qt graphicsscene line 子类

Posted 2023-02-14

【中文标题】qt graphicsscene line 子类

【英文标题】：qt graphicsscene line subclass

【发布时间】：2017-04-17 16:57:41

【问题描述】：

我从 GraphicsScene 类中添加了一个 Line 子类来绘制一条线。从 MainWindow 我调用该类中的 line 函数，没有错误，但没有绘制线。我知道这一定是缺乏我的 C++ 技能。但是搜索并没有帮助我解决这个问题。我想要的是制作不同的类来绘制不同的形状，而不是用所有代码污染 GraphicsScene，以保持事物有点结构化。但是我做错了什么？我在 github github.com/JackBerkhout/QT_Draw001 上发布了我的代码

line.h

#ifndef LINE_H
#define LINE_H

#include <QMainWindow>
#include <QObject>
#include <QDebug>
#include "graphicsscene.h"

class Line: public GraphicsScene

public:
    Line();
    void drawLine(int x1, int y1, int x2, int y2);
;

#endif // LINE_H

line.cpp

#include "line.h"

Line::Line():
    GraphicsScene()



void Line::drawLine(int x1, int y1, int x2, int y2)

    // Just draw something by clicking a button

    qDebug() << "line";                 // This debug message is shown

    QColor color;
    color.setRgb(128, 0, 255);
    QPen pen;
    pen.setColor(color);
    pen.setWidth(20);
    pen.setCapStyle(Qt::RoundCap);

    this->addLine(x1, y1, x2, y2, pen); // Didn't draw the line on the scene

图形场景.cpp

#ifndef GRAPHICSSCENE_H
#define GRAPHICSSCENE_H

#include <QGraphicsScene>
#include <QGraphicsSceneMouseEvent>
#include <QPointF>
#include <QList>

class GraphicsScene : public QGraphicsScene

    Q_OBJECT
public:
    explicit GraphicsScene(QObject *parent = 0);
    virtual void mouseDoubleClickEvent(QGraphicsSceneMouseEvent * mouseEvent);
    virtual void mouseMoveEvent(QGraphicsSceneMouseEvent * mouseEvent);
    virtual void mousePressEvent(QGraphicsSceneMouseEvent * mouseEvent);
    virtual void mouseReleaseEvent(QGraphicsSceneMouseEvent * mouseEvent);

    QPointF getMousePoint(void);
    int getMouseX(void);
    int getMouseY(void);
    int getNumber(void);
    void setNumber(int num);

    QPointF mousePoint;
    int MouseX, MouseY;
    int myNumber;

signals:
    void changedMousePosition(QPointF mousePoint);
    void changedNumber(int myNumber);

public slots:

private:
    QList <QPointF> mousePoints;

//    int Number;

;

#endif // GRAPHICSSCENE_H

图形场景.cpp

#include "mainwindow.h"
#include "graphicsscene.h"
#include <QDebug>

GraphicsScene::GraphicsScene(QObject *parent) :
    QGraphicsScene(parent)

    this->setBackgroundBrush(Qt::black);
    myNumber = 0;
//    this-> ->setMouseTracking(true);


void GraphicsScene::mouseDoubleClickEvent(QGraphicsSceneMouseEvent * mouseEvent)

//    mousePoint = mouseEvent->scenePos();
//    MouseX = mousePoint.x();
//    MouseY = mousePoint.y();
    qDebug() << Q_FUNC_INFO << mouseEvent->scenePos();
    QGraphicsScene::mouseDoubleClickEvent(mouseEvent);


void GraphicsScene::mouseMoveEvent(QGraphicsSceneMouseEvent * mouseEvent)

    mousePoint = mouseEvent->scenePos();
    MouseX = mouseEvent->scenePos().x();
    MouseY = mouseEvent->scenePos().y();

    emit changedMousePosition(mousePoint);

