QGraphicsView的使用，view坐标，scene坐标，item坐标

Graphics View绘图构架

QGraphicsScene（场景）：可以管理多个图形项
QGraphicsItem（图形项）：也就是图元，支持鼠标事件响应。
QGraphicsView（视图）：关联场景可以让场景中的所有图形项可视化

QGraphicsView是QT的图形视图组件，在UI设计器的Display Widgets分组

QGraphicsView没有与mouseMoveEvent()相关的信号，需要继承自定义一个派生类

代码演示

工程文件不需要添加模块

注意事项是，graphics需要派生一个类才能用事件等相关信息

所以要新建一个派生类：

mygraphicsview.h

#ifndef MYGRAPHICSVIEW_H
#define MYGRAPHICSVIEW_H
 
#include <QObject>
#include <QGraphicsView>
 
class mygraphicsview : public QGraphicsView
{
    Q_OBJECT
public:
    explicit mygraphicsview(QWidget *parent = nullptr);
protected:
    void mousePressEvent(QMouseEvent *event);
    void mouseMoveEvent(QMouseEvent *event);
signals:
    void mouseMovePoint(QPoint point);
    void mouseClicked(QPoint point);
 
};
 
#endif // MYGRAPHICSVIEW_H

mygraphicsview.cpp

#include "mygraphicsview.h"
 
#include <QMouseEvent>
 
mygraphicsview::mygraphicsview(QWidget *parent) : QGraphicsView(parent)
{
 
}
 
void mygraphicsview::mousePressEvent(QMouseEvent *event)
{
    if(event->button()==Qt::LeftButton)
    {
        QPoint point = event->pos();//view坐标
        emit mouseClicked(point);
    }
    QGraphicsView::mousePressEvent(event);
}
 
void mygraphicsview::mouseMoveEvent(QMouseEvent *event)
{
    QPoint point = event->pos();
    emit mouseMovePoint(point);
    QGraphicsView::mouseMoveEvent(event);
}

派生类的事件通过信号的方式发送出去，其他地方connect连接信号读取数据。

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
 
#include <QLabel>
#include <QMainWindow>
#include <QGraphicsScene>
 
QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE
 
class MainWindow : public QMainWindow
{
    Q_OBJECT
 
private:
    QLabel *labViewCord;
    QLabel *labSceneCord;
    QLabel *labItemCord;
    QGraphicsScene *scene;
 
    void initGraphics();
public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();
 
private:
    Ui::MainWindow *ui;
 
private slots:
    void on_mouseMovePoint(QPoint point);
    void on_mouseClicked(QPoint point);
 
protected:
    void resizeEvent(QResizeEvent *event);
};
#endif // MAINWINDOW_H

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
 
#include "mygraphicsview.h"
 
#include <QGraphicsRectItem>
 
void MainWindow::initGraphics()
{
    QRectF rect(-200,-100,400,200);
    scene = new QGraphicsScene(rect);
    ui->graphicsView->setScene(scene);
    QGraphicsRectItem *item = new QGraphicsRectItem(rect);
    item->setFlags(QGraphicsItem::ItemIsFocusable |
                   QGraphicsItem::ItemIsSelectable);
    QPen pen;
    pen.setWidth(2);
    item->setPen(pen);
    scene->addItem(item);
 
    //蓝色椭圆
    QGraphicsEllipseItem *item2 = new QGraphicsEllipseItem(-100,-50,200,100);
    item2->setPos(0,0);
    item2->setFlags(QGraphicsItem::ItemIsFocusable |
                    QGraphicsItem::ItemIsSelectable |
                    QGraphicsItem::ItemIsMovable);
    item2->setBrush(QBrush(Qt::blue));
    scene->addItem(item2);
    //红色小圆
    QGraphicsEllipseItem *item3 = new QGraphicsEllipseItem(-50,-50,100,100);
    item3->setPos(rect.right(),rect.bottom());
    item3->setFlags(QGraphicsItem::ItemIsFocusable |
                    QGraphicsItem::ItemIsSelectable |
                    QGraphicsItem::ItemIsMovable);
    item3->setBrush(QBrush(Qt::red));
    scene->addItem(item3);
}
 
MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    labViewCord = new QLabel("View坐标：");
    labViewCord->setMidLineWidth(150);
    ui->statusbar->addWidget(labViewCord);
    labSceneCord = new QLabel("Scene坐标：");
    labSceneCord->setMidLineWidth(150);
    ui->statusbar->addWidget(labSceneCord);
    labItemCord = new QLabel("Item坐标：");
    labItemCord->setMidLineWidth(150);
    ui->statusbar->addWidget(labItemCord);
 
    ui->graphicsView->setCursor(Qt::CrossCursor);//光标
    ui->graphicsView->setMouseTracking(true);//跟随鼠标
 
    connect(ui->graphicsView,&mygraphicsview::mouseMovePoint,
            this,&MainWindow::on_mouseMovePoint);
    connect(ui->graphicsView,&mygraphicsview::mouseClicked,
            this,&MainWindow::on_mouseClicked);
 
    initGraphics();
}
 
MainWindow::~MainWindow()
{
    delete ui;
}
 
void MainWindow::on_mouseMovePoint(QPoint point)
{
    labViewCord->setText(QString::asprintf("View坐标：%d,%d",
                                           point.x(),point.y()));
    QPointF pointScene = ui->graphicsView->mapToScene(point);
    labSceneCord->setText(QString::asprintf("Scene坐标：%.0f,%.0f",
                                           pointScene.x(),pointScene.y()));
}
 
void MainWindow::on_mouseClicked(QPoint point)
{
    QPointF pointScene = ui->graphicsView->mapToScene(point);
    QGraphicsItem *item = NULL;
    item = scene->itemAt(pointScene,ui->graphicsView->transform());
    if(item!=NULL)
    {
        QPointF pointItem = item->mapFromScene(pointScene);
        labItemCord->setText(QString::asprintf("Item坐标%.0f,%.0f",
                                     pointItem.x(),pointItem.y()));
    }
}
 
void MainWindow::resizeEvent(QResizeEvent *event)
{
    Q_UNUSED(event)
    ui->label->setText(QString::asprintf("Graphics View坐标"
                                         "宽=%d,高=%d",
                                         ui->graphicsView->width(),
                                         ui->graphicsView->height()));
    QRectF rect = ui->graphicsView->sceneRect();
    ui->label_2->setText(QString::asprintf("QGraphicsView::sceneRect="
                                           "(L,T,W,H)=%.0f,%.0f,%.0f,%.0f",
                                           rect.left(),
                                           rect.top(),
                                           rect.width(),
                                           rect.height()));
}

ui部分要注意，需要吧graphics的窗口提升关联到派生类，不要用他的默认类。