mjbWorld program - Scripting

There are some behaviours built into the core program, but these are very limited, repetitive behavours. These use VRML type Sensors and Interpolators. These work by sending events between the beans.

There is a need to add much more general purpose behaviours. It seems to me that the best way to do this is to support a scripting language in the program. There seem to be a number of such programs availible, see below, so it seems silly to try to re-invent the wheel.

Whatever scripting language is chosen it needs to be able to.

Examples of how this might be used: say you were writing a 3D game, when there was a collision between two objects, this would trigger a script which would alter the scores and start an explosion secuence.

Another example might be to drive an animation sequence.

JPython

JPython looks like a good possibility, in order to try it out I have added JPython support to mjbWorld_beta307. If you select RunJPython under the FILE menu it runs the following method:
public void RunJPython(){
 try {
   String line;
   FileReader fr;
   BufferedReader br;
   File selectedFile = null;
   PythonInterpreter interp = new PythonInterpreter();
   javax.swing.JFileChooser fileChooser = new javax.swing.JFileChooser();
   if (directory == null) directory = new File("//C:");
   int returnvalue = fileChooser.showDialog(null,null);
   if (returnvalue == javax.swing.JFileChooser.APPROVE_OPTION) {
     directory = fileChooser.getCurrentDirectory();
     selectedFile = fileChooser.getSelectedFile();
     fr = new FileReader(selectedFile);
     br = new BufferedReader(fr);
     do {
       line=br.readLine();
       if (line != null) {
         statusMessage(line);
         interp.exec(line);
       }
     } while (line != null);
   }
   fileChooser.setVisible(false);
 } catch (Exception e) {
   System.out.println("mjbFrame.RunJPython error: " + e.toString());
 }
 return;
}

The only problem is that JPython is not Java, so it would be a new language for the users to learn.

Further details at:

http://www.jpython.org/

JPython is an implementation of the high-level, dynamic, object-oriented language Python seamlessly integrated with the Java platform and certified as 100% Pure Java. JPython is freely available for both commercial and non-commercial use and is distributed with source code. JPython supports embedded scripting - Java programmers can add the JPython libraries to their system to allow end users to write simple or complicated scripts that add functionality to the application. Since JPython is certified 100% Pure Java, it can be added to an application without fear of compromising its ability to run on all Java platforms.

Rhino

http://www.mozilla.org/rhino/index.html

Rhino is an implementation of JavaScript written entirely in Java. It gets its name from the animal on the cover of the O'Reilly book about JavaScript.

The Rhino project was started at Netscape in Fall 1997. At the time, Netscape was planning to produce a version of Navigator written entirely in Java and so it needed an implementation of JavaScript written in Java. When Netscape stopped work on "Javagator", as it was called, somehow Rhino escaped the axe (rumor had it that the executives "forgot" it existed). Since then, a couple of major companies (including Sun) have licensed Rhino for use in their products and paid Netscape to do so, allowing us to continue work on it. Now Rhino is planned to be part of several server products from Netscape as well.
Originally, Rhino compiled all JavaScript code to Java bytecodes in generated classfiles. This produced the best performance (often beating the C implementation of JavaScript when run on a JIT), but suffered from two faults. First, compilation time was long since generating Java bytecodes and loading the generated classes was a heavyweight process. Also, the implementation effectively leaked memory since most JVMs don't really collect unused classes or the strings that are interned as a result of loading a class file.

So in Fall of 1998, Rhino added an interpretive mode. The classfile generation code was moved to an optional, dynamically-loaded package. Compilation is faster and when scripts are no longer in use they can be collected like any other Java object.

We've wanted to put Rhino in Mozilla ever since mozilla.org was started, but have been limited by the contracts we signed with licensees. Just recently we received approval from our licensees to make Rhino publicly available as free source, but they requested that we hold back classfile generation for the time being. Considering that Rhino probably wouldn't have existed were it not for their support, I think it's a reasonable request. Most of what makes Rhino appealling can be had even without classfile generation, which is primarily a performance enhancement.

BeanShell

BeanShell is a small, free, embeddable, Java source interpreter with object scripting language features, written in Java. BeanShell executes standard Java statements and expressions, in addition to obvious scripting commands and syntax

see http://www.beanshell.org/

Bean Scripting Framework BSF

For more information about BSF, see http://www.alphaworks.ibm.com/

Bean Markup Language' (BML)

. (www.alphaworks.ibm.com)

Other possible script languages:

http://grunge.cs.tu-berlin.de/~tolk/vmlanguages.html

Adding New tools

We also be able to dynamically add new tools, wizards, etc. to the program. Again this should be done by plugging in a general purpose scripting language. These wizards would be assined to menu items and stored as scripts when the program is saved.


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Arhitecture

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