createImage(int width，int height)问题 [英] Problems with createImage(int width, int height)

问题描述

我有以下代码，作为游戏的一部分，每10毫秒运行一次:

I have the following code, which is run every 10ms as part of a game:

private void gameRender()
{
    if(dbImage == null)
    {
        //createImage() returns null if GraphicsEnvironment.isHeadless()
        //returns true. (java.awt.GraphicsEnvironment)
        dbImage = createImage(PWIDTH, PHEIGHT);
        if(dbImage == null)
        {
            System.out.println("dbImage is null"); //Error recieved
            return;
        }
        else
        dbg = dbImage.getGraphics();
    }

    //clear the background
    dbg.setColor(Color.white);
    dbg.fillRect(0, 0, PWIDTH, PHEIGHT);

    //draw game elements...

    if(gameOver)
    {
        gameOverMessage(dbg);
    }
}

问题在于，即使我尝试定义图像后，它也会输入if语句来检查Image是否为空.我环顾四周，如果GraphicsEnvironment.isHeadless()返回true，似乎createImage()将返回null.

The problem is that it enters the if statement which checks for the Image being null, even after I attempt to define the image. I looked around, and it seems that createImage() will return null if GraphicsEnvironment.isHeadless() returns true.

我不完全了解isHeadless()方法的目的是什么，但是我认为它可能与编译器或IDE有关，因此我尝试了两种方法，两者都得到相同的错误(Eclipse和BlueJ).任何人都知道错误的根源是什么，我该如何解决?

I don't understand exactly what the isHeadless() method's purpose is, but I thought it might have something to do with the compiler or IDE, so I tried on two, both of which get the same error (Eclipse, and BlueJ). Anyone have any idea what the source of the error is, and how I might fix it?

预先感谢

乔纳森

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我正在使用java.awt.Component.createImage(int width，int height).此方法的目的是确保创建并编辑包含游戏玩家视图的图像，该图像以后将通过JPanel绘制到屏幕上.如果有帮助的话，这里还有更多代码:

I am using java.awt.Component.createImage(int width, int height). The purpose of this method is to ensure the creation of, and edit an Image that will contain the view of the player of the game, that will later be drawn to the screen by means of a JPanel. Here is some more code if this helps at all:

public class Sim2D extends JPanel implements Runnable
{

private static final int PWIDTH = 500;
private static final int PHEIGHT = 400;
private volatile boolean running = true;
private volatile boolean gameOver = false;

private Thread animator;

//gameRender()
private Graphics dbg;
private Image dbImage = null;


public Sim2D()
{   
    setBackground(Color.white);
    setPreferredSize(new Dimension(PWIDTH, PHEIGHT));

    setFocusable(true);
    requestFocus(); //Sim2D now recieves key events
    readyForTermination();

    addMouseListener( new MouseAdapter() {
        public void mousePressed(MouseEvent e)
        { testPress(e.getX(), e.getY()); }
    });
} //end of constructor

private void testPress(int x, int y)
{
    if(!gameOver)
    {
        gameOver = true; //end game at mousepress
    }
} //end of testPress()


private void readyForTermination()
{
    addKeyListener( new KeyAdapter() {
        public void keyPressed(KeyEvent e)
        { int keyCode = e.getKeyCode();
            if((keyCode == KeyEvent.VK_ESCAPE) ||
               (keyCode == KeyEvent.VK_Q) ||
               (keyCode == KeyEvent.VK_END) ||
               ((keyCode == KeyEvent.VK_C) && e.isControlDown()) )
            {
                running = false; //end process on above list of keypresses
            }
        }
    });
} //end of readyForTermination()

public void addNotify()
{
    super.addNotify(); //creates the peer
    startGame();       //start the thread
} //end of addNotify()

public void startGame()
{
    if(animator == null || !running)
    {
        animator = new Thread(this);
        animator.start();
    }
} //end of startGame()


//run method for world
public void run()
{
    while(running)
    {
        long beforeTime, timeDiff, sleepTime;

        beforeTime = System.nanoTime();

        gameUpdate(); //updates objects in game (step event in game)
        gameRender(); //renders image
        paintScreen(); //paints rendered image to screen

        timeDiff = (System.nanoTime() - beforeTime) / 1000000;
        sleepTime = 10 - timeDiff;

        if(sleepTime <= 0) //if took longer than 10ms
        {
            sleepTime = 5; //sleep a bit anyways
        }

        try{
            Thread.sleep(sleepTime); //sleep by allotted time (attempts to keep this loop to about 10ms)
        }
        catch(InterruptedException ex){}

        beforeTime = System.nanoTime();
    }

    System.exit(0);
} //end of run()

private void gameRender()
{
    if(dbImage == null)
    {
        dbImage = createImage(PWIDTH, PHEIGHT);
        if(dbImage == null)
        {
            System.out.println("dbImage is null");
            return;
        }
        else
        dbg = dbImage.getGraphics();
    }

    //clear the background
    dbg.setColor(Color.white);
    dbg.fillRect(0, 0, PWIDTH, PHEIGHT);

    //draw game elements...

    if(gameOver)
    {
        gameOverMessage(dbg);
    }
} //end of gameRender()

} //end of class Sim2D

希望这可以帮助您清除一些东西，乔纳森

Hope this helps clear things up a bit, Jonathan

推荐答案

我通常使用BufferedImage而不是createImage(...).

Instead of createImage(...), I usually use a BufferedImage.

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