmap.contains(event))
    {
        double x=m_drawPoint.x()-(event.x()-m_drawPoint.x())/m_rectPixmap.width()*(this->width()*(m_scaleValue-oldScale));
        double y=m_drawPoint.y()-(event.y()-m_drawPoint.y())/m_rectPixmap.height()*(this->height()*(m_scaleValue-oldScale));
        m_drawPoint=QPointF(x,y);
    }
    else
    {
        double x=m_drawPoint.x()-(this->width()*(m_scaleValue-oldScale))/2;
        double y=m_drawPoint.y()-(this->height()*(m_scaleValue-oldScale))/2;
        m_drawPoint=QPointF(x,y);
    }
    update();
}