Qt编写自定义控件：图片显示控件_qt 图片控件

#ifndef PICTUREVIEWINGCONTROL_H
#define PICTUREVIEWINGCONTROL_H
 
#include <QWidget>
 
class PictureViewingControl : public QWidget
{
    Q_OBJECT
 
public:
    PictureViewingControl(QWidget * parent = nullptr);
    ~PictureViewingControl();
    void setPixmap(const QString &imgFilePath);
 
private:
    void paintEvent(QPaintEvent *event)override;
    bool event(QEvent * event)override;
 
public:
    enum class ActionType
    {
        Amplification,//放大
        Shrink,//缩小
        Move,//移动
        None//不进行任何操作
    };
 
private:
    QPoint Alloffset;//总偏移
    QPoint offset;
    QRect paintRect;
    QRect drawRect;
    QPixmap img_src;//源图
    ActionType action;//操作
    double ratio;//缩放比例
};
 
#endif // PICTUREVIEWINGCONTROL_H

#include "pictureviewingcontrol.h"
#include <QWheelEvent>
#include <QPainter>
 
PictureViewingControl::PictureViewingControl(QWidget *parent):
    QWidget(parent)
{
    action = ActionType::None;//初始动作：什么都不做
    ratio = 1.0;
    Alloffset = QPoint(0,0);
}
 
PictureViewingControl::~PictureViewingControl()
{
}
 
bool PictureViewingControl::event(QEvent * event)
{
    static bool press = false;//是否按下了左键
    static QPoint PreDot;
    auto type = event->type();
 
    if(type == QEvent::MouseButtonPress )//鼠标按下事件
    {
        if(QMouseEvent *mouse = static_cast<QMouseEvent* >(event))
        {
            if(mouse->button() == Qt::LeftButton && drawRect.contains(mouse->pos()))
            {
               press = true;
               PreDot = mouse->pos();
               setCursor(QCursor(Qt::ClosedHandCursor));
            }
        }
    }
    else if(type == QEvent::MouseButtonRelease)//鼠标松开事件
    {
        if(QMouseEvent *mouse = static_cast<QMouseEvent* >(event))
        {
            if(mouse->button() == Qt::LeftButton && press)
            {
                press = false;
            }
            setCursor(QCursor(Qt::OpenHandCursor));
        }
    }
    else if(type == QEvent::MouseMove)//移动鼠标
    {
        if(press)
        {
            if(QMouseEvent *mouse = static_cast<QMouseEvent* >(event))
            {
                offset.setX(mouse->x() - PreDot.x());
                offset.setY(mouse->y() - PreDot.y());
                PreDot = mouse->pos();
                action = ActionType::Move;
                this->repaint();
            }
        }
    }
    else if(type == QEvent::Wheel)
    {
        if(QWheelEvent *mouse = static_cast<QWheelEvent* >(event))
        {
            if(mouse->angleDelta().y() < 0)
            {
                //下滑,缩小
                action = ActionType::Shrink;
                this->repaint();
                action = ActionType::None;
            }
            else
            {
                //上滑,放大
                action = ActionType::Amplification;
                this->repaint();
                action = ActionType::None;
            }
        }
    }
    return QWidget::event(event);
}
 
void PictureViewingControl::setPixmap(const QString & imgFilePath)
{
    img_src.load(imgFilePath);
    ratio = 0.2;
    Alloffset = QPoint(0,0);
    offset = QPoint(0,0);
    repaint();
}
 
void PictureViewingControl::paintEvent(QPaintEvent *event)
{
    if(img_src.isNull())
    {
        return;
    }
 
    auto rect = event->rect();
    paintRect = QRect(1, 1, rect.width() + 1, rect.height() + 1);
 
    QPainter painter(this);
    painter.setRenderHint(QPainter::Antialiasing);//开启抗锯齿
    int NowW = ratio * img_src.width();//缩放后的图片尺寸
    int NowH = ratio * img_src.height();
 
    if(action == ActionType::Shrink)//缩小
    {
        ratio -= 0.1 * ratio;
        if(ratio < 0.2)
        {
            ratio = 0.2;
        }
    }
 
    if(action == ActionType::Amplification)//放大
    {
        ratio += 0.1 * ratio;
        if(ratio > 2)
        {
            ratio = 2;
        }
    }
 
    auto temp_img = img_src.copy().scaled(NowW, NowH,Qt::KeepAspectRatio);
 
    if(action == ActionType::Move)//移动
    {
        Alloffset.setX(Alloffset.x() + offset.x());
        Alloffset.setY(Alloffset.y() + offset.y());
    }
 
    //限制偏移量 效果是图像超出边框太多则弹回来
    if(abs(Alloffset.x()) >= (paintRect.width()/2 + NowW/2 - 10))    //限制X偏移值
    {
        if(Alloffset.x() > 0)
        {
            Alloffset.setX(paintRect.width()/2 + NowW/2 - 100);//右
        }
        else
        {
            Alloffset.setX(-paintRect.width()/2 + -NowW/2 + 100);//左
        }
    }
    if(abs(Alloffset.y()) >= (paintRect.height()/2 + NowH/2 - 10))    //限制Y偏移值
    {
        if(Alloffset.y() > 0)
        {
            Alloffset.setY(paintRect.height()/2 + NowH/2 - 100);//下
        }
        else
        {
            Alloffset.setY(-paintRect.height()/2 + -NowH/2 + 100);//上
        }
    }
 
    int x = paintRect.width()/2 + Alloffset.x() - NowW/2;
    if(x < 0)
    {
        x = 0;
    }
 
    int y = paintRect.height()/2 + Alloffset.y() - NowH/2;
    if(y < 0)
    {
       y = 0;
    }
 
    int  sx = NowW/2 - paintRect.width()/2 - Alloffset.x();
    if(sx < 0)
    {
       sx = 0;
    }
 
    int  sy = NowH/2 - paintRect.height()/2 - Alloffset.y();
    if(sy < 0)
    {
        sy = 0;
    }
 
    int w = (NowW - sx) > paintRect.width() ? paintRect.width(): (NowW - sx);
    if(w > (paintRect.width() - x))
    {
        w = paintRect.width() - x;
    }
 
    int h = (NowH - sy) > paintRect.height() ? paintRect.height() : (NowH - sy);
    if(h > (paintRect.height() - y))
    {
        h = paintRect.height() - y;
    }
 
    drawRect = QRect(x + paintRect.x(), y + paintRect.y(), w, h);
    painter.drawTiledPixmap(drawRect,temp_img,QPoint(sx, sy));  //绘画图片
}

效果：

#include "pictureviewingcontrol.h"
#include <QApplication>
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    PictureViewingControl w;
    w.setPixmap(":/backgroundImage1.jpg");
    w.show();
    return a.exec();
}