20.QT-Qpixmap实现图片鼠标缩放,鼠标拖动示例(详解)-白红宇的个人博客

20.QT-Qpixmap实现图片鼠标缩放,鼠标拖动示例(详解)

发布日期：2021-05-09 04:36:07 浏览次数：16 分类：博客文章

本文共 7602 字，大约阅读时间需要 25 分钟。

通过 QPainter 绘画实现,以本地图片985*740为例

如下图所示:

效果如下所示:

实现原理

主要通过以下函数实现:

void QPainter::drawTiledPixmap ( int x, int y, int w int h const QPixmap & pixmap, int sx = 0, int sy = 0 );　　　　　　//平铺显示pixmap　　　　　　//x y w h :表示绘画区域　　　　　　//sx  sy  :表示Qpixmap绘画起始位置

只要算出x y w h sx sy就能实现超出窗口不显示的效果

举个例子,如下图所示,居中显示1200*1200时：

当图片左偏移600时,也就是offset=-600时,则只能在窗口上显示一半的图片：

2020-11-25更新

由于本笔记是当时才学QT时写的,所以图片都是指定的某资源,而不是通过QFileDialog来打开文件,如下图所示:

本用来记笔记给自己看的,结果很多参考代码的人,直接复制代码,然后忘记改图片资源,效果展示不出来,以为是代码问题.

所以更新,界面如下所示,添加了两个button,还原100%显示大小、打开文件按钮:

代码实现（直接复制粘贴到widget界面类即可）

widget.h:

#ifndef WIDGET_H#define WIDGET_H#include 
    
     #include 
     
      #include 
      
       #include 
       
        #include 
        
         #include 
         
          #include 
          
           #include 
           
            class Widget : public QWidget{ Q_OBJECTprivate : QPixmap pix; QPixmap crtPix; int action; //动作(放大,缩小,移动...) int pixW; //图片宽 int pixH; //图片高 QRect Paint; //绘画区域 QImage image; //打开的图片 float ratio; //缩放比例 QPoint offset; //一次的图片偏移值 QPoint Alloffset; //总偏移 QLabel label; QPushButton BigButton; QPushButton LittleButton; QPushButton LiftButton; QPushButton RightButton; QPushButton UpButton; QPushButton DownButton; QPushButton ResetButton; QPushButton OpenButton; void AddComboItem(QComboBox* cmbo); bool event(QEvent * event); void wheelEvent(QWheelEvent* e); //鼠标滑轮事件private slots: void onUpClicked(); void onDownClicked(); void onResetClicked(); void OnLiftClicked(); void OnRightClicked(); void onLittleClicked(); void onBigClicked(); void onOpenClicked(); void paintEvent(QPaintEvent *event);public: explicit Widget(); enum Type { None = 0, Amplification , Shrink, Lift, Right, Up, Down, Move, Reset };};#endif // WIDGET_H

widget.cpp:

#include "widget.h"Widget::Widget():    Paint(10,10,810,810),    BigButton("放大",this),    LittleButton("缩小",this),    LiftButton("向左",this),    RightButton("向右",this),    UpButton("向上",this),    DownButton("向下",this),    ResetButton("还原",this),    OpenButton("打开文件",this),    Alloffset(0,0),    label("100%",this){    ratio= 1.0;             //初始化图片缩放比例    action = Widget::None;    BigButton.setGeometry(822,10,60,25);    connect(&BigButton,SIGNAL(clicked()),this,SLOT(onBigClicked()));    LittleButton.setGeometry(822,40,60,25);    connect(&LittleButton,SIGNAL(clicked()),this,SLOT(onLittleClicked()));    LiftButton.setGeometry(822,70,60,25);    connect(&LiftButton,SIGNAL(clicked()),this,SLOT(OnLiftClicked()));    RightButton.setGeometry(822,100,60,25);    connect(&RightButton,SIGNAL(clicked()),this,SLOT(OnRightClicked()));    UpButton.setGeometry(822,130,60,25);    connect(&UpButton,SIGNAL(clicked()),this,SLOT(onUpClicked()));    DownButton.setGeometry(822,160,60,25);    connect(&DownButton,SIGNAL(clicked()),this,SLOT(onDownClicked()));    ResetButton.setGeometry(822,190,60,25);    connect(&ResetButton,SIGNAL(clicked()),this,SLOT(onResetClicked()));    OpenButton.setGeometry(822,220,60,25);    connect(&OpenButton,SIGNAL(clicked()),this,SLOT(onOpenClicked()));    label.move(840,260);    resize(890,850);    this->setWindowTitle("图片浏览器(请打开文件)");}bool Widget::event(QEvent * event){    static bool press=false;    static QPoint PreDot;    if(event->type() == QEvent::MouseButtonPress )    {           QMouseEvent *mouse = dynamic_cast
    
