如何使用QPainter绘制焦点图标

#include <QtWidgets>

class FocusIconWidget : public QWidget {
public:
    explicit FocusIconWidget(QWidget *parent = nullptr) : QWidget(parent) {}

protected:
    void paintEvent(QPaintEvent *event) override {
        Q_UNUSED(event);

        QPainter painter(this);
        painter.setRenderHint(QPainter::Antialiasing, true);

        // 绘制圆形焦点图标
        painter.setPen(Qt::NoPen);
        painter.setBrush(Qt::red);
        painter.drawEllipse(rect().center(), 50, 50);

        // 绘制内部的白色圆形
        painter.setBrush(Qt::white);
        painter.drawEllipse(rect().center(), 30, 30);
    }
};

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);

    FocusIconWidget widget;
    widget.resize(200, 200);
    widget.show();

    return app.exec();
}