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问QGraphicsScene中的弧
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Stack Overflow用户

提问于 2014-11-13 04:48:41

回答 2查看 10.1K关注 0票数 2

我想在QGraphicsScene中实现弧。我希望在点击三点时，我的弧线应该被画出来，在点击三点时，画出第一个点是弧线的起点，第二个点是弧线上的任意点，第三个点是弧的终点。我曾试过研究drawArc函数，但却把它弄糊涂了。我无法动态地设置它们。请建议我怎么做。

我尝试将该解决方案添加到我的项目中，但得到了以下错误：

error: cannot allocate an object of abstract type 'arc'
                 arcItem = new arc(++id, startP, midP, endP);

你能帮我解决这个问题吗？我为我的项目提供了一部分代码。在按摩器事件中，我做了下面的事情。

cadgraphicsscene.cpp

    void CadGraphicsScene::mousePressEvent(QGraphicsSceneMouseEvent *mouseEvent)
    {
        // mousePressEvent in the graphicsScene
        if(mouseEvent->button() == Qt::LeftButton)
        {
            switch (entityMode)
            {

            case ArcMode:
                if (mFirstClick)
                {
                    startP = mouseEvent->scenePos();
                    mFirstClick = false;
                    mSecondClick = true;
                }

                else if (!mFirstClick && mSecondClick)
                {
                    midP = mouseEvent->scenePos();
                    mFirstClick = false;
                    mSecondClick = false;
                    mThirdClick = true;
                }

                else if (!mSecondClick && mThirdClick)
                {
                    endP = mouseEvent->scenePos();
                    mThirdClick = false;
                    mPaintFlag = true;
                }

                if (mPaintFlag)
                {
                    arcItem = new arc(++id, startP, midP, endP);
                    itemList.append(arcItem);
                    mUndoStack->push(new CadCommandAdd(this, arcItem));
                    setFlags();
                }
            }
        }
   }

arc.cpp

#include "arc.h"

arc::arc(int i, QPointF point1, QPointF point2, QPointF point3)
{
    // assigns id
    id = i;
    p1 = point1;
    p2 = point2;
    p3 = point3;

    lineBC(point2, point3);
    lineAC(point1, point3);
    lineBA(point2, point1);

    rad = qAbs(lineBC.length()/(2*qSin(qDegreesToRadians(lineAC.angleTo(lineBA)))));

    bisectorBC(lineBC.pointAt(0.5), lineBC.p2());
    bisectorBC.setAngle(lineBC.normalVector().angle());

    bisectorBA(lineBA.pointAt(0.5), lineBA.p2());
    bisectorBA.setAngle(lineBA.normalVector().angle());


    bisectorBA.intersect(bisectorBC, &center);

    ellipse = new QGraphicsEllipseItem(center.x() - rad, center.y() - rad, rad*2, rad*2);

    lineOA(center, point1);
    lineOC(center, point3);
}

arc::arc(int i, QLineF start, QLineF end)
{
    // assigns id
    id = i;

    lineOA.angle() = start;
    lineOC.angle() - lineOA.angle() = end;
}

int arc::type() const
{
    // Enable the use of qgraphicsitem_cast with arc item.
    return Type;
}

void arc::paint(QPainter *painter, const QStyleOptionGraphicsItem *option,
                QWidget *widget)
{
    QPen paintpen;
    painter->setRenderHint(QPainter::Antialiasing);
    paintpen.setWidth(1);

    if (isSelected())
    {
        // sets brush for end points
        painter->setBrush(Qt::SolidPattern);
        paintpen.setColor(Qt::red);
        painter->setPen(paintpen);

        paintpen.setStyle(Qt::DashLine);
        paintpen.setColor(Qt::black);
        painter->setPen(paintpen);
        painter->drawArc(ellipse->boundingRect(),lineOA.angle(),lineOC.angle() - lineOA.angle());
    }
    else
    {
        painter->setBrush(Qt::SolidPattern);
        paintpen.setColor(Qt::black);
        painter->setPen(paintpen);
        painter->drawArc(ellipse->boundingRect(),lineOA.angle(),lineOC.angle() - lineOA.angle());