     (event);           //判断鼠标是否是左键按下,且鼠标位置是否在绘画区域           if(mouse->button()==Qt::LeftButton &&Paint.contains(mouse->pos()))           {               press=true;               QApplication::setOverrideCursor(Qt::OpenHandCursor); //设置鼠标样式               PreDot = mouse->pos();           }    }    else if(event->type() == QEvent::MouseButtonRelease)    {        QMouseEvent *mouse = dynamic_cast
     
      (event);        //判断鼠标是否是左键释放,且之前是在绘画区域        if(mouse->button()==Qt::LeftButton && press )        {            QApplication::setOverrideCursor(Qt::ArrowCursor); //改回鼠标样式            press=false;        }    }     if(event->type() == QEvent::MouseMove)              //移动图片     {          if(press)         {            QMouseEvent *mouse = dynamic_cast
      
       (event);            offset.setX(mouse->x() - PreDot.x());            offset.setY(mouse->y() - PreDot.y());            PreDot = mouse->pos();            action = Widget::Move;            this->update();         }     }    return QWidget::event(event);}void Widget::wheelEvent(QWheelEvent* event)     //鼠标滑轮事件{ if (event->delta()>0) {      //上滑,缩小    action=Widget::Shrink;    this->update(); } else {                    //下滑,放大     action=Widget::Amplification;     this->update(); } event->accept();}void Widget::paintEvent(QPaintEvent *event){    QPainter painter(this);    painter.setRenderHints(QPainter::SmoothPixmapTransform|QPainter::Antialiasing|QPainter::TextAntialiasing);    painter.drawRect(Paint.x()-1,Paint.y()-1,Paint.width()+1,Paint.height()+1); //画框    if(image.isNull())    {     return;    }    int NowW = ratio *pixW;    int NowH = ratio *pixH;    if(action==Widget::Shrink)           //缩小    {          ratio-=0.05*ratio;        if(ratio<0.018)          ratio = 0.01;        /*显示比例*/        QString str;        str.sprintf("%.0f%",ratio*100);        label.setText(str) ;        qDebug()<<"缩小:"<
       
        4.5)         ratio = 5.000;        /*显示比例*/        QString str;        str.sprintf("%.0f%",ratio*100);        label.setText(str);        qDebug()<<"放大:"<
        
         =(Paint.width()/2 + NowW/2 -10))    //限制X偏移值    {        if(Alloffset.x()>0)            Alloffset.setX(Paint.width()/2 + NowW/2 -10);        else         Alloffset.setX(-Paint.width()/2 + -NowW/2 +10);    }    if(abs(Alloffset.y())>=(Paint.height()/2 + NowH/2 -10))    //限制Y偏移值    {        if(Alloffset.y()>0)            Alloffset.setY(Paint.height()/2 + NowH/2 -10);        else         Alloffset.setY(-Paint.height()/2 + -NowH/2 +10);    }    int x = Paint.width()/2 + Alloffset.x() -NowW/2;    if(x<0)        x=0;    int y = Paint.height()/2 + Alloffset.y() -NowH/2;    if(y<0)        y=0;    int  sx = NowW/2 - Paint.width()/2 - Alloffset.x();    if(sx<0)        sx=0;    int  sy = NowH/2 - Paint.height()/2 - Alloffset.y();    if(sy<0)        sy=0;    int w =(NowW - sx)>Paint.width()? Paint.width() : (NowW - sx);    if(w>(Paint.width()-x))        w = Paint.width()-x;    int h =(NowH - sy)>Paint.height()? Paint.height() : (NowH - sy);    if(h>(Paint.height()-y))        h = Paint.height()-y;    painter.drawTiledPixmap(x+Paint.x(),y+Paint.y(),w,h,crtPix,sx,sy);             //绘画图形}void  Widget::onLittleClicked(){  action=Widget::Amplification;  this->update();}void Widget::onOpenClicked(){    QString str = QFileDialog::getOpenFileName(this,                                 "open",                                 "D:",                                 "img (*.png *.jpg)");    if(!str.isNull())    {       image.load(str);       pix = pix.fromImage(image);       crtPix = pix;       pixW = image.width();            //图片宽       pixH = image.height();           //图片高       qDebug()<
         
          <
          
           <
           
            setWindowTitle("图片浏览器("+str+")"); onResetClicked(); }}void Widget::onBigClicked(){ action=Widget::Shrink; this->update();}void Widget::onUpClicked(){ action=Widget::Move; offset.setX(0); offset.setY(-20); this->update();}void Widget::onDownClicked(){ action=Widget::Move; offset.setX(0); offset.setY(20); this->update();}void Widget::onResetClicked(){ action=Widget::Reset; Alloffset.setX(0); Alloffset.setY(0); ratio = 1.000; label.setText("100%"); this->update();}void Widget::OnLiftClicked(){ action=Widget::Move; offset.setX(-20); offset.setY(0); this->update();}void Widget::OnRightClicked(){ action=Widget::Move; offset.setX(20) ; offset.setY(0) ; this->update();}

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