    QGraphicsScene::mouseMoveEvent(mouseEvent);


void GraphicsScene::mousePressEvent(QGraphicsSceneMouseEvent * mouseEvent)

    mousePoint = mouseEvent->scenePos();
    MouseX = mouseEvent->scenePos().x();
    MouseY = mouseEvent->scenePos().y();
    mousePoints.append(mouseEvent->scenePos());

    MainWindow *mainWindow = new MainWindow();
    mainWindow->Count++;

    if(mousePoints.size() == 2)
    
        myNumber++;

        emit changedNumber(myNumber);

        QColor color;
        color.setRgb(128, 0, 255);
        QPen pen;
        pen.setColor(color);
        pen.setWidth(20);
        pen.setCapStyle(Qt::RoundCap);
        this->addLine(mousePoints.at(0).x(), mousePoints.at(0).y(), mousePoints.at(1).x(), mousePoints.at(1).y(), pen);

        mousePoints.clear();
    

    QGraphicsScene::mousePressEvent(mouseEvent);


void GraphicsScene::mouseReleaseEvent(QGraphicsSceneMouseEvent * mouseEvent)

    mousePoint = mouseEvent->scenePos();
    MouseX = mouseEvent->scenePos().x();
    MouseY = mouseEvent->scenePos().y();
    QGraphicsScene::mouseReleaseEvent(mouseEvent);


QPointF GraphicsScene::getMousePoint(void)

    return mousePoint;


int GraphicsScene::getMouseX(void)

    MouseX = mousePoint.x();
    return mousePoint.x();


int GraphicsScene::getMouseY(void)

    MouseY = mousePoint.y();
    return mousePoint.y();


void GraphicsScene::setNumber(int num)

    myNumber = num;


int GraphicsScene::getNumber(void)

    return myNumber;

【问题讨论】：

当我想到它时，对不同的形状进行子类化可能没有意义。它使事情变得复杂。

【参考方案1】：

你太复杂了，除了我认为你不明白继承的目的是什么，你只需要在GraphicsScene中创建一个名为drawLine的函数，并在需要时使用它。

GraphicsScene.h

public:

    void drawLine(int x1, int y1, int x2, int y2);

GraphicsScene.cpp

void GraphicsScene::drawLine(int x1, int y1, int x2, int y2)

    QColor color;
    color.setRgb(128, 0, 255);
    QPen pen;
    pen.setColor(color);
    pen.setWidth(20);
    pen.setCapStyle(Qt::RoundCap);

    addLine(x1, y1, x2, y2, pen);

然后你在主窗口中调用：

void MainWindow::on_toolButtonDraw_clicked()

    scene->drawLine(300, 100, 500, 300);

当您创建 Line 对象时，您正在创建一个新场景，它将在该场景中绘制，因此您将看不到它。

【讨论】：

如果我想画橡皮筋线，我想我需要使用XOR，我找不到方法，我认为GraphicsScene 没有使用QPainter。有没有办法做到这一点？或者我可以制作一个单独的透明场景图层来绘制和擦除，而不破坏显示的内容吗？

我尝试将 QPainter 与 GraphicsScene 一起使用，但无法编译。错误：没有匹配函数调用‘QPainter::QPainter(GraphicsScene*)’ QPainterpainter(this); ^ void GraphicsScene::myLine(int x1, int y1, int x2, int y2) QPoint point1, point2; point1.setX(x1); point1.setY(y1); point2.setX(x2); point2.setY(y2); QPainter 画家（本）； Painter.setCompositionMode(QPainter::RasterOp_SourceXorDestination);画家.drawLine（point1，point2）；

什么是橡皮筋线？

我更新了我的 github 链接，现在包含它。当我开始画一条线时，从原点到鼠标位置绘制一条细虚线，并在单击第二个点之前随鼠标移动。当我用黑色绘制它们时，它会擦除​​已经绘制的线条。一些层或 XOR 操作在这里会派上用场，但我还不知道该怎么做。 github.com/JackBerkhout/QT_Draw001 在 line.cpp, setLineP2(int x, int y)

我将为这个问题开始一个新问题，因为它在这里是题外话。到目前为止非常感谢！