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：
代码实现
widget.h:
#ifndef WIDGET_H#define WIDGET_H#include#include class Widget : public QWidget{ Q_OBJECTprivate : QPixmap *pix; 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 float ratio; //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; 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 OnLiftClicked(); void OnRightClicked(); void onLittleClicked(); void onBigClicked(); void paintEvent(QPaintEvent *event);public: explicit Widget(); enum Type { None = 0, Amplification , Shrink, Lift, Right, Up, Down, Move };};#endif // WIDGET_H
widget.cpp:
#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*740 pixH = 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 (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); 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; /*显示比例*/ 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; /*显示比例*/ 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); 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.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();}