[messages] [Developers] Roadmap for VASSAL 4

uckelman uckelman at nomic.net
Sun Mar 20 15:57:05 MST 2011

I've been thinking over the past few months about where we should be
heading with the next major release of VASSAL (i.e., VASSAL 4, as
opposed to minor releases like 3.2); I've reached the point now where I
want to write down my thoughts, both to clarify them and to see what
reaction others have.

I've identified four problems which I see at the most serious ones we're

* Editing and designing modules is unnecessarily difficult.

* The game server is a single point of failure and will not scale.

* The interface is clunky and dated.

* The codebase is tangly, hard to modify and debug.

I'll now describe in detail what these problems consist of, and why I've
singled out these problems in particular.

* Editing and designing modules is unnecessarily difficult. Hardly a day
goes by without a question here in the forum about some module design
issue which is conceptually simple, but is difficult to solve due to our
design. (For example, copying pieces from one module to another, while
doable, is something that many module designers will not be able to pull
off, as it involves editing the module buildFile, which is extremely
cryptic.) The trait system, while it makes some easy things easy, also
makes some conceptually easy things mind-bendingly hard. A frequent
complaint that I encounter (e.g., at ConsimWorld and BoardGameGeek) is
that building modules in VASSAL is much harder than in, say, ZunTzu. I
don't find this a fair comparison, in particular because VASSAL modules
generally have far more capabilities than ZunTzu ones; nonetheless, it
should be as easy (or even easier) to create a VASSAL module with
ZunTzu-level capabilities than to create a ZunTzu module.

* The game server is a single point of failure and will not scale. There
are two problems here: First, when the game server is inaccessible from
the internet---whether due to hardware failure, a network connectivity
problem, a power outage---our users aren't able to play in real time.
Our users are quite vocal about this problem. If the game server is
inaccessible, somebody will have complained about it on BoardGameGeek or
ConsimWorld within a little while. As we have no control over when our
ISP has connection issues, or when a big thunderstorm knocks out the
power in Tucson, it's frustrating for us as well as for our users when
this happens. Second---and this is perhaps more serious, though
longer-term---if we had about five times the number of users we have now
connecting to the game server, we might start having issues with
handling all of the server traffic. This isn't the sort of problem where
we could simply put another game server on another pipe to the internet,
as our current server architecture isn't designed to accommodate other
game servers.

* The interface is clunky and dated. This is a collection of problems.
The default Swing Look and Feel is horridly ugly. We also haven't taken
as much care as we should have over the years with making UI
modifications, which has resulted in a lot of parts of the interface
which are cobbled together rather than designed. These make VASSAL look
amateurish. We're also not taking advantage of better display
technology, such as using 3D capabilities for rotation and scaling, than
what existed when VASSAL first started. Some of our competitors are, so
we stand still at our peril.

* The codebase is tangly, hard to modify and debug. Our codebase does
not have a clear separation between GUI and backend. We don't have good
test coverage; partly that's because we only just started writing tests,
but we're also hindered by having a great deal of tightly-coupled,
nearly untestable code. Because of this, it's not as straightforward as
it should be to verify that changes are correct, that bug fixes don't
break anything else, and to add new features. This problem impedes our
progress by making simple tasks take longer than they should, and by
making larger tasks seem to difficult to tackle.

I believe it's essential that we address these four problems for the
long-term health of the project. That said, I have some ideas on how to
address these problems:

* Peer-to-peer communication between clients

* Human-readable XML for modules, saved games, logs

* Model-view separation

* Hooks for change listening scripts

And now I'll explain them in more detail:

* Peer-to-peer communication between clients. This addresses the problem
with the game server being a single point of failure and not being
scalable. What I believe we need to do is make it possible for clients
to host games in an ad-hoc fashion, without necessarily connecting to
the game server. The idea here is that among any group of clients, one
of the clients would act as the game server. The only traffic which
would go to our server would be the notice to add games to the current
games list, and if none of the clients in a game ere capable of acting
as the game server themselves. A P2P library which handles NAT traversal
and shifting the server to a different client if the client currently
hosting the server disconnects is what we'd need for handling this. We
do not want to write this code ourselves, so finding a library to handle
it is imperative. After a bit of poking around, I was unable to find
anything satisfactory. If anyone can suggest some library which does
this, I'd appreciate it.

