像素编程：未在pixelWriter中的像素上设置颜色

Question

我刚刚开始学习在Java中逐像素制作图形。但是，我不知道如何写像素。它只是显示灰色屏幕。有人可以帮我解决这个问题吗？

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package pixelprogramming;

import java.util.Random;
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.image.Image;
import javafx.scene.image.ImageView;
import javafx.scene.image.PixelWriter;
import javafx.scene.image.WritableImage;
import javafx.scene.layout.StackPane;
import javafx.scene.paint.Color;
import javafx.stage.Stage;

/**
 *
 * @author Ish Chhabra
 */


public class PixelProgramming extends Application {

    @Override
    public void start(Stage primaryStage) {
        StackPane root = new StackPane();
        root.getChildren().add(new ImageView(createImage(300, 250)));

        Scene scene = new Scene(root, 300, 250);

        primaryStage.setTitle("Hello World!");
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    public Image createImage(int width, int height) {
        WritableImage img = new WritableImage(width, height);
        PixelWriter pw = img.getPixelWriter();
        Random rnd = new Random();

        for(int y = 0; y < height; y++) {
            for(int x = 0; x < width; x++) {
                 pw.setColor(x, y, Color.rgb(rnd.nextInt(256), rnd.nextInt(256), rnd.nextInt(256)));
            }
        }
        return img;
    }

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        launch(args);
    }
}