    }
}

arc.h

include <QGraphicsItem>

#include "qmath.h"
class arc : public QObject, public QGraphicsItem
{
    Q_OBJECT
public:
    arc(int, QPointF, QPointF, QPointF);
    arc(int, QLineF, QLineF);


    virtual void paint(QPainter *painter, const QStyleOptionGraphicsItem *option,
                       QWidget *widget);
    enum { Type = UserType + 6 };
    int type() const;
    int id;

    QPointF startP, midP, endP, p1, p2, p3,center;
    QLineF lineBC;
    QLineF lineAC;
    QLineF lineBA;
    QLineF lineOA;
    QLineF lineOC;
    QLineF bisectorBC;
    QLineF bisectorBA;
    QGraphicsEllipseItem *ellipse;
    qreal rad;

private:
    QVector<QPointF> stuff;

};

#endif // ARC_H

请帮我解决这个错误。

c++

qgraphicsview

qgraphicsscene

回答 2

Stack Overflow用户

回答已采纳

发布于 2014-11-14 20:10:24

QGraphicsItem的一个子类，它取3个点，并将这三个点与一个圆弧相交。第二点总是在中间。(可选性和其他属性尚未完全实现或测试)。

注意: Qt包含更高级的子类QGraphicsItem示例，例如碰撞鼠标，以及40000个芯片示例。

http://qt-project.org/doc/qt-5/examples-graphicsview.html

另外，要启用来自QObject的QGraphicsItem信号、插槽和属性，您应该使用QGraphicsObject。

注意:添加到github 这里中。

arcgraphicsitem.h

#ifndef ARCGRAPHICSITEM_H
#define ARCGRAPHICSITEM_H

#include <QGraphicsItem>
#include <QLineF>
#include <QPointF>
#include <QPainter>
#include <QStyleOptionGraphicsItem>
#include <QWidget>

class ArcGraphicsItem : public QGraphicsItem
{

public:
    ArcGraphicsItem();
    ArcGraphicsItem(int i, QPointF point0, QPointF point1, QPointF point2);
    ~ArcGraphicsItem();

    QRectF boundingRect() const;
    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);

    int type() const { return Type;}
    int id() {return m_id;}

    QPainterPath shape() const;
protected:

private:
    void init();

    enum { Type = UserType + 6 };
    int m_id;

    QPointF startP, midP, endP, p1, p2, p3, center;
    QLineF lineBC;
    QLineF lineAC;
    QLineF lineBA;
    QLineF lineOA;
    QLineF lineOB;
    QLineF lineOC;
    QLineF bisectorBC;
    QLineF bisectorBA;
    qreal startAngle;
    qreal spanAngle;

    QRectF circle;
    QRectF boundingRectTemp;
    qreal rad;
};

#endif // ARCGRAPHICSITEM_H

arcgraphicsitem.cpp

#include "arcgraphicsitem.h"
#include "qmath.h"
#include <QPen>
#include <QDebug>
#include <QPainterPath>

ArcGraphicsItem::ArcGraphicsItem(int i,
                                 QPointF point1,
                                 QPointF point2,
                                 QPointF point3)
    : m_id(i), p1(point1), p2(point2), p3(point3)

{
    init();
}


ArcGraphicsItem::ArcGraphicsItem()
{
    p1 = QPointF(0,0);
    p2 = QPointF(0,1);
    p3 = QPointF(1,1);
    m_id = -1;
    init();
}

