#include "widget.h"Widget::Widget():BigButton("放大",this),LittleButton("缩小",this),LiftButton("向左",this),RightButton("向右",this),UpButton("向上",this),DownButton("向下",this),Paint(10,10,810,810),Alloffset(0,0),label("100%",this)
{ratio=1.0;             //初始化图片缩放比例action= Widget::None;pixW =985;            //设置图片尺寸为985*740pixH=740;pix =new QPixmap;pix->load(":/pic/img.jpg");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()));label.move(840,200);resize(890,850);}bool Widget::event(QEvent * event)
{static bool press=false;static QPoint PreDot;if(event->type()== QEvent::MouseButtonPress ){QMouseEvent *mouse=dynamic_cast<QMouseEvent* >(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<QMouseEvent* >(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<QMouseEvent* >(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);int NowW=ratio *pixW;int NowH=ratio *pixH;if(action==Widget::Amplification)           //缩小
{ratio-=0.1*ratio;if(ratio<0.018)ratio =0.01;QString str;str.sprintf("%.0f%",ratio*100);label.setText(str) ;
}
else  if(action==Widget::Shrink)           //放大
{ratio+=0.1*ratio;if(ratio>4.5)ratio =5.000;QString str;str.sprintf("%.0f%",ratio*100);label.setText(str);
}
if(action==Widget::Amplification || action==Widget::Shrink)      //更新图片
{NowW =ratio *pixW;NowH =ratio *pixH;pix->load(":/pic/img.jpg");                 //重新装载,因为之前的图片已经被缩放过*pix=pix->scaled(NowW, NowH,Qt::KeepAspectRatio);action=Widget::None;}if(action==Widget::Move)                    //移动
{int offsetx=Alloffset.x()+offset.x();Alloffset.setX(offsetx);int offsety=Alloffset.y()+offset.y();Alloffset.setY(offsety);action=Widget::None;
}if(abs(Alloffset.x())>=(Paint.width()/2 + NowW/2 -10))    //限制X偏移值
{if(Alloffset.x()>0)Alloffset.setX(Paint.width()/2 + NowW/2 -10);elseAlloffset.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);elseAlloffset.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.drawRect(Paint.x()-1,Paint.y()-1,Paint.width()+1,Paint.height()+1); //画框painter.drawTiledPixmap(x+Paint.x(),y+Paint.y(),w,h,*pix,sx,sy);             //绘画图形
}void  Widget::onLittleClicked()
{action=Widget::Amplification;this->update();
}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::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();
}

文章来源：https://www.cnblogs.com/lifexy/p/9057046.html