为J2ME开发移动3D游戏之保留模式

　　列表5. 完整的例程代码

package com.kontio;

import javax.microedition.midlet.*;

import javax.microedition.lcdui.*;

import java.lang.IllegalArgumentException;

import java.io.*;

import java.util.*;

import javax.microedition.m3g.*;

public class Example3D extends MIDlet implements CommandListener{

//我们在场景中使用的对象的UserID

static final int POGOROO = 554921620;

static final int CAMERA = 769302310;

static final int TRANSFORM = 347178853;

static final int ROO = 418071423;

private Display myDisplay = null;

private ExampleCanvas myCanvas = null;

private Timer myRefreshTimer = new Timer();

private TimerTask myRefreshTask = null;

private Command exitCommand = new Command("Exit", Command.ITEM, 1);

Graphics3D myGraphics3D = Graphics3D.getInstance();

World myWorld = null;

private AnimationController animRoo = null;

private Group tRoo = null;

private Group tCams = null;

private Group acRoo = null;

private int animLength = 0;

int viewport_x;

int viewport_y;

int viewport_width;

int viewport_height;

public Example3D(){

super();

myDisplay = Display.getDisplay(this);

myCanvas = new ExampleCanvas(this);

myCanvas.setCommandListener(this);

myCanvas.addCommand(exitCommand);

}

public void startApp() throws MIDletStateChangeException{

myDisplay.setCurrent(myCanvas);

try{

　// 从文件中加载World

　myWorld = (World)Loader.load("/pogoroo.m3g")[0];

　getObjects();

　setupAspectRatio();

}

catch(Exception e){

　e.printStackTrace();

}

myRefreshTask = new RefreshTask();

// 调度一个重要执行的计时器以显示出帧速率20fps.

myRefreshTimer.schedule(myRefreshTask, 0, 50);

}

void setupAspectRatio(){

viewport_x = 0;

viewport_y = 0;

viewport_width = myCanvas.getWidth();

viewport_height = myCanvas.getHeight();

Camera cam = myWorld.getActiveCamera();

float[] params = new float[4];

int type = cam.getProjection(params);

if(type != Camera.GENERIC){

　//计算窗口的宽高比例

　float waspect=viewport_width/viewport_height;

　if (waspect
float height = viewport_width/params[1];

viewport_height=(int)height;

viewport_y=(myCanvas.getHeight()-viewport_height)/2;

　}

　else{

float width = viewport_height*params[1];

viewport_width=(int)width;

viewport_x=(myCanvas.getWidth()-viewport_width)/2;

　}

}

}

public void getObjects(){

try{

　tRoo = (Group) myWorld.find(POGOROO);

　tCams = (Group) myWorld.find(CAMERA);

　acRoo = (Group) myWorld.find(TRANSFORM);

　animRoo = (AnimationController) myWorld.find(ROO);

　//取得动画的长度

　AnimationTrack track = acRoo.getAnimationTrack(0);

　animLength = 1000; // 缺省的长度，1秒

　if (track != null){

KeyframeSequence ks = track.getKeyframeSequence();

if (ks != null)

　animLength = ks.getDuration();

　}

}

catch(Exception e){

　e.printStackTrace();

}

}

public void pauseApp(){}

public void destroyApp(boolean unconditional) throws

MIDletStateChangeException{

myRefreshTimer.cancel();

myRefreshTimer = null;

myRefreshTask = null;

}

public void paint(Graphics g){

if(g.getClipWidth() != viewport_width ||

g.getClipHeight() != viewport_height ||

g.getClipX() != viewport_x ||

g.getClipY() != viewport_y){

　g.setColor(0x00);

　g.fillRect(0, 0, myCanvas.getWidth(), myCanvas.getHeight());

}

if ((myGraphics3D != null) && (myWorld != null)){

myGraphics3D.bindTarget(g);

myGraphics3D.setViewport(viewport_x, viewport_y, viewport_width, viewport_height);

myGraphics3D.render(myWorld);

myGraphics3D.releaseTarget();

}

}

public void commandAction(Command cmd, Displayable disp)

{

if (cmd == exitCommand){

　try{

destroyApp(false);

notifyDestroyed();

　}

　catch(Exception e){

e.printStackTrace();

　}

}

}

private class RefreshTask extends TimerTask{

public void run(){

　if(myCanvas !=null && myGraphics3D != null && myWorld != null{

int startTime = (int)System.currentTimeMillis();

int validity = myWorld.animate(startTime);

myCanvas.repaint(viewport_x, viewport_y,

viewport_width, viewport_height);

　}

}

}

class ExampleCanvas extends Canvas{

Example3D myRooMIDlet;

int i = 0;

ExampleCanvas(Example3D Testlet) { myRooMIDlet = Testlet; }

void init() { }

void destroy() { }

protected void paint(Graphics g) { myRooMIDlet.paint(g); }

protected void keyPressed(int i) { }

protected void keyReleased(int i) { }

protected void keyRepeated(int i) { }

protected void pointerDragged(int x, int y) { }

protected void pointerPressed(int x, int y) { }

protected void pointerReleased(int x, int y) { }

}

}

　　九、运行在模拟器中的例程

　　图1展示了例程在WTK模拟器中运行的结果。图中的袋鼠和田地看上去棒极了。如果设计者选择对其中任何对象改变一下的话，可以用the3D工具来完成，而在例程MIDlet中不需要作任何变化。

图1 例程在模拟器中运行的结果

　　十、结论

　　现在，你又看到一种使用JSR 184（也称移动3D API）的更高级的方式来创建3D应用程序。在保留模式下，设计者可以使用现有的3D建模工具来创建3D世界和其中的对象，然后把这些模型输出到M3G文件中。之后，应用程序只需装入该模型并在屏幕上绘制3D世界的视图即可。

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