Qt QGraphics类应用——地图缩放选点

功能：

　　1、地图缩放

　　2、显示鼠标点经纬度

需求：

　　1、一张地图

　　2、地图左上角经纬度和地图右下角经纬度

成品：

代码：

mapwidget.h

#ifndef MAPWIDGET_H
#define MAPWIDGET_H

#include <QGraphicsView>
#include <QLabel>
#include <QMouseEvent>

class MapWidget : public QGraphicsView
{
    Q_OBJECT
public:
    MapWidget();

    void readMap();
    QPointF mapToMap(QPointF point);//用于场景坐标与地图坐标转换

protected:
    void drawBackground(QPainter *painter, const QRectF &rect);
    void mouseMoveEvent(QMouseEvent *event);//拖动
    void wheelEvent(QWheelEvent *event);    //缩放

private:
    QPixmap map;
    qreal   zoom;
    QLabel  *sceneCoord,*viewCoord,*mapCoord;
    double  x1,x2,y1,y2;
    int     scaleValue;
};

#endif // MAPWIDGET_H

mapwidget.cpp

#include "mapwidget.h"
#include <QFile>
#include <QDebug>
#include <qmath.h>
#include <QTextStream>
#include <QGraphicsScene>

#define ZOOM_IN_TIMES -5
#define ZOOM_OUT_TIMES 5
MapWidget::MapWidget()
{
    readMap();

    scaleValue = 0;
    int width  = map.width();
    int height = map.height();
    QGraphicsScene *scene = new QGraphicsScene(this);
    scene->setSceneRect( -width/2,-height/2,width,height );//中点和范围
    setScene(scene);
    setCacheMode(CacheBackground);//缓存背景

    QLabel *scenelabel = new QLabel(tr("GraphicsScene:"),this);
    QLabel *viewlabel  = new QLabel(tr("GraphicsView: "),this);
    QLabel *maplabel   = new QLabel(tr("Map:          "),this);

    sceneCoord = new QLabel(this);
    viewCoord  = new QLabel(this);
    mapCoord   = new QLabel(this);

    scenelabel->setGeometry(1,1,110,20);
    viewlabel->setGeometry(1,21,110,20);
    maplabel->setGeometry(1,41,110,20);
    sceneCoord->setGeometry(111,1,200,20);
    viewCoord->setGeometry(111,21,200,20);
    mapCoord->setGeometry(111,41,200,20);



}


void MapWidget::readMap()
{
    QString mapName;
    QFile mapFile(":/file/maps.txt");
    int ok = mapFile.open(QIODevice::ReadOnly | QIODevice::Text);
    qDebug()<<"ok="<<ok;
    if(ok)
    {
        QTextStream in(&mapFile);
        if(!in.atEnd())
        {
            in>>mapName;
            in>>x1>>y1>>x2>>y2;
        }
    }
    mapFile.close();
    map.load(":/image/China.jpg");
    qDebug()<<"mapName="<<mapName<<" x1="<<x1<<" y1="<<y1<<" x2="<<x2<<" y2="<<y2;
}

QPointF MapWidget::mapToMap(QPointF point)//场景坐标到地图坐标
{
    QPointF lonlat;
    qreal w = sceneRect().width();
    qreal h = sceneRect().height();

    qreal lon = x1+( (w/2+point.x())*qAbs(x1-x2)/w );
    qreal lat = y1-( (h/2+point.y())*qAbs(y1-y2)/h );

    lonlat.setX(lon);
    lonlat.setY(lat);
    return lonlat;
}

void MapWidget::drawBackground(QPainter *painter, const QRectF &rect)
{
    painter->drawPixmap( (int)sceneRect().left(),(int)sceneRect().top(),map );
}

void MapWidget::wheelEvent(QWheelEvent *event)
{
    qreal s=0;
    bool in = true;
    bool out = true;


    if(event->delta() >= 0)//delta返回滑动的距离
    {
        scaleValue += 1;
    }
    if(event->delta() < 0)//delta返回滑动的距离
    {
        scaleValue -= 1;
    }

    if( scaleValue < ZOOM_IN_TIMES )
    {
        scaleValue = ZOOM_IN_TIMES;
        in = false;
        return;
    }else if( scaleValue > ZOOM_OUT_TIMES )
    {
        scaleValue = ZOOM_OUT_TIMES;
        out = false;
        return;
    }


    if(in)
    {
        s = qPow(1.01,event->delta()/10);
    }
    if(out)
    {
        s = qPow(1/1.01,-event->delta()/10);
    }
    qDebug()<<"scaleValue="<<scaleValue;
    scale(s,s);
}

void MapWidget::mouseMoveEvent(QMouseEvent *event)
{
    //1.而由event->globalPos()获取的鼠标位置是鼠标偏离电脑屏幕左上角
    //（x=0,y=0）的位置；
    //2.由pos()获取的位置是主窗口（widget窗口）左上角（边框的左上角，外左上
    //角）相对于电脑屏幕的左上角的（x=0,y=0）偏移位置
    //视图坐标
    QPoint viewPoint = event->pos();
    viewCoord->setText( QString::number(viewPoint.x())+","+
                        QString::number(viewPoint.y()) );
    //场景坐标
    QPointF scenePoint = mapToScene(viewPoint);
    sceneCoord->setText( QString::number(scenePoint.x())+","+
                        QString::number(scenePoint.y()) );
    //地图坐标
    QPointF mapPoint = mapToMap(scenePoint);
    mapCoord->setText( QString::number(mapPoint.x(),10,7)+","+
                        QString::number(mapPoint.y(),10,7) );


}

main.cpp

#include "mapwidget.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MapWidget map;
    map.show();
    
    return a.exec();
}

map.txt

:/image/China.jpg 114.4665527 35.96022297 119.9597168 31.3911575