QGraphicsItem画空心图形

最新推荐文章于 2025-06-29 17:29:37 发布

gdizcm

最新推荐文章于 2025-06-29 17:29:37 发布

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分类专栏： QT实用笔记文章标签：空心QGraphicsItem

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本文介绍如何使用Qt的QGraphicsItem类族绘制空心矩形和椭圆，并通过实现shape函数利用QPainterPathStroker达到描边效果。文中提供了具体的代码实现，包括响应鼠标悬停事件以改变描边宽度。

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用QGraphicsItem类族画出的图形通常都是一个区域（实心的），比如画个圆或者画个矩形。那如果想画个矩形框或者圆形框呢？可以用如下方法，直接上代码

头文件

#include <QGraphicsScene>
#include <QGraphicsRectItem>
#include <QGraphicsPathItem>
#include <QGraphicsEllipseItem>

namespace Ui {
class Widget;
}

class MyRectItem : public QGraphicsRectItem
{
public:
    MyRectItem(const QRectF &rect, QGraphicsItem *parent = 0);
    MyRectItem(qreal x, qreal y, qreal w, qreal h, QGraphicsItem *parent = 0);
    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);

    QPainterPath shape() const;

protected:
    void hoverEnterEvent(QGraphicsSceneHoverEvent *event);
    void hoverLeaveEvent(QGraphicsSceneHoverEvent *event);

private:
    bool isHovered;
};

class MyEllipseItem : public QGraphicsEllipseItem
{
public:
    MyEllipseItem(const QRectF &rect, QGraphicsItem *parent = 0);
    MyEllipseItem(qreal x, qreal y, qreal w, qreal h, QGraphicsItem *parent = 0);
    QRectF boundingRect() const;
    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);

    QPainterPath shape() const;

protected:
    void hoverEnterEvent(QGraphicsSceneHoverEvent *event);
    void hoverLeaveEvent(QGraphicsSceneHoverEvent *event);

private:
    bool isHovered;
    QRectF rect;
};

源文件

#include <QPainterPath>
#include <QPainterPathStroker>

MyRectItem::MyRectItem(const QRectF &rect, QGraphicsItem *parent)
    : QGraphicsRectItem(rect, parent)
{
    this->isHovered = false;
    setFlag(QGraphicsItem::ItemIsSelectable);
    setAcceptHoverEvents(true);
}

MyRectItem::MyRectItem(qreal x, qreal y, qreal w, qreal h, QGraphicsItem *parent)
    : QGraphicsRectItem(x, y, w, h, parent)
{
    this->isHovered = false;
    setFlag(QGraphicsItem::ItemIsSelectable);
    setAcceptHoverEvents(true);
}

void MyRectItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
    QPen pen;
    if (this->isSelected())
    {
        pen.setColor(Qt::red);
    }
    else
    {
        pen.setColor(Qt::green);
    }
    if (this->isHovered)
    {
        pen.setWidth(4);
    }
    else
    {
        pen.setWidth(2);
    }
    painter->setPen(pen);
    painter->drawRect(this->boundingRect());
}

QPainterPath MyRectItem::shape() const
{
    QPainterPath temp;
    temp.addRect(this->boundingRect());
    QPainterPathStroker pathStroker;

    QPainterPath path = pathStroker.createStroke(temp);
    return path;
}

void MyRectItem::hoverEnterEvent(QGraphicsSceneHoverEvent *event)
{
    this->isHovered = true;
    prepareGeometryChange();
}

void MyRectItem::hoverLeaveEvent(QGraphicsSceneHoverEvent *event)
{
    this->isHovered = false;
    prepareGeometryChange();
}

MyEllipseItem::MyEllipseItem(const QRectF &rect, QGraphicsItem *parent)
    : QGraphicsEllipseItem(rect, parent)
{
    this->isHovered = false;
    setFlag(QGraphicsItem::ItemIsSelectable);
    setAcceptHoverEvents(true);
    this->rect = rect;
}

MyEllipseItem::MyEllipseItem(qreal x, qreal y, qreal w, qreal h, QGraphicsItem *parent)
    : QGraphicsEllipseItem(x, y, w, h, parent)
{
    this->isHovered = false;
    setFlag(QGraphicsItem::ItemIsSelectable);
    setAcceptHoverEvents(true);
    this->rect.setX(x);
    this->rect.setY(y);
    this->rect.setWidth(w);
    this->rect.setHeight(h);
}

QRectF MyEllipseItem::boundingRect() const
{
    return this->rect;
}

void MyEllipseItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
    QPen pen;
    if (this->isSelected())
    {
        pen.setColor(Qt::red);
    }
    else
    {
        pen.setColor(Qt::green);
    }
    if (this->isHovered)
    {
        pen.setWidth(4);
    }
    else
    {
        pen.setWidth(2);
    }
    painter->setPen(pen);
    painter->drawEllipse(this->rect);
}

QPainterPath MyEllipseItem::shape() const
{
    QPainterPath temp;
    temp.addEllipse(this->boundingRect());
    QPainterPathStroker pathStroker;

    QPainterPath path = pathStroker.createStroke(temp);
    return path;
}

void MyEllipseItem::hoverEnterEvent(QGraphicsSceneHoverEvent *event)
{
    this->isHovered = true;
    prepareGeometryChange();
}

void MyEllipseItem::hoverLeaveEvent(QGraphicsSceneHoverEvent *event)
{
    this->isHovered = false;
    prepareGeometryChange();
}

程序中包括一个矩形类和一个椭圆形类，选中会变色，悬停会变粗。

通过实现shape函数，使用QPainterPathStroker来画图形的外框，这样画出的图像就是空心的。

测试代码：

在scene上添加图形:

MyRectItem *itemRect = new MyRectItem(10, 10, 100, 100);
scene->addItem(itemRect);
MyRectItem *item2 = new MyRectItem( 20, 20, 120, 120);
scene->addItem(item2);

MyEllipseItem *item3 = new MyEllipseItem(30, 30, 50, 50);
scene->addItem(item3);

MyEllipseItem *item4 = new MyEllipseItem(50, 50, 100, 80);
scene->addItem(item4);