java - 这个小程序游戏循环有什么问题？

Question

看起来这个小程序只会在窗口大小调整或最小化时绘制和更新 DRAWS。所以小程序不会一直重画，而只会在操作窗口时重画。

我在这里做错了什么吗？

我正在关注此处呈现的游戏循环:http://www3.ntu.edu.sg/home/ehchua/programming/java/J8d_Game_Framework.html

代码在这里:

package newapplet;

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class GameApplet extends JApplet {     // main class for the game as a Swing application

// Define constants for the game
static final int CANVAS_WIDTH = 493;    // width and height of the game screen
static final int CANVAS_HEIGHT = 411;
static final int UPDATE_RATE = 4;    // number of game update per second
static final long UPDATE_PERIOD = 1000000000L / UPDATE_RATE;  // nanoseconds

static int DRAWS = 0;
// ......

// Enumeration for the states of the game.
public enum gameState {
  INITIALIZED, CONNECTING, PLAYING, DISCONNECTED
}

private gameState state;

// Define instance variables for the game objects
// ......
// ......

// Handle for the custom drawing panel
private GameCanvas canvas;

// Constructor to initialize the UI components and game objects
public GameApplet() {
  // Initialize the game objects
  gameInit();

  // UI components
  canvas = new GameCanvas();
  canvas.setPreferredSize(new Dimension(CANVAS_WIDTH, CANVAS_HEIGHT));
  this.setContentPane(canvas);

  // Other UI components such as button, score board, if any.
  // ......

  this.setVisible(true);
}

// All the game related codes here

// Initialize all the game objects, run only once in the constructor of the main class.
public void gameInit() {
  // ...... 
  state = gameState.INITIALIZED;
}

// Shutdown the game, clean up code that runs only once.
public void gameShutdown() {
  // ...... 
   state = gameState.DISCONNECTED;
}

// To start and re-start the game.
public void gameStart() { 
  // Create a new thread
  Thread gameThread =  new Thread() {
     // Override run() to provide the running behavior of this thread.
     @Override
     public void run() {
        gameLoop();
     }
  };
  // Start the thread. start() calls run(), which in turn calls gameLoop().
  gameThread.start();
}

// Run the game loop here.
private void gameLoop() {
  // Regenerate the game objects for a new game
  // ......
  //state = State.PLAYING;

  // Game loop
  long beginTime, timeTaken, timeLeft;
  while (true) {
     beginTime = System.nanoTime();
     if (state == gameState.DISCONNECTED) break;  // break the loop to finish the current play
     if (state == gameState.PLAYING) {
        // Update the state and position of all the game objects,
        // detect collisions and provide responses.
        gameUpdate();
     }
     // Refresh the display
     repaint();
     // Delay timer to provide the necessary delay to meet the target rate
     timeTaken = System.nanoTime() - beginTime;
     timeLeft = (UPDATE_PERIOD - timeTaken) / 1000000L;  // in milliseconds
     if (timeLeft < 10) timeLeft = 10;   // set a minimum
     try {
        // Provides the necessary delay and also yields control so that other thread can do work.
        Thread.sleep(timeLeft);
     } catch (InterruptedException ex) { }
  }
}

// Update the state and position of all the game objects,
// detect collisions and provide responses.
public void gameUpdate() { 

}

// Refresh the display. Called back via rapaint(), which invoke the paintComponent().
private void gameDraw(Graphics2D g2d) {
  switch (state) {
     case INITIALIZED:
    g2d.setColor (Color.red); 
    g2d.drawString ("init",20,20);
    break;
     case PLAYING:
    g2d.setColor (Color.red); 
    g2d.drawString ("play",20,20);
    break;
  case CONNECTING:
    g2d.setColor (Color.red); 
    g2d.drawString ("connecting",20,20);
    break;
  case DISCONNECTED:
    g2d.setColor (Color.red); 
    g2d.drawString ("disconnect",20,20);
    break;
  }

  g2d.setColor (Color.GREEN); 
  g2d.drawString ("Re-paint: " + DRAWS,30,30);
  this.DRAWS++;
  // ...... 
}

// Process a key-pressed event. Update the current state.
public void gameKeyPressed(int keyCode) {
  switch (keyCode) {
     case KeyEvent.VK_UP:
        // ......
        break;
     case KeyEvent.VK_DOWN:
        // ......
        break;
     case KeyEvent.VK_LEFT:
        // ......
        break;
     case KeyEvent.VK_RIGHT:
        // ......
        break;
  }
}

// Process a key-released event.
public void gameKeyReleased(int keyCode) {  }

// Process a key-typed event.
public void gameKeyTyped(char keyChar) {  }

// Other methods
// ......

// Custom drawing panel, written as an inner class.
class GameCanvas extends JPanel implements KeyListener {
  // Constructor
  public GameCanvas() {
     setFocusable(true);  // so that can receive key-events
     requestFocus();
     addKeyListener(this);
  }

  // Override paintComponent to do custom drawing.
  // Called back by repaint().
  @Override
  public void paintComponent(Graphics g) {
     Graphics2D g2d = (Graphics2D)g;
     super.paintComponent(g2d);   // paint background
     setBackground(Color.BLACK);  // may use an image for background

     // Draw the game objects
     gameDraw(g2d);
  }

  // KeyEvent handlers
  @Override
  public void keyPressed(KeyEvent e) {
     gameKeyPressed(e.getKeyCode());
  }

  @Override
  public void keyReleased(KeyEvent e) {
     gameKeyReleased(e.getKeyCode());
  }

  @Override
  public void keyTyped(KeyEvent e) {
     gameKeyTyped(e.getKeyChar());
  }
}

// main
public static void main(String[] args) {
  // Use the event dispatch thread to build the UI for thread-safety.
  SwingUtilities.invokeLater(new Runnable() {
     @Override
     public void run() {
        new GameApplet();
     }
  });
}
}

Answer 1

快速浏览一下该代码，我可以看到您正在事件调度线程之外调用 repaint()，这可能会导致像您所看到的那样的问题。 javax.swing.SwingUtilties.invokeAndWait(Runnable r) 将允许您将 repaint() 调用放在 EDT 上。

http://docs.oracle.com/javase/tutorial/uiswing/concurrency/dispatch.html