Performance of JavaFx Gui vs Swing

I wrote two simple programs, both draw the same Sierpinski Triangle:
One program was implemented using swing, and one using javafx. There is a very significant performance difference, swing implementation being consistently much faster:

(In this test case : Swing over 1 sec. Javafx over 12 seconds)
Is it to be expected or is there something very wrong with my javafx implementation ?

Swing implementation

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.Polygon;
import java.awt.image.BufferedImage;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class SimpleSrpnskTriSw {

    private Triangles triPanel;

    SimpleSrpnskTriSw(int numberOfLevels){

        JFrame frame = new JFrame("Sierpinski Triangles (swing)");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        triPanel = new Triangles();
        frame.add(triPanel, BorderLayout.CENTER);
        frame.pack();

        frame.setResizable(false);
        frame.setVisible(true);

        triPanel.draw(numberOfLevels);
    }

    class Triangles extends JPanel{

        private static final int PANEL_WIDTH =600, PANEL_HEIGHT = 600;
        private static final int TRI_WIDTH= 500, TRI_HEIGHT= 500;
        private static final int SIDE_GAP = (PANEL_WIDTH - TRI_WIDTH)/2;
        private static final int TOP_GAP = (PANEL_HEIGHT - TRI_HEIGHT)/2;

        private int countTriangles;
        private long startTime;
        boolean working;
        private int numberOfLevels = 0;

        Triangles() {

            setPreferredSize(new Dimension(PANEL_WIDTH, PANEL_HEIGHT));
            startTime = System.currentTimeMillis();
            countTriangles = 0;
            working = true;
            draw();
        }

        void draw(int numLevels) {

            numberOfLevels = numLevels;
            working = true;
            draw();
        }

        void draw() {

            startTime = System.currentTimeMillis();
            countTriangles = 0;

            SwingUtilities.invokeLater(new Runnable() {
                @Override
                public void run() {

                    repaint();
                }
            });
        }

        @Override
        public void paintComponent(Graphics g) {

            super.paintComponent(g);
            g.setFont(new Font("Ariel", Font.PLAIN, 14));

            if(working) {

                g.setColor(getBackground());
                g.fillRect(0,0,PANEL_WIDTH,PANEL_HEIGHT);
                g.setColor(getForeground());

                g.drawString("Working.........", 15, 15);
                working = false;
                return;
            }

            if(numberOfLevels <= 0 ) {
                return;
            }
            Point top = new Point(PANEL_WIDTH/2, TOP_GAP);
            Point left = new Point(SIDE_GAP, TOP_GAP+ TRI_HEIGHT);
            Point right = new Point(SIDE_GAP + TRI_WIDTH, TOP_GAP+ TRI_HEIGHT);

            BufferedImage bi = getBufferedImage(top, left, right);
            Graphics2D g2d = (Graphics2D) g;
            g2d.drawImage(bi,0,0, this);

            g.drawString("Number of triangles: "+ countTriangles, 15, 15);
            g.drawString("Time : "+ (System.currentTimeMillis()- startTime)+ " mili seconds", 15, 35);
            g.drawString("Levels: "+ numberOfLevels, 15, 50);
        }

        private BufferedImage getBufferedImage(Point top, Point left, Point right) {

            BufferedImage bi = new BufferedImage(PANEL_WIDTH,PANEL_HEIGHT,
                                                            BufferedImage.TYPE_INT_ARGB);
            drawTriangle(bi, numberOfLevels, top, left, right);
            return bi;
        }

        private void drawTriangle(BufferedImage bi, int levels, Point top, Point left, Point right) {

            if(levels < 0) {
                return ;
            }

            countTriangles++;
            Graphics g = bi.getGraphics();
            g.setColor(Color.RED);

            Polygon tri = new Polygon();
            tri.addPoint(top.x, top.y);  //use top,left right rather than fixed points
            tri.addPoint(left.x, left.y);
            tri.addPoint(right.x, right.y);
            g.drawPolygon(tri);

            // Get the midpoint on each edge in the triangle
            Point p12 = midpoint(top, left);
            Point p23 = midpoint(left, right);
            Point p31 = midpoint(right, top);

            // recurse on 3 triangular areas
            drawTriangle(bi, levels - 1, top, p12, p31);
            drawTriangle(bi, levels - 1, p12, left, p23);
            drawTriangle(bi, levels - 1, p31, p23, right);
        }

        private Point midpoint(Point p1, Point p2) {

            return new Point((p1.x + p2.x) / 2, (p1.y + p2.y) / 2);
        }
    }

    public static void main(String[] args) {

        new SimpleSrpnskTriSw(13);
    }
}

JavaFx implementation

import javafx.application.Application;
import javafx.application.Platform;
import javafx.concurrent.Task;
import javafx.geometry.Insets;
import javafx.geometry.Point2D;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.canvas.Canvas;
import javafx.scene.canvas.GraphicsContext;
import javafx.scene.image.WritableImage;
import javafx.scene.layout.AnchorPane;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.stage.Stage;

public class SimpleSrpnskTriFx extends Application {

    private final int PADDING = 5;
    private static int numberOfLevels;

    public static void launch(String... args){

        numberOfLevels = 8;

        if((args != null) && (args.length > 0)) {

            try {
                int num = Integer.parseInt(args[0]);
                numberOfLevels =  num ;
            } catch (NumberFormatException ex) {
                ex.printStackTrace();
                return;
            }
        }

