绘制图像后，画布不会更新

Question

我正在用Java设计游戏。我使用了java-gaming.org处找到的一些代码，似乎工作奇怪。

当我按照给定的方式运行循环时，它将正确更新我的画布。但是，我并不希望它始终更新我的背景＆＃34;可以这么说。为了解决这个问题，我只运行了一次。现在它似乎运行，但不显示我画的图像。

我上传了运行一次（损坏）的程序截图，程序连续运行（正常运行）。在imgur上查看。

tldr; 一切似乎都在运行，但它并没有在我的框架中显示任何内容。见下面的代码。

package main;

//imports...
import java.awt.Canvas;
import java.awt.Dimension;
import java.awt.Graphics2D;
import java.awt.event.KeyListener;
import java.awt.image.BufferStrategy;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class GameEngine implements Runnable {
    //declare variables...
    final static int B_HEIGHT = 20;
    final static int B_WIDTH = 20;
    private int cellWidth = GameTester.WIDTH / B_WIDTH;
    private int cellHeight = GameTester.HEIGHT / B_HEIGHT;
    protected boolean init = true;
    JFrame frame;
    Canvas canvas;
    BufferStrategy bufferStrategy;
    Board gameBoard;
    Generator gen;

    long desiredFPS = 60;
    long desiredDeltaLoop = (1000 * 1000 * 1000) / desiredFPS;
    boolean running = true;

    public GameEngine(int width, int height) {

        //create the gamespace...
        gameBoard = new Board(B_WIDTH, B_HEIGHT);
        gen = new Generator();

        gen.addWalls(gameBoard);
        agents.Champion champ = new agents.Champion();
        items.Item item = new items.Item();
        gameBoard.placeChampion(champ);
        gameBoard.placeItem(item);

        //frame magic...
        frame = new JFrame("Basic Game");

        JPanel panel = (JPanel) frame.getContentPane();
        panel.setPreferredSize(new Dimension(width, height));
        panel.setLayout(null);

        canvas = new Canvas();
        canvas.setBounds(0, 0, width, height);
        canvas.setIgnoreRepaint(true);

        panel.add(canvas);

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.pack();
        frame.setResizable(false);
        frame.setVisible(true);

        canvas.createBufferStrategy(2);
        bufferStrategy = canvas.getBufferStrategy();

        canvas.requestFocus();
    }

    //actual game mechanics...
    public void run() {

        long beginLoopTime;
        long endLoopTime;
        long currentUpdateTime = System.nanoTime();
        long lastUpdateTime;
        long deltaLoop;

        //game loop...
        while (running) {
            beginLoopTime = System.nanoTime();


            //this draws things
            render();


            lastUpdateTime = currentUpdateTime;
            currentUpdateTime = System.nanoTime();

            //update magic...
            update((int) ((currentUpdateTime - lastUpdateTime) / (1000 * 1000)));

            endLoopTime = System.nanoTime();
            deltaLoop = endLoopTime - beginLoopTime;

            if (deltaLoop <= desiredDeltaLoop) {
                try {
                    Thread.sleep((desiredDeltaLoop - deltaLoop) / (1000 * 1000));
                } catch (InterruptedException e) {
                    // Do nothing
                }
            }
        }
    }

    //creates g object...
    private void render() {
        Graphics2D g = (Graphics2D) bufferStrategy.getDrawGraphics();
        g.clearRect(0, 0, GameTester.WIDTH, GameTester.HEIGHT);
        render(g);
        g.dispose();
        bufferStrategy.show();
    }

    // does nothing important...
    private double x = 0;
    protected void update(int deltaTime) {
        if (GameTester.dbglvl > 1) {
            System.out.println("update called");
        }
        x += deltaTime * 0.2;
        while (x > 500) {
            x -= 500;
        }
    }

    // ACTUAL GAME DRAWING MECHANISM...
    protected void render(Graphics2D g) {
        //first run
        if (init) {
            renderinit(g);
        } else {
            //every other time after first run
        }
    }

    //first run (generates game board)
    protected void renderinit(Graphics2D g) {
        BufferedImage img = null;

        //loop through 2d array
        for (int row = 0; row < gameBoard.getWidth(); row++) {
            for (int col = 0; col < gameBoard.getHeight(); col++) {
                //get image path
                String str = gameBoard.getSpace(row, col).getPath();

                //debug info
                if (GameTester.dbglvl > 1) {
                    System.out.println(gameBoard.getSpace(row, col).getPath());
                }

                //get the image to be rendered
                try {
                    img = ImageIO.read(new File(str));
                } catch (IOException e) {
                    if (GameTester.dbglvl > 0) {
                        System.out
                                .println("image get failed - image specified: "
                                        + str + " ");
                    }
                }

                if (GameTester.dbglvl > 1) {
                    System.out.println("Image Destination: (" + row * cellWidth
                            + ", " + col * cellHeight + ")");
                }

                //draws given image
                g.drawImage(img, row * cellWidth, // DX1
                        col * cellHeight, // DY1
                        (row * cellWidth) + cellWidth, // DX2
                        (col * cellHeight) + cellHeight, // DY2
                        0, // SX1
                        0, // SY1
                        img.getWidth(), // SX2
                        img.getHeight(), // SY2
                        null);

            }
        }
        //done with first time run
        init = false;
        if (GameTester.dbglvl > 0) {
            System.out.println("Board Rendered");
        }
    }
}