使用MIDP2.0开发游戏(1)GameCanvas基础

文章来源：J2ME开发网
MIDP2.0提供了对游戏的强有力支持，通过javax.microedition.lcdui.game包，原来在MIDP1.0中很多需要自己写的功能现在都被当作标准API实现了，包括GameCanvas，Sprite，Layer等等。
我们将使用MIDP2.0编写一个坦克大战的手机游戏，我也是初学J2ME不久，准备边看书边做，争取把这个游戏做出来！J2ME高手请多指点，和我一样学习中的朋友欢迎多多交流！
我们的开发环境为Windows XP SP1 + J2DK1.4 + J2ME WTK2.1 + Eclipse 3.0 + EclipseMe，关于如何配置Eclipse的J2ME开发环境，请参考：
http://blog.csdn.net/mingjava/archive/2004/06/23/24022.aspx
下面是一个最简单的GameCanvas的例子，出自《J2ME & Gaming》：
// MyGameCanvas.java
// 编写Canvas类
import javax.microedition.lcdui.*;
import javax.microedition.lcdui.game.*;

public class MyGameCanvas extends GameCanvas implements Runnable {
private boolean isPlay; // Game Loop runs when isPlay is true
private long delay; // To give thread consistency
private int currentX, currentY; // To hold current position of the 'X'
private int width; // To hold screen width
private int height; // To hold screen height

// Constructor and initialization
public MyGameCanvas() {
super(true);
width = getWidth();
height = getHeight();
currentX = width / 2;
currentY = height / 2;
delay = 20;
}

// Automatically start thread for game loop
public void start() {
isPlay = true;
new Thread(this).start();
}

public void stop() { isPlay = false; }

// Main Game Loop
public void run() {
Graphics g = getGraphics();
while (isPlay) {
input();
drawScreen(g);
try {
Thread.sleep(delay);
}
catch (InterruptedException ie) {}
}
}

// Method to Handle User Inputs
private void input() {
int keyStates = getKeyStates();
// Left
if ((keyStates & LEFT_PRESSED) != 0)
currentX = Math.max(0, currentX - 1);
// Right
if ((keyStates & RIGHT_PRESSED) !=0 )
if ( currentX + 5 < width)
currentX = Math.min(width, currentX + 1);
// Up
if ((keyStates & UP_PRESSED) != 0)
currentY = Math.max(0, currentY - 1);
// Down
if ((keyStates & DOWN_PRESSED) !=0)
if ( currentY + 10 < height)
currentY = Math.min(height, currentY + 1);
}

// Method to Display Graphics
private void drawScreen(Graphics g) {
g.setColor(0xffffff);
g.fillRect(0, 0, getWidth(), getHeight());
g.setColor(0x0000ff);
g.drawString("X",currentX,currentY,Graphics.TOP|Graphics.LEFT);
flushGraphics();
}
}
// GameMIDlet.java
// 编写MIDlet
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;

public class GameMIDlet extends MIDlet {
private Display display;
public void startApp() {
display = Display.getDisplay(this);
MyGameCanvas gameCanvas = new MyGameCanvas();
gameCanvas.start();
display.setCurrent(gameCanvas);
}

public Display getDisplay() {
return display;
}

public void pauseApp() {
}

public void destroyApp(boolean unconditional) {
exit();
}

public void exit() {
System.gc();
destroyApp(false);
notifyDestroyed();
}
}
编译后就可以在模拟器中运行了，一个X在屏幕中心，可以用上下左右键移动它。