class Sierpins {

    static void sierpins(DrawingWindow w,
                         int n,                 // niveau de récursion demandé
                         float xa, float ya,    // coordonnées du point A
                         float xb, float yb,    // coordonnées du point B
                         float xc, float yc)    // coordonnées du point B
    {
        if (n == 0) {
            w.drawTriangle(Math.round(xa), Math.round(ya),
                           Math.round(xb), Math.round(yb),
                           Math.round(xc), Math.round(yc));
        } else {
            float xd = (xa + xb) / 2;
            float yd = (ya + yb) / 2;
            float xe = (xb + xc) / 2;
            float ye = (yb + yc) / 2;
            float xf = (xc + xa) / 2;
            float yf = (yc + ya) / 2;
            sierpins(w, n - 1, xa, ya, xd, yd, xf, yf);
            sierpins(w, n - 1, xb, yb, xe, ye, xd, yd);
            sierpins(w, n - 1, xc, yc, xf, yf, xe, ye);
        }
    }

    public static void main(String[] args) {
        DrawingWindow w = new DrawingWindow("Sierpins", 640, 480);
        sierpins(w, 10,
                 w.width / 2.0f, 0, 0, w.height - 1, w.width - 1, w.height - 1);
    }
}