一个qt/c++ demo,用于显示 Koch Snowflake （科赫雪花） 分形图

#include <QApplication>
#include <QWidget>
#include <QLabel>
#include <QPixmap>
#include <QPainter>

class KochSnowflakeWidget : public QWidget {
public:
    KochSnowflakeWidget(QWidget *parent = nullptr) : QWidget(parent) {
        setFixedSize(400, 400);
    }

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

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

        QPoint p1(50, 350);
        QPoint p2(350, 350);
        drawKochLine(painter, p1, p2, 3, 0);

        QPoint p3(200, 50);
        drawKochLine(painter, p2, p3, 3, 120);

        drawKochLine(painter, p3, p1, 3, -120);
    }

private:
    void drawKochLine(QPainter &painter, const QPoint &p1, const QPoint &p2, int depth, double angle) {
        if (depth == 0) {
            painter.drawLine(p1, p2);
            return;
        }

        double length = QLineF(p1, p2).length() / 3.0;
        double rad = qDegreesToRadians(angle);
        QPoint p3 = p1 + length * QPointF(cos(rad), -sin(rad));
        QPoint p4 = p3 + length * QPointF(cos(rad - M_PI / 3), -sin(rad - M_PI / 3));
        QPoint p5 = p2 - length * QPointF(cos(rad), -sin(rad));

        drawKochLine(painter, p1, p3, depth - 1, angle);
        drawKochLine(painter, p3, p4, depth - 1, angle - 60);
        drawKochLine(painter, p4, p5, depth - 1, angle + 60);
        drawKochLine(painter, p5, p2, depth - 1, angle);
    }
};

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

    QWidget window;
    QLabel imageLabel(&window);
    QPixmap pixmap(":/koch_snowflake.png");
    imageLabel.setPixmap(pixmap);
    imageLabel.setGeometry(50, 50, 300, 300);
    imageLabel.setScaledContents(true);

    KochSnowflakeWidget kochWidget(&window);
    kochWidget.move(450, 50);

    window.resize(800, 400);
    window.show();

    return app.exec();
}