ArcGraphicsItem::~ArcGraphicsItem()
{

}

void ArcGraphicsItem::init()
{
    lineBC = QLineF(p2, p3);
    lineAC = QLineF(p1, p3);
    lineBA = QLineF(p2, p1);

    rad = qAbs(lineBC.length()/(2*qSin(qDegreesToRadians(lineAC.angleTo(lineBA)))));

    bisectorBC = QLineF(lineBC.pointAt(0.5), lineBC.p2());
    bisectorBC.setAngle(lineBC.normalVector().angle());

    bisectorBA = QLineF(lineBA.pointAt(0.5), lineBA.p2());
    bisectorBA.setAngle(lineBA.normalVector().angle());
    bisectorBA.intersect(bisectorBC, &center);

    circle = QRectF(center.x() - rad, center.y() - rad, rad*2, rad*2);

    lineOA = QLineF(center, p1);
    lineOB = QLineF(center, p2);
    lineOC = QLineF(center, p3);


    startAngle = lineOA.angle();
    spanAngle = lineOA.angleTo(lineOC);
    // Make sure that the span angle covers all three points with the second point in the middle
    if(qAbs(spanAngle) < qAbs(lineOA.angleTo(lineOB)) || qAbs(spanAngle) < qAbs(lineOB.angleTo(lineOC)))
    {
        // swap the end point and invert the spanAngle
        startAngle = lineOC.angle();
        spanAngle = 360 - spanAngle;
    }

    int w = 10;
    boundingRectTemp = circle.adjusted(-w, -w, w, w);
}

QRectF ArcGraphicsItem::boundingRect() const
{
    // outer most edges
    return boundingRectTemp;
}

void ArcGraphicsItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
    QPen paintpen;
    painter->setRenderHint(QPainter::Antialiasing);
    paintpen.setWidth(1);
    // Draw arc

    if(isSelected())
    {
        painter->setBrush(Qt::SolidPattern);
        paintpen.setColor(Qt::black);
        painter->setPen(paintpen);
    }
    else
    {
        paintpen.setStyle(Qt::DashLine);
        paintpen.setColor(Qt::black);
        painter->setPen(paintpen);
    }

    QPainterPath path;
    path.arcMoveTo(circle,startAngle);
    path.arcTo(circle, startAngle, spanAngle);

    // Draw points

    if (isSelected())
    {
        // sets brush for end points
        painter->setBrush(Qt::SolidPattern);
        paintpen.setColor(Qt::red);
        painter->setPen(paintpen);

        qreal ptRad = 10;
        painter->drawEllipse(p1, ptRad, ptRad);
        painter->drawEllipse(p2, ptRad, ptRad);
        painter->drawEllipse(p3, ptRad, ptRad);
    }

    painter->setBrush(Qt::NoBrush);
    painter->drawPath(path);
}

QPainterPath ArcGraphicsItem::shape() const
{
    QPainterPath path;
    path.arcMoveTo(circle,startAngle);
    path.arcTo(circle, startAngle, spanAngle);
    return path;
}

希望这有帮助

票数 3

Stack Overflow用户

发布于 2014-11-13 07:36:06

这听起来似乎可以用一些相对简单的数学来解决：

https://www.google.com/search?q=define%20circle%20three%20points

https://math.stackexchange.com/a/213678

二分/v/三点-定义-a-圆

这是我把数学转化为Qt善良的地方

// m_points is a QList<QPointF>
// use math to define the circle
QLineF lineBC(m_points.at(1), m_points.at(2));
QLineF lineAC(m_points.at(0), m_points.at(2));
QLineF lineBA(m_points.at(1), m_points.at(0));
qreal rad = qAbs(lineBC.length()/(2*qSin(qDegreesToRadians(lineAC.angleTo(lineBA)))));

QLineF bisectorBC(lineBC.pointAt(0.5), lineBC.p2());
bisectorBC.setAngle(lineBC.normalVector().angle());

QLineF bisectorBA(lineBA.pointAt(0.5), lineBA.p2());
bisectorBA.setAngle(lineBA.normalVector().angle());

QPointF center;
bisectorBA.intersect(bisectorBC, &center);

qDebug() << rad << center;

QT QGraphicsScene绘图弧

QPainterPath* path = new QPainterPath();
path->arcMoveTo(0,0,50,50,20);
path->arcTo(0,0,50,50,20, 90);
scene.addPath(*path);

把所有这些放在一个很好的小项目中，就会变成这样：

https://github.com/peteristhegreat/ThreePointsCircle

main.cpp

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

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();

    return a.exec();
}

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = 0);
    ~MainWindow();
};

