Qt（十二）Graphics View 绘图架构（一）

一、Graphics View绘图架构

• QPainter不能实现图件的选择、编辑、拖放、修改等功能。
• QGraphicScene (场景) :可以管理多个图形项
• QGraphicsltem (图形项) : 也就是图元，支持鼠标事件响应。比如:矩形的图形项
• QGraphicsView (视图) :关联场景可以让场景中的所有图形项可视化
  视图坐标、场景坐标、图形项坐标、坐标 映射

QGraphicsView是Qt的图形视图组件，在U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

二、简单示例

创建项目UI设计

拖拽部件布局之后，新建类MyGraphicView 添加至本项目

将继承的基类修改为：QGraphicsView，将部件的基类提升至刚创建的类。

提升完成

详情代码

mygraphicview.h

#ifndef MYGRAPHICVIEW_H
#define MYGRAPHICVIEW_H

#include <QObject>
#include <QWidget>
#include <QPoint>
#include <QGraphicsView>
#include <QMouseEvent>

class MyGraphicView : public QGraphicsView
{
    
    
    Q_OBJECT
public:
    explicit MyGraphicView(QWidget *parent = nullptr);

protected:
    void mousePressEvent(QMouseEvent *event) override;
    void mouseMoveEvent(QMouseEvent *event) override;

signals:
    void mouseMovePoint(QPoint point);
    void mouseClick(QPoint point);

};

#endif // MYGRAPHICVIEW_H

mygraphicview.cpp

#include "mygraphicview.h"

MyGraphicView::MyGraphicView(QWidget *parent) : QGraphicsView(parent)
{
    
    

}

void MyGraphicView::mousePressEvent(QMouseEvent *event)
{
    
    
    if(event->button() == Qt::LeftButton){
    
    
        QPoint point = event->pos();          //view坐标
        emit mouseClick(std::move(point));
    }
    QGraphicsView::mousePressEvent(event);
}

void MyGraphicView::mouseMoveEvent(QMouseEvent *event)
{
    
    
    QPoint point = event->pos();
    emit mouseMovePoint(point);
    QGraphicsView::mouseMoveEvent(event);
}

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QLabel>
#include <QRectF>
#include <QGraphicsRectItem>
#include <QGraphicsEllipseItem>
#include <QPen>
#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();

protected:
    void resizeEvent(QResizeEvent *event) override;

private slots:
    void on_mouseMovePoint(QPoint point);
    void on_mouseClick(QPoint point);

private:
    Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"

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);

    QGraphicsEllipseItem *item2 = new QGraphicsEllipseItem(-100,-50,200,100);
    item2->setFlags(QGraphicsItem::ItemIsFocusable
                    |QGraphicsItem::ItemIsSelectable
                    |QGraphicsItem::ItemIsMovable);

    item2->setBrush(QBrush(Qt::blue));
    Scene->addItem(item2);


    QGraphicsEllipseItem *item3 = new QGraphicsEllipseItem(-50,-50,100,100);
    item3->setFlags(QGraphicsItem::ItemIsFocusable
                    |QGraphicsItem::ItemIsSelectable
                    |QGraphicsItem::ItemIsMovable);
    item3->setPos(rect.right(),rect.bottom());
    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->setMinimumWidth(150);
    ui->statusbar->addWidget(labViewCord);

    labSceneCord = new QLabel("Scene坐标：");
    labSceneCord->setMinimumWidth(150);
    ui->statusbar->addWidget(labSceneCord);

    labItemCord = new QLabel("Item坐标：");
    labItemCord->setMinimumWidth(150);
    ui->statusbar->addWidget(labItemCord);

    //设置光标-->光标跟踪
    ui->graphicsView->setCursor(Qt::CrossCursor);
    ui->graphicsView->setMouseTracking(true);
    connect(ui->graphicsView,SIGNAL(mouseMovePoint(QPoint)),this,SLOT(on_mouseMovePoint(QPoint)));
    connect(ui->graphicsView,SIGNAL(mouseClick(QPoint)),this,SLOT(on_mouseClick(QPoint)));
    initGraphics();
    ui->graphicsView->setCursor(Qt::CrossCursor);
}

MainWindow::~MainWindow()
{
    
    
    delete ui;
}

void MainWindow::resizeEvent(QResizeEvent *event)
{
    
    
    Q_UNUSED(event);
    ui->label_viewSize->setText(QString::asprintf(
                           "Graphics view坐标，左上角总是(0，0)，width=%d \t height=%d",
                           ui->graphicsView->width(),
                           ui->graphicsView->height()));

    QRectF rect = ui->graphicsView->sceneRect();
    ui->label_SceneRect->setText(QString::asprintf(
                             "Graphicsview::sceneRect=(x,y,w,h)=%.0f,%.0f,%.0f,%.0f",
                             rect.x(),rect.y(),rect.width(),rect.height()));
}


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_mouseClick(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(point);
        labItemCord->setText(QString::asprintf("Item坐标：%.0f,%.0f,",
                                               pointItem.x(),pointItem.y()));

    }
}

效果演示