        Application.launch(args);
    }

    @Override
    public void start(Stage stage) {

        stage.setOnCloseRequest((ae) -> {
            Platform.exit();
            System.exit(0);
        });

        stage.setTitle("Sierpinski Triangles (fx)");

        BorderPane mainPane = new BorderPane();
        mainPane.setPadding(new Insets(PADDING));

        Pane triPanel = new Triangles();

        BorderPane.setAlignment(triPanel, Pos.CENTER);
        mainPane.setCenter(triPanel);

        Scene scene = new Scene(mainPane);

        stage.setScene(scene);
        stage.centerOnScreen();

        stage.setResizable(false);
        stage.show();
    }

    class Triangles extends AnchorPane{

        private static final int PANEL_WIDTH =600, PANEL_HEIGHT = 600;
        private static final int TRI_WIDTH= 500, TRI_HEIGHT= 500;
        private static final int SIDE_GAP = (PANEL_WIDTH - TRI_WIDTH)/2;
        private static final int TOP_GAP = (PANEL_HEIGHT - TRI_HEIGHT)/2;
        private int countTriangles;
        private long startTime;
        private Point2D top, left, right;

        private Canvas canvas;
        private Canvas backgroundCanvas;
        private GraphicsContext gc;

        Triangles(){

            setPrefSize(PANEL_WIDTH, PANEL_HEIGHT);

            canvas = getCanvas();
            backgroundCanvas = getCanvas();
            gc = backgroundCanvas.getGraphicsContext2D();
            getChildren().add(canvas);
            draw(numberOfLevels);
        }

        void draw(int numberLevels) {

            Platform.runLater(new Runnable() {

                @Override
                public void run() {

                    canvas.getGraphicsContext2D().fillText("Working....",5,15);
                    setStartPoints();

                    startTime = System.currentTimeMillis();
                    countTriangles = 0;

                    RunTask task = new RunTask(numberLevels, top, left, right);
                    Thread thread = new Thread(task);
                    thread.setDaemon(true);
                    thread.start();
                }
            });
        }

        private void drawTriangle( int levels, Point2D top, Point2D left, Point2D right) {

            if(levels < 0) {//add stop criteria
                return ;
            }

            gc.strokePolygon( //implementing with strokeLine did not make much difference
                    new double[]{
                            top.getX(),left.getX(),right.getX()
                    },
                    new double[]{
                            top.getY(),left.getY(), right.getY()
                    },
                    3);

            countTriangles++;

            //Get the midpoint on each edge in the triangle
            Point2D p12 = midpoint(top, left);
            Point2D p23 = midpoint(left, right);
            Point2D p31 = midpoint(right, top);

            // recurse on 3 triangular areas
            drawTriangle(levels - 1, top, p12, p31);
            drawTriangle(levels - 1, p12, left, p23);
            drawTriangle(levels - 1, p31, p23, right);
        }

        private void setStartPoints() {

            top = new Point2D(getPrefWidth()/2, TOP_GAP);
            left = new Point2D(SIDE_GAP, TOP_GAP + TRI_HEIGHT);
            right = new Point2D(SIDE_GAP + TRI_WIDTH, TOP_GAP + TRI_WIDTH);
        }

        private Point2D midpoint(Point2D p1, Point2D p2) {

            return new Point2D((p1.getX() + p2.getX()) /
                    2, (p1.getY() + p2.getY()) / 2);
        }

        private void updateGraphics(boolean success){

            if(success) {

                copyCanvas();

                GraphicsContext gc = canvas.getGraphicsContext2D();
                gc.fillText("Number of triangles: "+ countTriangles,5,15);
                gc.fillText("Time : "+ (System.currentTimeMillis()- startTime )+ " mili seconds", 5,35);
                gc.fillText("Levels: "+ numberOfLevels,5,55);
            }

        }

        private Canvas getCanvas() {

            Canvas canvas = new Canvas();
            canvas.widthProperty().bind(widthProperty());
            canvas.heightProperty().bind(heightProperty());
            canvas.getGraphicsContext2D().setStroke(Color.RED);
            canvas.getGraphicsContext2D().setLineWidth(0.3f);

            return canvas;
        }

        private void copyCanvas() {

            WritableImage image = backgroundCanvas.snapshot(null, null);
            canvas.getGraphicsContext2D().drawImage(image, 0, 0);
        }

