QGraphicsItem画五角星 C++

以下是使用QPainter和QPolygonF绘制五角星的示例代码：

#include <QGraphicsItem>
#include <QPainter>

class StarItem : public QGraphicsItem
{
public:
    StarItem(QGraphicsItem *parent = nullptr) : QGraphicsItem(parent)
    {
        // 设置item的尺寸
        setFlag(QGraphicsItem::ItemIsSelectable);
        setFlag(QGraphicsItem::ItemIsMovable);
        setFlag(QGraphicsItem::ItemSendsGeometryChanges);
        setCacheMode(DeviceCoordinateCache);
        setZValue(-1);
    }

    QRectF boundingRect() const override
    {
        // 返回item的边界矩形
        return QRectF(-50, -50, 100, 100);
    }

    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget) override
    {
        // 绘制五角星
        painter->setRenderHint(QPainter::Antialiasing);
        painter->setPen(Qt::NoPen);
        painter->setBrush(Qt::red);

        const qreal r = 40;
        const qreal deg = M_PI / 180.0;
        QVector<QPointF> points;
        for (int i = 0; i < 5; ++i) {
            const qreal x = 50 + r * qSin(72 * i * deg);
            const qreal y = 50 - r * qCos(72 * i * deg);
            points << QPointF(x, y);
        }
        const QPolygonF polygon(points);
        painter->drawPolygon(polygon);
    }

    QVariant itemChange(GraphicsItemChange change, const QVariant &value) override
    {
        // 拖拽item时更新边界矩形
        if (change == ItemPositionChange) {
            QRectF newRect = boundingRect();
            newRect.translate(value.toPointF());
            return newRect.topLeft();
        }
        return QGraphicsItem::itemChange(change, value);
    }
};

将此类添加到场景中后，将会绘制一个红色的五角星。