java - 如何制作 Java Canvas 游戏循环

Question

这个问题已经有答案了:

What is a NullPointerException, and how do I fix it? (12 个回答)

已关闭 6 年前。

我一直在尝试在 Canvas 中创建一个运行 render(Graphics g) 和logic() 的 java 游戏循环，但它不起作用。

我已经尝试制作一个运行这两个函数的脚本，然后再次调用自身来创建循环。

提前致谢。

我尝试过这个:

public class Canvas extends JPanel {
static GraphicsDevice gd = GraphicsEnvironment.getLocalGraphicsEnvironment().getDefaultScreenDevice();
static int width = gd.getDisplayMode().getWidth();
static int height = gd.getDisplayMode().getHeight();
//Get the system time
long lastTime = System.nanoTime();
//Specify how many seconds there are in a minute as a double
//store as a double cause 60 sec in nanosec is big and store as final so it can't be changed
final double ticks = 60D;
//Set definition of how many ticks per 1000000000 ns or 1 sec
double ns = 1000000000 / ticks;    
double delta = 0;

public static void main(String[] args) {
    JFrame frame = new JFrame("Zombie Run");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.add(new Canvas());
    frame.setSize(width, height);
    frame.setVisible(true);
    loop();
}

public static void loop() {
    logic();
    render(g);
    loop();
}
public static void render(Graphics g) {
    System.out.println("Running Render");
    g.setColor(Color.BLUE);
    g.fillRect(0, 0, 800, 500);

}
public static void logic() {
    System.out.println("Logic");

}

}

我从 eclipse 得到的错误是:

Logic
Running Render
Exception in thread "main" java.lang.NullPointerException
    at ZombieGame.Canvas.render(Canvas.java:41)
    at ZombieGame.Canvas.loop(Canvas.java:36)
    at ZombieGame.Canvas.main(Canvas.java:31)

Answer 1

您可以使用Swing Timer 。 while 循环和 Thread.sleep 只会导致 GUI 卡住。

我使用 Timer 类制作了一个示例。它创建一个延迟 42 毫秒的计时器。每次延迟之后，它都会执行 ActionListener 内的代码。该示例在面板上绘制随机矩形，有点像 Linux 屏幕保护程序 :P 我认为您不必太担心我具体是如何做到这一点的，这只是为了说明 Timer可以使用。

import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Random;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;

public class Foo {

    public static void main(String[] args) throws IOException {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                new Foo().createAndShowGUI();
            }
        });
    }

    public void createAndShowGUI() {
        DrawingPanel panel = new DrawingPanel();

        Timer timer = new Timer(42, new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                panel.addNewRectangle();
                panel.repaint();
            }
        });
        timer.start();

        JFrame frame = new JFrame("Example");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setContentPane(panel);
        frame.setSize(800, 600);
        frame.setVisible(true);
    }

    private class GameRectangle extends Rectangle {
        private Color color;

        public GameRectangle(int x, int y, int width, int height, Color color) {
            setBounds(x, y, width, height);
            setColor(color);
        }

        public void draw(Graphics2D context) {
            context.setColor(getColor());
            context.fill(this);
        }

        public Color getColor() {
            return color;
        }

        public void setColor(Color color) {
            this.color = color;
        }
    }

    private class DrawingPanel extends JPanel {
        private final Random RANDOM = new Random();
        private ArrayList<GameRectangle> rectangles;

        public DrawingPanel() {
            setRectangles(new ArrayList<>());
        }

        @Override
        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2 = (Graphics2D) g.create();
            for (GameRectangle rectangle : getRectangles()) {
                rectangle.draw(g2);
            }
            g2.dispose();
        }

        public void addNewRectangle() {
            getRectangles().add(createRandomRectangle());
        }

        private Color createRandomColor() {
            return new Color(RANDOM.nextInt(255), RANDOM.nextInt(255), RANDOM.nextInt(255));
        }

        private GameRectangle createRandomRectangle() {
            return new GameRectangle(RANDOM.nextInt(getWidth()), RANDOM.nextInt(getHeight()), RANDOM.nextInt(420),
                    RANDOM.nextInt(420), createRandomColor());
        }

        public ArrayList<GameRectangle> getRectangles() {
            return rectangles;
        }

        public void setRectangles(ArrayList<GameRectangle> rectangles) {
            this.rectangles = rectangles;
        }
    }

}