        /**
         */
        class RunTask extends Task<Void>{

            private int levels;
            private Point2D top, left;
            private Point2D right;

            RunTask(int levels, Point2D top, Point2D left, Point2D right){

                this.levels = levels;
                this.top = top;
                this.left = left;
                this.right = right;

                startTime = System.currentTimeMillis();
                countTriangles = 0;
            }

            @Override public Void call() {

                drawTriangle(levels,top, left, right);
                return null;
            }

            @Override
            protected void succeeded() {

                updateGraphics(true);
                super.succeeded();
            }

            @Override
            protected void failed() {

                updateGraphics(false);
            }
        }
    }

    public static void main(String[] args) {
        launch("13");
    }
}

Answer

The Swing example flattens the image to 600² = 360,000 pixels. In contrast, the JavaFX example strokes almost 2.4 million overlapping polygons when finally rendered. Note that your JavaFX example measures both the time to compose the fractal and the time to render it in the scene graph.

If you want to preserve the strokes comprising the fractal, compose the result in a Canvas, as shown here.

If a flat Image is sufficient, compose the result in a BufferedImage, convert it to a JavaFX Image, and display it in an ImageView, as shown below. The JavaFX result is over a second faster than the Swing example on my hardware.

Because SwingFXUtils.toFXImage makes a copy, a background Task<Image> could continue to update a single BufferedImage while publishing interim Image results via updateValue(). Alternatively, this MandelbrotSet features a Task that updates a WritableImage via its PixelWriter.

import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.Polygon;
import java.awt.image.BufferedImage;
import javafx.application.Application;
import javafx.embed.swing.SwingFXUtils;
import javafx.scene.Scene;
import javafx.scene.image.Image;
import javafx.scene.image.ImageView;
import javafx.scene.image.WritableImage;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

/**
 * @see https://stackoverflow.com/q/44136040/230513
 */
public class BufferedImageTest extends Application {

    private static final int PANEL_WIDTH = 600, PANEL_HEIGHT = 600;
    private static final int TRI_WIDTH = 500, TRI_HEIGHT = 500;
    private static final int SIDE_GAP = (PANEL_WIDTH - TRI_WIDTH) / 2;
    private static final int TOP_GAP = (PANEL_HEIGHT - TRI_HEIGHT) / 2;
    private final int numberOfLevels = 13;
    private int countTriangles;

    @Override
    public void start(Stage stage) {
        stage.setTitle("BufferedImageTest");
        StackPane root = new StackPane();
        Scene scene = new Scene(root);
        root.getChildren().add(new ImageView(createImage()));
        stage.setScene(scene);
        stage.show();
    }

    private Image createImage() {
        BufferedImage bi = new BufferedImage(
            PANEL_WIDTH, PANEL_HEIGHT, BufferedImage.TYPE_INT_ARGB);
        Graphics2D g = bi.createGraphics();
        g.setPaint(Color.white);
        g.fillRect(0, 0, PANEL_WIDTH, PANEL_HEIGHT);
        Point top = new Point(PANEL_WIDTH / 2, TOP_GAP);
        Point left = new Point(SIDE_GAP, TOP_GAP + TRI_HEIGHT);
        Point right = new Point(SIDE_GAP + TRI_WIDTH, TOP_GAP + TRI_HEIGHT);
        g.setColor(Color.red);
        long startTime = System.currentTimeMillis();
        drawTriangle(g, numberOfLevels, top, left, right);
        g.setPaint(Color.black);
        g.drawString("Number of triangles: " + countTriangles, 15, 15);
        g.drawString("Time : " + (System.currentTimeMillis() - startTime) + " ms", 15, 35);
        g.drawString("Levels: " + numberOfLevels, 15, 50);
        WritableImage image = SwingFXUtils.toFXImage(bi, null);
        g.dispose();
        return image;
    }

    private void drawTriangle(Graphics2D g, int levels, Point top, Point left, Point right) {
        if (levels < 0) {
            return;
        }
        countTriangles++;
        Polygon tri = new Polygon();
        tri.addPoint(top.x, top.y);
        tri.addPoint(left.x, left.y);
        tri.addPoint(right.x, right.y);
        g.drawPolygon(tri);

        // Get the midpoint on each edge in the triangle
        Point p12 = midpoint(top, left);
        Point p23 = midpoint(left, right);
        Point p31 = midpoint(right, top);

        // recurse on 3 triangular areas
        drawTriangle(g, levels - 1, top, p12, p31);
        drawTriangle(g, levels - 1, p12, left, p23);
        drawTriangle(g, levels - 1, p31, p23, right);
    }

    private Point midpoint(Point p1, Point p2) {
        return new Point((p1.x + p2.x) / 2, (p1.y + p2.y) / 2);
    }

    public static void main(String[] args) {
        launch(args);
    }

}