20.QT-Qpixmap实现图片鼠标缩放,鼠标拖动示例(详解)
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 <QWidget> #include <QtGui> #include <QLabel> #include <QPushButton> #include <QComboBox> #include <QApplication> #include <QFileDialog> #include <QImage> class Widget : public QWidget { Q_OBJECT private : 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<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); 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:"<<ratio; } else if(action==Widget::Amplification) //放大 { ratio+=0.05*ratio; if(ratio>4.5) ratio = 5.000; /*显示比例*/ QString str; str.sprintf("%.0f%",ratio*100); label.setText(str); qDebug()<<"放大:"<<ratio; } if(action==Widget::Amplification || action==Widget::Shrink || action==Widget::Reset) //更新图片 { NowW = ratio *pixW; NowH = ratio *pixH; crtPix= pix.scaled(NowW, NowH,Qt::KeepAspectRatio,Qt::SmoothTransformation); //重新装载 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.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()<<str<<pixW<<pixH; this->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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4.3 QT学习之路
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