When delivering on-line content, it is always desirable to ensure that the content is accessible to the widest possible audience. This objective is well-documented in most areas of web development, but when it comes to dealing with 3D scenes and worlds on-line, things are far from straightforward. A variety of formats, proprietary plug-ins and target platforms make delivering 3D content on the web a challenge.

The simplest method of publishing 3D is probably to link straight to a scene file, and rely on a browser plug-in capable of reading it. This approach is limited in that it depends on end-users having such a plug-in installed; and these plug-ins are normally platform-dependant. They also pose problems when trying to fit the object within the webpage; all too often frames are used to compensate, with ugly results.

The best fit to this solution takes the form of the X3D format. X3D specifies a clean XML syntax for 3D worlds, compatible with existing languages and tools, and comes with its own Java implementation, called Xj3D. This open-source codebase contains the code for the scenegraph nodes and also for a browser, allowing 3D objects to be embedded in webpages using Java applets; hence delivering a platform-independent solution as well using a plug-in that is widely supported. I wanted to embed a 3D scene into a webpage for a client, so I found out how to employ Xj3D as an applet.

The Xj3D browser uses OpenGL as the default renderer, which introduces platform-dependent requirements on end-users. The Jogl and Joal libraries depend on native extensions that wouldn’t be known until runtime. Fortunately, there is a mechanism using Java Web Start to embed an applet within Web Start, which determines the user’s platform and downloads the relevant libraries, called applet launcher. Using this mechanism, it is possible to run native code, while coding the applet in a platform-independent way.

First of all, some straightforward Java is used to define the applet which we intend to embed, which has the task of setting up the Xj3D browser. This code was based on the example from xj3d.org.
package com.yourserver.applet;

import java.applet.Applet;
import java.awt.*;
import java.util.HashMap;

import org.web3d.x3d.sai.*;
import org.xj3d.sai.*;
import org.web3d.vrml.scripting.external.sai.*;

public class XJ3DApplet extends Applet {

ExternalBrowser browser;

public XJ3DApplet() {
}

public void init() {
setLayout(new BorderLayout());
browser = getBrowser();
loadScene();
}

// Generate the browser
private ExternalBrowser getBrowser() {
HashMap requestedParameters = new HashMap();
requestedParameters.put(“Xj3D_ConsoleShown”, Boolean.TRUE);
requestedParameters.put(“Xj3D_LocationShown”, Boolean.FALSE);

X3DComponent comp = BrowserFactory.createX3DComponent(requestedParameters);
Xj3DBrowser browser = (Xj3DBrowser) comp.getBrowser();

setBackground(Color.blue);
add((Component) comp, BorderLayout.CENTER);
setVisible(true);

return browser;
}

// Create the scene implementation and add it to the world
private void loadScene() {
X3DScene mainScene = browser.createX3DFromURL(new String[] {getParameter(“modelURL”)});
browser.replaceWorld(mainScene);
}
}
This class can then be packaged up into a jar, ready to be deployed. This class would also be the place to hook into the browser for any SAI-scripting, or to pass other parameters to the browser, such changing cursors or the taskbar look + feel.

The next stage was to obtain the Xj3D libraries to deploy alongside the applet. These can be found on xj3d.org. Xj3D provides a jar file to contain the runtime used with applets, packaging a jar for each X3D profile seperately. You will need to choose which jar file is appropriate for your scene; I was using an immersive scene with touch sensors, so I needed xj3d-immersive-applet-av3d_2.0.0.jar.

Before any of the jars could be used however, it is necessary to sign them using the jarsigner command. If you haven’t already got a keystore, then in order to make jarsigner work you must create a key using the keytool command:
keytool -genkey
Which will prompt you for information necessary to create a self-signed certificate and a key, which defaults to ‘mykey’. I used the domain of the server I would be running off as the common name (it prompts you as ‘Your Name’). Once I had a key, I could sign my applet’s jar and each of the Xj3D jars so that I could host them from my server.
jarsigner -storepass changeit soandso.jar mykey
Once I had signed copies of the latest jar files from xj3d.org, I was ready to define the applet tag. The remaining code resides within inside the applet tag within the HTML itself:
<applet code=”org.jdesktop.applet.util.JNLPAppletLauncher”
width=600
height=400
archive=”http://download.java.net/media/applet-launcher/applet-launcher.jar,

http://www.yourserver.com/jogl.jar,

http://www.yourserver.com/gluegen-rt.jar,

http://www.yourserver.com/joal.jar,

http://www.yourserver.com/uri.jar,

http://www.yourserver.com/vecmath.jar,

http://www.yourserver.com/j3d-org-all_0.9.0.jar,

http://www.yourserver.com/xj3d-immersive-applet-av3d_2.0.0.jar,

http://www.yourserver.com/js.jar,

http://www.yourserver.com/xj3d-sai_2.0.0.jar,

http://www.yourserver.com/xj3d-external-sai_2.0.0.jar,

http://www.yourserver.com/httpclient.jar,

http://www.yourserver.com/aviatrix3d-all_2.0.0.jar,

http://www.yourserver.com/xj3d-script-base_2.0.0.jar,

http://www.yourserver.com/yourbrowserapplet.jar”>

<param name=”codebase_lookup” value=”false”/>
<param name=”subapplet.classname” value=”com.yourserver.applet.XJ3DApplet”/>
<param name=”subapplet.displayname” value=”Your Applet”/>
<param name=”subapplet.image” value=”http://www.yourserver.com/splash.jpg”/>
<param name=”noddraw.check” value=”true”/>
<param name=”progressbar” value=”true”/>

<param name=”jnlpNumExtensions” value=”2″/>
<param name=”jnlpExtension1″
value=”http://download.java.net/media/jogl/builds/archive/jsr-231-webstart-current/jogl.jnlp”/>
<param name=”jnlpExtension2″
value=”http://download.java.net/media/joal/webstart/joal.jnlp”/>

<param name=”modelURL” value=”http://www.yourserver.com/bellsnew.x3d”/>
</applet>
Notice that you can host all the jars yourself. I found that I ran into trouble when I was hosting the applet-launcher jar file; this is related to the necessity of having the native extensions signed by the same source as the applet launcher. I’m sure this is fixable but I didn’t discover how.

One difficulty that I found when using this approach was that the link between Web Start and the applet runtime suppressed errors stemming from the Xj3D browser, making debugging very difficult. I found that it was far more efficient to get my scene working perfectly in the stand-alone browser, which reported errors immediately, before trying to get the applet running. Whenever I had trouble getting the scene to load, it was usually because of a jar file that was missing or not signed correctly.

Now when users visit the HTML page, a Java applet appears that downloads all the necessary software, and runs the Xj3D browser, displaying the 3D content in the most accessible way.