Java 动画不工作

Question

我正在尝试用 Java 制作一个正方形的动画，但是当我按下按键时，正方形会在后面留下一条痕迹。我希望方 block 本身移动时不会像蛇一样留下痕迹。

我该如何解决这个问题？我能做些什么来解决这个问题吗？

这是我的代码:

import java.awt.Canvas;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.image.BufferStrategy;

import javax.swing.JFrame;

public class Main extends Canvas implements KeyListener, Runnable {

    Thread t;
    boolean running = false;

    int x = 200;
    int y = 200;
    int velx;
    int vely;

    public Main() {
        setFocusable(true);
        requestFocus();
        addKeyListener(this);
    }

    public void run() {
        while (running) {
            render();
            tick();
        }
        stop();
    }

    synchronized void start() {
        if (running) return;

        running = true;
        t = new Thread(this);
        t.start();
    }

    synchronized void stop() {
        try {
            t.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.exit(1);
    }

    public void render() {

        BufferStrategy bs = this.getBufferStrategy();
        if (bs == null) {
            createBufferStrategy(3);
            return;
        }
        Graphics g = bs.getDrawGraphics();

        g.setColor(Color.CYAN);
        g.fillRect(x, y, 300, 300);

        g.dispose();
        bs.show();

    }

    public void tick() {
        x += velx;
        y += vely;
    }

    @Override
    public void keyPressed(KeyEvent e) {
        int key = e.getKeyCode(); 
        if (key == KeyEvent.VK_RIGHT) {
            velx += 5;
        } else if (key == KeyEvent.VK_LEFT) {
            velx -= 5;
        } else if (key == KeyEvent.VK_DOWN) {
            vely += 5;
        } else if (key == KeyEvent.VK_UP) {
            vely -= 5;
        }
    }

    @Override
    public void keyTyped(KeyEvent e) {}

    @Override
    public void keyReleased(KeyEvent e) {
        velx = 0;
        vely = 0;
    }

    public static void main (String args[]){

        JFrame frame = new JFrame("Animation");
        Main main = new Main();

        frame.setSize(1200, 800);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLocationRelativeTo(null);
        frame.add(main);
        frame.setResizable(false);
        frame.setVisible(true);

        main.start();

    }

}

Answer 1

在绘制具有更新坐标的新正方形之前，您应该始终删除 Canvas 上已绘制的正方形(即用背景颜色覆盖它)。为此，您可以按如下方式修改代码:

int prevX, prevY;

public void render() {
  BufferStrategy bs = this.getBufferStrategy();
  if (bs == null) {
      createBufferStrategy(3);
      return;
  }
  Graphics g = bs.getDrawGraphics();

  // erase the previous square
  g.setColor(getBackground());
  g.fillRect(prevX, prevY, 300, 300);

  // draw the new square
  g.setColor(Color.CYAN);
  g.fillRect(x, y, 300, 300);

  g.dispose();
  bs.show();
}

public void tick() {
  // backup the previous coordinates
  prevX = x;
  prevY = y;

  x += velx;
  y += vely;
}