C++基于QWidget和QLabel实现图片缩放,拉伸与拖拽

最近做ffmpeg视频拉流解码，涉及到截图功能的图片显示操作，特此做记录。

头文件

#ifndef QPICTURESHOT_H
#define QPICTURESHOT_H
 
#include <QWidget>
#include <QLabel>
 
class QPictureShot : public QWidget
{
    Q_OBJECT
 
public:
    explicit QPictureShot(QWidget *parent = nullptr);
 
    ~QPictureShot();
 
 
    //接收一张图片文件路径
    void inputPicFile(QString sFile);
 
    //设置定时消失
    void setAutoDismiss(int nShowSeconds);
 
protected:
 
private:
    //初始化窗体部件
    void InitLayout();
 
    void wheelEvent(QWheelEvent * event) override;
    void resizeEvent(QResizeEvent* event) override ;
    void mousePressEvent(QMouseEvent *event) override;
    void mouseMoveEvent(QMouseEvent *event) override;
    void mouseReleaseEvent(QMouseEvent *event) override;
 
    QLabel *m_pPicLabel;    //图片
    QImage m_image;
    QRect m_initRect;
 
    double opacityValue;//窗体初始化透明度
    float ratio = 1.0f;
    bool m_bLeftPress;//左键按下
    float m_difX;
http://www.devze.com    float m_difY;
 
 
};
 
#endif // QPICTURESHOT_H

cpp文件：

#include "qpictureshot.h"
#include <QApplication>
#include <QDesktopWidget>
#include <QPainter>
#include <QTimer>
#include <QMouseEvent>
#include <QDebug>
 
 
#ifdef WIN32
#pragma execution_character_set("utf-8")
#endif
 
QPictureShot::QPictureShot(QWidget *parent):
    QWidget(parent),
    m_pPicLabel(new QLabel(this)),
    opacityValue(1.0)
{
    setWindowFlags(Qt::Window  |Qt::WindowTitleHint | Qt::CustomizeWindowHint | Qt::WindowCloseButtonHint | Qt::WindowMaximizeButtonHint);
    setWindowTitle("图片");
    this->setAttribute(Qt::WA_TranslucentBackground);
    InitLayout();
}
 
 
QPictureShot::~QPictureShot()
{
 
}
 
 
//接收一张图片文件路径
void QPictureShot::inputPicFile(QString sFile)
{
    int nPos = sFile.lastIndexOf("/");
    QString sText = sFile.right(sFile.length() - nPos - 1);
    setWindowTitle(sText);
 
    m_image = QImage(sFile);
    if (m_image.isNull())
    {
        m_pPicLabel->setStyleSheet("font-size:18pt;color:white;");
        m_pPicLabel->setAlignment(Qt::AlignCenter);
        m_pPicLabel->setText("文件不存在");
    }
    else
    {
        QPixmap pix = QPixmap::fromImage(m_image);
        pix编程客栈 = pix.scaled(m_pPicLabel->width(), m_pPicLabel->height(), Qt::IgnoreASPectRatio, Qt::SmoothTransformation);
 
        m_pPicLabel->setScaledContents(true);
        m_pPicLabel->setPixmap(pix);
    }
 
}
 
/php/设置定时消失
void QPictureShot::setAutoDismiss(int nShowSeconds)
{
    QTimer *mtimer = new QTimer(this);//隐藏的定时器
    mtimer->setTimerType(Qt::PreciseTimer);
    connect(mtimer,&QTimer::timeout,this,[=](){
        if(opacityValue<=0){ this->close(); }
        opacityValue = opacityValue-0.1;
        this->setWindowOpacity(opacityValue);    //设置窗口透明度
        });
 
