import javafx.animation.KeyFrame;
import javafx.animation.Timeline;
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.canvas.Canvas;
import javafx.scene.canvas.GraphicsContext;
import javafx.scene.layout.StackPane;
import javafx.scene.paint.Color;
import javafx.stage.Stage;
import javafx.util.Duration;

import java.util.Random;

public class Main extends Application {

    final int W = 1200;
    final int H = 800;

    @Override
    public void start(Stage primaryStage) throws Exception{

        Canvas canvas = new Canvas(W, H);

        StackPane stackPane = new StackPane();

        stackPane.getChildren().addAll(canvas);

        GraphicsContext graphicsContext = canvas.getGraphicsContext2D();        

        Timeline t = new Timeline();

        t.getKeyFrames().addAll(new KeyFrame(Duration.ZERO), new KeyFrame(Duration.INDEFINITE));

        t.currentTimeProperty().addListener((observableValue, duration, duration2) -> {

            Random r = new Random();

            graphicsContext.setFill(Color.BLACK);
            graphicsContext.fillRect(0, 0, W, H);

            for(int i = 0; i < 20000; i++){
                graphicsContext.setFill(Color.rgb(r.nextInt(256), r.nextInt(256), r.nextInt(256)));
                graphicsContext.fillOval(r.nextInt(W), r.nextInt(H), 10, 10);
            }
        });
        
        t.playFromStart();
        Scene scene = new Scene(stackPane, W, H);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

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