使用Qimage来实现图片的放大和缩小

#ifndef MYLABEL_H
#define MYLABEL_H

#include <QObject>
#include <QLabel>
#include <QMutex>

class MyLabel : public QLabel
{
    
	//Q_OBJECT
public:
	explicit MyLabel(QWidget *parent = 0);
	void SetImage(QImage image);
	QImage GetImage();
	void clear();
protected:
	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 mouseDoubleClickEvent(QMouseEvent *event) override;    //双击，还原图像大小
	void mouseMoveEvent(QMouseEvent *event) override;           //鼠标松开
	void mouseReleaseEvent(QMouseEvent *event) override;        //鼠标发射事件

private:
	void OnZoomInImage();       //图片放大
	void OnZoomOutImage();      //图片缩小
	void OnPresetImage();       //图片还原

private:
	QMutex m_Mutex;
	QImage m_Image;           //显示的图片
	qreal ZoomValue = 1.0;  //鼠标缩放值
	int XPtInterval = 0;    //平移X轴的值
	int YPtInterval = 0;    //平移Y轴的值
	QPoint OldPos;          //旧的鼠标位置
	bool Pressed = false;   //鼠标是否被摁压
};

#endif // MYLABEL_H

#include "mylabel.h"
#include <QPainter>
#include <QDebug>
#include <QWheelEvent>
#include <QMenu>
#include <QFileDialog>

MyLabel::MyLabel(QWidget *parent) :QLabel(parent)
{
    

}

//QPainter画图
void MyLabel::paintEvent(QPaintEvent *event)
{
    
	QPainter painter(this);
	painter.setRenderHints(QPainter::Antialiasing | QPainter::SmoothPixmapTransform);
	// 根据窗口计算应该显示的图片的大小
	m_Mutex.lock();
	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());

	// 平移
	painter.translate(this->width() / 2 + XPtInterval, this->height() / 2 + YPtInterval);

	// 缩放
	painter.scale(ZoomValue, ZoomValue);
	
	// 绘制图像
	QRect picRect(-width / 2, -height / 2, width, height);
	painter.drawImage(picRect, m_Image);
	m_Mutex.unlock();
}

//鼠标滚轮滚动
void MyLabel::wheelEvent(QWheelEvent *event)
{
    
	int value = event->delta();
	if (value > 0)  //放大
		OnZoomInImage();
	else            //缩小
		OnZoomOutImage();

	update();
}

//鼠标摁下
void MyLabel::mousePressEvent(QMouseEvent *event)
{
    
	OldPos = event->pos();
	Pressed = true;
}

void MyLabel::mouseDoubleClickEvent(QMouseEvent *event)
{
    
	if (event->button() == Qt::LeftButton)
	{
    
		ZoomValue = 1.0;
		XPtInterval = 0;
		YPtInterval = 0;
		update();
	}
}
//鼠标松开
void MyLabel::mouseMoveEvent(QMouseEvent *event)
{
    
	if (!Pressed)
		return QWidget::mouseMoveEvent(event);

	this->setCursor(Qt::SizeAllCursor);
	QPoint pos = event->pos();
	int xPtInterval = pos.x() - OldPos.x();
	int yPtInterval = pos.y() - OldPos.y();

	XPtInterval += xPtInterval;
	YPtInterval += yPtInterval;

	OldPos = pos;
	update();
}
//鼠标发射事件
void MyLabel::mouseReleaseEvent(QMouseEvent *event)
{
    
	Pressed = false;
	setCursor(Qt::ArrowCursor);
}

//图片放大
void MyLabel::OnZoomInImage()
{
    
	ZoomValue += 1;
	if (ZoomValue > 35)
	{
    
		ZoomValue = 35;
	}
	update();
}

//图片缩小
void MyLabel::OnZoomOutImage()
{
    
	ZoomValue -= 1;
	if (ZoomValue <= 0)
	{
    
		ZoomValue = 0.5;
		return;
	}

	update();
}

//图片还原
void MyLabel::OnPresetImage()
{
    
	ZoomValue = 1.0;
	XPtInterval = 0;
	YPtInterval = 0;
	update();
}

void MyLabel::SetImage(QImage image)
{
    
    //this->setScaledContents(true);//设置label允许缩放属性
    //image.scaled(this->size(),Qt::KeepAspectRatio, Qt::SmoothTransformation);//把图片缩放到label窗口适应的大小
	m_Mutex.lock();
	m_Image = image.copy(0,0,image.width(),image.height());
	m_Mutex.unlock();
	update();
}

QImage MyLabel::GetImage()
{
    
	return m_Image;
}

void MyLabel::clear()
{
    
	m_Mutex.lock();
	QPixmap pixmap = QPixmap("");
	m_Image = pixmap.toImage();
	m_Mutex.unlock();
	update();
}