J2ME 2D小游戏入门之旅介绍

favoyang
转载请联系作者
响应www.j2medev.com站长mingjava的号召，我也和大家一起分享一下我的经验，希望大家指教。同时www.j2medev.com 欢迎各位高手的原创文章。

前几天看到tony在csdn上发布自己的学习作品“是男人就坚持60s”，觉得创意虽然简单但是却很耐玩，是学习手机游戏制作的入门经典，于是一时兴起，clone了一下，图片依然使用的是tony的图片，纯粹学习之用。如果大家对这个游戏感兴趣可以与tony联系或访问他的blog(他的blog:blog.csdn.net/yesming)。

从发展趋势上说midp2.0是趋势，最便宜的midp2.0手机如ot735i，已经1700元左右；而西门子一年前的高端机cx65，现在也只有2500左右；并且2500-3000这个价位的midp2.0手机有多种选择，西门子、se、N机都有。我个人挺喜欢cx65，如果将来手机制造商成本不断降低，相信1500元的midp将不是梦…当然还要看应用是否丰富了。

言归正传，我们将使用midp 2.0 来开发我们的游戏，代号fly。开发工具jbulider。等文章全写完了，会提供src下载。

目录：

一、游戏的框架

二、完善周边工具类（图象、GameObject、Font）

三、控制飞机的移动

四、加入子弹群，实现碰撞运算

五、实现爆炸效果、并加入道具导弹

六、不足多多，你认为呢？

七、源码

一、游戏的框架

我们的游戏需要一个通用的游戏框架，也方便以后的开发，但实现一个引擎是复杂的。作为初学者如果要你考虑太多的问题，恐怕会让你偏离主线，这里只给出canvas的代码，不理解可以参看本站的另外一篇系列文章《使用MIDP2.0开发游戏》。

使用singlon实现，因为每个gamecanvas都需要很多的内存空间。另外对我们来说，只要改写gameInit()，gameMain(),一次性初始化的代码写在构造函数中。

public class MyGameCanvas extends GameCanvas
implements Runnable, CommandListener{
private static MyGameCanvas instance;
Graphics g;
boolean running;
Thread t;
Command startcmd,exitcmd,restartcmd;
int keystate;
boolean keyevent;
boolean key_up,key_down,key_left,key_right,key_fire;
private boolean allowinput;
public int screenwidth;
public int screenheight;
boolean gameover;
//define your variable here
//define your variable end

protected MyGameCanvas() {
super(true);
g=getGraphics();
running=false;
t=null;
addCommand(startcmd=new Command("start",Command.OK,1));
addCommand(exitcmd=new Command("exit",Command.EXIT,1));
setCommandListener(this);
screenwidth=getWidth();
screenheight=getHeight();

//put your init once code here
//put your init once code end
}

synchronized public static MyGameCanvas getInstance() {
if (instance == null) {
instance = new MyGameCanvas();
System.out.println("new MyGameCanvas");
}
return instance;
}

public void run(){
System.out.println("MyGameCanvas run start");
long st=0,et=0,diff=0;
int rate=50;//16-17 frame per second
while(running){
st=System.currentTimeMillis();
gameinput();
gameMain();
et=System.currentTimeMillis();
diff=et-st;
if(diff<rate){
//System.out.println("Sleep "+(rate-diff));
try {
Thread.sleep(rate - diff);
}
catch (InterruptedException ex) {}
}else{
//System.out.println("rush , and the frame using time: á"+diff);
}
}
System.out.println("MyGameCanvas run end");
}

public void start(){
if(!running){
running=true;
t=new Thread(this);
t.start();
}
}

private void gameMain() {
g.setColor(0,0,0);//clear screen
g.fillRect(0,0,getWidth(),getHeight());

background.paint(g);//draw background
//g.setColor(255,255,255);
//g.drawString("hello",1,1,g.TOP|g.LEFT);
flushGraphics();
}

private void gameInit() {
gameover=false;
gametime=0;
gametimeoffset=System.currentTimeMillis();
allowinput=true;
key_up=key_down=key_left=key_right=key_fire=false;
}

public void stop(){
if(running){
running = false;
}
}

public void commandAction(Command c, Displayable d) {
String cmdstr=c.getLabel();
if(cmdstr.equals("start")){
gameInit();
start();
removeCommand(startcmd);
addCommand(restartcmd=new Command("restart",Command.OK,1));
}else if(cmdstr.equals("restart")){
stop();
while(t.isAlive());
gameInit();
start();
}else if(cmdstr.equals("exit")){
stop();
Navigate.midlet.destroyApp(false);
Navigate.midlet.notifyDestroyed();
}
}

private void gameinput() {
if(allowinput){
keystate=getKeyStates();
keyevent=false;
if((keystate & UP_PRESSED)!=0){//up
key_up=true;keyevent=true;
//deal your unstop job code here
//System.out.println("up press");
//deal your unstop job code end
}else if((keystate & UP_PRESSED)==0){//release key
if(key_up==true){
key_up=false;
//deal your one press-one job code here
//System.out.println("up release");
//deal your one press-one job code end
}
}

if((keystate & DOWN_PRESSED)!=0){//down
key_down=true;keyevent=true;
//deal your unstop job code here

//System.out.println("down press");
//deal your unstop job code end
}else if((keystate & DOWN_PRESSED)==0){//release key
if(key_down==true){
key_down=false;
//deal your one press-one job code here
//System.out.println("down release");
//deal your one press-one job code end
}
}

if((keystate & LEFT_PRESSED)!=0){//left
key_left=true;keyevent=true;
//deal your unstop job code here

//System.out.println("left press");
//deal your unstop job code end
}else if((keystate & LEFT_PRESSED)==0){//release key
if(key_left==true){
key_left=false;
//deal your one press-one job code here
//System.out.println("left release");
//deal your one press-one job code end
}
}

if((keystate & RIGHT_PRESSED)!=0){//right
key_right=true;keyevent=true;
//deal your unstop job code here

//System.out.println("right press");
//deal your unstop job code end
}else if((keystate & RIGHT_PRESSED)==0){//release key
if(key_right==true){
key_right=false;
//deal your one press-one job code here
//System.out.println("right release");
//deal your one press-one job code end
}
}

if((keystate & FIRE_PRESSED)!=0){//fire
key_fire=true;keyevent=true;
//deal your unstop job code here
//System.out.println("fire press");
//deal your unstop job code end
}else if((keystate & FIRE_PRESSED)==0){//release key
if(key_fire==true){
key_fire=false;
//deal your one press-one job code here
//System.out.println("fire release");
//deal your one press-one job code end
}
}
if(!keyevent){
//no keyevent here
//System.out.println("NO KEY press");
//no keyevent end
}
}
}

public static void cleanJob(){
instance=null;
}

}