#endif // MAINWINDOW_H

mainwindow.cpp

#include "mainwindow.h"
#include <QGraphicsView>
#include <QGraphicsScene>
#include "graphicsscene.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
    QGraphicsView * view = new QGraphicsView;

    GraphicsScene * scene = new GraphicsScene();
    view->setScene(scene);

    view->setSceneRect(-300,-300, 300, 300);
    this->resize(600, 600);

    this->setCentralWidget(view);
}

MainWindow::~MainWindow()
{

}

graphicsscene.h

#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);
signals:

public slots:

private:
    QList <QPointF> m_points;
};

#endif // GRAPHICSSCENE_H

graphicsscene.cpp

#include "graphicsscene.h"
#include <QDebug>
#include <QGraphicsEllipseItem>
#include <QGraphicsPathItem>
#include <QPainterPath>
#include "qmath.h"

GraphicsScene::GraphicsScene(QObject *parent) :
    QGraphicsScene(parent)
{
    this->setBackgroundBrush(Qt::gray);
}

void GraphicsScene::mouseDoubleClickEvent(QGraphicsSceneMouseEvent * mouseEvent)
{
    qDebug() << Q_FUNC_INFO << mouseEvent->scenePos();
    QGraphicsScene::mouseDoubleClickEvent(mouseEvent);
}

void GraphicsScene::mouseMoveEvent(QGraphicsSceneMouseEvent * mouseEvent)
{
    qDebug() << Q_FUNC_INFO << mouseEvent->scenePos();
    QGraphicsScene::mouseMoveEvent(mouseEvent);
}

void GraphicsScene::mousePressEvent(QGraphicsSceneMouseEvent * mouseEvent)
{
    qDebug() << Q_FUNC_INFO << mouseEvent->scenePos();
    QGraphicsScene::mousePressEvent(mouseEvent);
}

void GraphicsScene::mouseReleaseEvent(QGraphicsSceneMouseEvent * me)
{
    qDebug() << Q_FUNC_INFO << me->scenePos();
    int radius = 20;
    QGraphicsEllipseItem * ellipse = this->addEllipse(me->scenePos().x() - radius, me->scenePos().y() - radius, radius*2, radius*2);

    ellipse->setBrush(Qt::white);
    m_points.append(me->scenePos());
    if(m_points.size() == 3)
    {
        // use math to define the circle
        QLineF lineBC(m_points.at(1), m_points.at(2));
        QLineF lineAC(m_points.at(0), m_points.at(2));
        QLineF lineBA(m_points.at(1), m_points.at(0));
        qreal rad = qAbs(lineBC.length()/(2*qSin(qDegreesToRadians(lineAC.angleTo(lineBA)))));

        QLineF bisectorBC(lineBC.pointAt(0.5), lineBC.p2());
        bisectorBC.setAngle(lineBC.normalVector().angle());

        QLineF bisectorBA(lineBA.pointAt(0.5), lineBA.p2());
        bisectorBA.setAngle(lineBA.normalVector().angle());

        QPointF center;
        bisectorBA.intersect(bisectorBC, &center);

        qDebug() << rad << center;

        bool drawCircle = true;

        QGraphicsEllipseItem * ellipse = new QGraphicsEllipseItem(center.x() - rad, center.y() - rad, rad*2, rad*2);
        if(drawCircle)
            this->addItem(ellipse);

        // add arc
        // this->addItem(path);
        QPainterPath path;
        QLineF lineOA(center, m_points.at(0));
        QLineF lineOC(center, m_points.at(2));
        path.arcMoveTo(ellipse->boundingRect(),lineOA.angle());
        path.arcTo(ellipse->boundingRect(), lineOA.angle(), lineOC.angle() - lineOA.angle());
        QGraphicsPathItem * pathItem = new QGraphicsPathItem(path);
        pathItem->setPen(QPen(Qt::red,10));
        this->addItem(pathItem);

        if(!drawCircle)
            delete ellipse;
        m_points.clear();
    }

    QGraphicsScene::mouseReleaseEvent(me);
}

票数 12

页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持

原文链接：

https://stackoverflow.com/questions/26901540

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