 
    QTimer *mShowtimer = new QTimer(this);//显示时间的定时器
    mShowtimer->setTimerType(Qt::PreciseTimer);// 修改定时器对象的精度
    connect(mShowtimer,&QTimer::timeout,this,[=](){
        mtimer->start(100);//执行延时自动关闭
    js    });
    mShowtimer->start(nShowSeconds);
}
//初始化窗体部件
void QPictureShot::InitLayout()
{
    //设置部件大小
    QDesktopWidget* desktop = QApplication::desktop(); // =qApp->desktop();也可以
    this->resize(desktop->width() * 0.8, desktop->height() * 0.8);
    m_pPicLabel->setGeometry(0, 0, desktop->width() * 0.8, desktop->height() * 0.8);
    m_pPicLabel->setCursor(QCursor(Qt::PointingHandCursor));
    m_initRect = this->rect();
 
}
 
void QPictureShot::wheelEvent(QWheelEvent * event)
{ 
    if (m_image.isNull()) return;
 
    QPoint numDegrees = event->angleDelta() / 120;
    float ratio_temp =  (1 + numDegrees.y() / 20.0);
    ratio *= ratio_temp;//在当前的比例基础上乘以
    if (ratio > 3 || ratio < 0.05) return;
 
    int w = ratio_temp*m_pPicLabel->width(); //显示宽度
    int h = ratio_temp*m_pPicLabel->height(); //显示高度
 
    QPoint mousePos = event->pos();
    QPoint picPos = m_pPicLabel->pos();
    int pageWidth = mousePos.x() - picPos.x();
    int pageHeight = mousePos.y() - picPos.y();
 
 
    QPixmap pix = QPixmap::fromImage(m_image);
    pix = pix.scaled(w, h, Qt::IgnoreAspectRatio, Qt::SmoothTransformation); //图像缩放到指定高度和宽度，保持长宽比例
 
    m_pPicLabel->setScaledContents(true);
    m_pPicLabel->setPixmap(pix);
 
    int nMoveX =  pageWidth * (numDegrees.y() / 20.0);
    int nMoveY =  pageHeight * (numDegrees.y() / 20.0);
    m_pPicLabel->setGeometry(m_pPicLabel->pos().x() - nMoveX, m_pPicLabel->pos().y() - nMoveY, w, h);
 
 
}
 
void QPictureShot::mousePressEvent(QMouseEvent *event)
{
    if(event->buttons() & Qt::LeftButton)
    {
        m_bLeftPress = true;
        m_difX = event->pos().x() - m_pPicLabel->x();
        m_difY = event->pos().y() - m_pPicLabel->y();
    }
}
void QPictureShot::mouseMoveEvent(QMouseEvent *event)
{
    if (m_bLeftPress)
    {
        int x = event->pos().x() - m_difX;
        int y = event->pos().y() - m_difY;
        m_pPicLabel->move(x, y);
    }
}
void QPictureShot::mouseReleaseEvent(QMouseEvent *event)
{
    Q_UNUSED(event);
    m_bLeftPress = false;
}
 
 
 
void QPictureShot::resizeEvent(QResizeEvent* evepythonnt) {
    // 在此处添加对窗口拉伸事件的处理逻辑
    // 输出新的大小信息
    qDebug("New size: %dx%d", width(), height());
 
    float x_ratio = width() * 1.0 / m_initRect.width();
    float y_ratio = height() * 1.0 / m_initRect.height();
 
    m_pPicLabel->setGeometry(m_pPicLabel->x() * x_ratio, m_pPicLabel->y() * y_ratio,  m_pPicLabel->width() * x_ratio, m_pPicLabel->height() * y_ratio);
    if (!m_image.isNull())
    { 
        QPixmap pix = QPixmap::fromImage(m_image);
        pix = pix.scaled(this->width(), this->height(), Qt::IgnoreAspectRatio, Qt::SmoothTransformation);
 
        m_pPicLabel->setScaledContents(true);
        m_pPicLabel->setPixmap(pix);
    }
 
    m_initRect = this->rect();
    // 调用基类的resizeEvent()函数，确保默认行为也得到执行
    QWidget::resizeEvent(event);
}

测试入口代码

QPictureShot *pic = new QPictureShot(this);
    pic->inputPicFile(":/bg.png");
    pic->show();

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