QGraphicsItem画空心图形_qt paint 画实心矩形

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);

如图所示，鼠标划过时，框内图形可以选中也可以点击。