使用Graphics2D绘制图像 [英] Painting an Image using Graphics2D

问题描述

我试图用java的Graphics2D在屏幕上绘制图像。这是我正在使用的代码。我希望看到一个图像稳定地在屏幕上移动。目前我可以看到图像，但除非我调整窗口大小，否则它不会移动，在这种情况下，它会移动。我已经勾画出下面的课程。

I'm trying to get an image to paint on the screen using java's Graphics2D. Here is the code I'm using. I want to see an image move steadily across the screen. At the moment I can see the image but it does not move unless I resize the window, in which case it DOES move. I have sketched out the classes below.

 public class Tester extends JFrame {

    private static final long serialVersionUID = -3179467003801103750L;
    private Component myComponent;
    public static final int ONE_SECOND = 1000;
    public static final int FRAMES_PER_SECOND = 20;

    private Timer myTimer;

    public Tester (Component component, String title) {
        super(title);
        myComponent = component;
    }

    public void start () {

        myTimer = new Timer(ONE_SECOND / FRAMES_PER_SECOND, new ActionListener() {
            @Override
            public void actionPerformed (ActionEvent e) {
                repaint();
            }
        });
        myTimer.start();
    }

    @Override
    public void paint (Graphics pen) {
        if (myComponent != null) {
            myComponent.paint(pen);
        }
    }

}

组件传递给Tester的对象是以下类：

The Component object passed to Tester is the following class:

public class LevelBoard extends Canvas implements ISavable {

    private static final long serialVersionUID = -3528519211577278934L;

    @Override
    public void paint (Graphics pen) {
        for (Sprite s : mySprites) {
            s.paint((Graphics2D) pen);
        }
    }

    protected void add (Sprite sprite) {
        mySprites.add(sprite);
    }

我已经确保这个类只有一个我添加的精灵。 Sprite类大致如下：

I have ensured that this class has only one sprite that I have added. The sprite class is roughly as follows:

public class Sprite {

    private Image myImage;
    private int myX, myY;

    public Sprite () {
        URL path = getClass().getResource("/images/Bowser.png");
        ImageIcon img = new ImageIcon(path);
        myImage = img.getImage();

    }

    public void update () {
        myX += 5;
        myY += 5;
    }

    public void paint (Graphics2D pen) {
        update();
        pen.drawImage(myImage, myX, myY,null);
    }

然而，我在屏幕上只看到一个静止的图像。除非调整窗口大小，否则他不会移动。我知道Sprite类中的paint（Graphics2D pen）方法正在以特定间隔被调用（因为Tester类中的Timer）。但是，即使x和y位置每次增加5。精灵不移动。为什么不？我如何解决它？我只是试图测试我的程序的一些其他功能，所以我真的只是需要启动和运行。我并不在乎如何。

However, I see only a stationary image of bowser on the screen. He does not move unless the window is resized. I know that the paint(Graphics2D pen) method in the Sprite class is being called at particular intervals (because of the Timer in the Tester class). However, even though the x and y positions are being incremented by 5 each time. The sprite does not move. Why not? How do I fix it? I'm just trying to test some other features of my program at the moment so I really just need to get this up and running. I don't really care how.

推荐答案

您的代码充满了问题：

1. 不要覆盖 JFrame.paint（），特别是如果不调用 super 。设置一个ContentPane并覆盖它的 paintComponent（）。尽管它看起来很方便，但它通常是一个糟糕的设计，并且没有必要。
   
2. 不要重载 JComponent.paint（），但而是覆盖 JComponent.paintComponent（）（并调用 super ）


3. 一个 JLabel 来显示图像。它更简单。
   
4. 不要混合使用AWT（Canvas）和Swing（JFrame）。坚持摇摆。

1. Don't override JFrame.paint(), especially if not calling super. Set a ContentPane and override its paintComponent(). While it may seem convenient, it is usually a bad design and unnecessary.
2. Don't override JComponent.paint(), but rather override JComponent.paintComponent() (and call super)
3. Use a JLabel to display an image. It's much simpler.
4. Don't mix AWT(Canvas) and Swing (JFrame). Stick to Swing.

下面是一个简单的例子，显示Bowser在框架中移动。 （这很有趣，当你缩小框架大小，并与框架边框击中图像; - ））

Here is a simple example showing a Bowser moving around the frame. (It's funny when you reduce the frame size and hit the image with the frame border ;-))

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Random;

import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.SwingUtilities;
import javax.swing.Timer;
import javax.swing.UnsupportedLookAndFeelException;

public class TestAnimation2 {
    private static final int NB_OF_IMAGES_PER_SECOND = 50;
    private static final int WIDTH = 800;
    private static final int HEIGHT = 600;
    private Random random = new Random();

    private double dx;
    private double dy;

    private double x = WIDTH / 2;
    private double y = HEIGHT / 2;

    protected void initUI() throws MalformedURLException {
        final JFrame frame = new JFrame(TestAnimation2.class.getSimpleName());
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLayout(null);
        final JLabel label = new JLabel(new ImageIcon(new URL("http://www.lemondedemario.fr/images/dossier/bowser/bowser.png")));
        label.setSize(label.getPreferredSize());
        frame.setMinimumSize(label.getPreferredSize());
        frame.add(label);
        frame.setSize(WIDTH, HEIGHT);
        dx = getNextSpeed();
        dy = getNextSpeed();
        Timer t = new Timer(1000 / NB_OF_IMAGES_PER_SECOND, new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                x += dx;
                y += dy;
                if (x + label.getWidth() > frame.getContentPane().getWidth()) {
                    x = frame.getContentPane().getWidth() - label.getWidth();
                    dx = -getNextSpeed();
                } else if (x < 0) {
                    x = 0;
                    dx = getNextSpeed();
                }
                if (y + label.getHeight() > frame.getContentPane().getHeight()) {
                    y = frame.getContentPane().getHeight() - label.getHeight();
                    dy = -getNextSpeed();
                } else if (y < 0) {
                    y = 0;
                    dy = getNextSpeed();
                }
                label.setLocation((int) x, (int) y);

            }
        });
        frame.setVisible(true);
        t.start();
    }

    private double getNextSpeed() {
        return 2 * Math.PI * (0.5 + random.nextDouble());
    }

    public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException,
            UnsupportedLookAndFeelException {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                try {
                    new TestAnimation2().initUI();
                } catch (MalformedURLException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        });
    }
}

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