* Human-readable XML for modules, saved games, logs. This partially
addresses the problem of modules being difficult to design and edit. For
an example of how this would help, have a look at this piece definition
I took from a buildFile:

  <VASSAL.build.widget.PieceSlot entryName="Die" gpid="22" height="0"
width="0">+/null/button;77,130;-50;-15;100;30;Roll      macro;Trigger
die roll and remove Zonk Check;;77,130;;;77\,65,90\,65\  
globalkey;;90,65;88,130;CurrentMap = Trivia Gameboard && Icon =
ZCB;false;1;true;true;;Kill Zone Check Button;-1\\\    
piece;;;DieButton.png;Die/      \       \\      \\\    

If have some idea of what this will produce, then you're probably one of
twenty people in the whole world. If you can see how to edit this by
hand to fix a problem, then you are probably Tim. :) For virtually
everyone else, this is an impenetrable mess. If I want to copy this to a
different module, or change it in some way that's difficult to do with
the Editor, I'll have very little assurance that I won't completely
botch it.

Instead, if this were made human-readable, we'd have fewer questions to
answer from module designers, we wouldn't have to tell people that
seemingly simple things require them to tediously recreate their work,
etc. What I'm proposing is that we don't use what are essentially binary
blobs in our file formats; instead, every game entity is an XML entity,
and every property is an XML attribute. So, we'd have such things as:

  <piece_type id="42" name="101 Abn">
    <face image="..."/>
    <face image="..."/>

XML like this suggests the right way to edit it, unlike what we have
now. It also makes it possible to process it with other tools, be they
XML editors, XSLT, UNIX text processing tools, or even custom tools
written by others. I believe this solution will reduce module designer
frustration and simplify module construction.

* Model-view separation. This addresses both the interface problems and
the poor state of the codebase. I've mentioned this several times in the
past. In order to make as much of our code testable as possible, we need
to have our classes be loosely coupled. This means using interfaces
rather than concrete classes whenever possible. With regard to the GUI,
it means separating out all GUI code from data-handling code. All GUI
code would be put into Views, which listen for changes to Model classes
and display the effects of those changes as appropriate. This should
make it possible to be rid of many of the threading issues we have now,
as well as to increase our flexibility with respect to the GUI. In
particular, we already have Michael's demo using JOGL for zooming,
panning, and rotation---this could form the basis for a 3D-enabled view.
This project gives us the chance to improve both the interface and the
maintainability of the codebase at the same time. It would also open the
door to creating other types of views. (For example, we could create a
view which recorded game actions as a video. We could also treat the
client-server interface as a view...)

* Hooks for change-listening scripts. This addresses the code quality
and module design problems. This is also what I believe to be the most
radical of the proposals I have. As I mentioned above, the traits system
is an odd beast. It makes some simple things easy for non-programmers,
but it lacks the flexibility of a real programming language, which
drives some people to construct Rube-Goldberg-esque contraptions out of
it when they'd be better served by a small amount of code. We spend a
lot of time answering questions about its unintuitive behavior. Much
frustration results from it. Deep nesting of traits causes bad
performance. I think we should replace the traits system.

What I think we should replace it with is the following:

Each game object you can think of as a bundle of properties. For a
piece, you have such things as which face is up, whether it can be
moved, whether and to whom it is hidden, etc. Traits modify those
properties, or do something as a result of those properties being
modified. Suppose that each game object was able to have
pre-modification and post-modification listeners on its properties. A
pre-modification listener would run when a property was about to be
modified; a post-modification listener would run after a property was
modified. The code in such listeners could be in a scripting language
(BeanShell?) which would have access to the data objects and parts of
the GUI via an API we would define. Furthermore, we would need to make
it possible to hang such listeners off certain GUI elements, such as
menu items.

In this way, many of the traits we have now would be implementable as
very simple pre- or post-modification listeners. For example, Send To
Location would be a 
listener which sets some piece's location. If no existing listener were
adequate to the job, rather than stringing together a complex series of
triggers, a module designer could write a small amount of code to do the

What I'd like to see in the Editor is a list of standard listeners for
common tasks (much like the traits we have now), but the scripting for
which can be edited if the module designer so chooses. I think this
would be an improvement over what we have now, as it would be less
obscure, we could rely on the semantics of a standard scripting language
rather than the somewhat odd semantics we have for expressions now, if
wouldn't force designers to know how to program, but it would provide
more power and flexibility for those who do.

Carrying out these four projects will mean major changes in our
codebase, possibly junking a great deal of existing code. I don't see
this as a bad thing, necessarily, as our old and grotty codebase
contributes to at least two of the problems I described above.

This brings me to a question I'd like to put to everyone, which is, on
one hand, independent of the preceding discussion, but is related
because of the degree to which we'd be rewriting code. The question: Is
Java still the best language in which to do all of this? I don't know
the answer to that. I've long had the impression that Java on the
desktop is not in good shape---we suffer from a lot of Java bugs, which
you can see marked "External" in our bug tracker, and also we're getting
to have a pretty good pile of Java bug workaround code, and lots of
these bugs were reported to Sun/Oracle years ago. I get the impression
that libraries which are not as monolithic as Java don't leave serious
bugs unfixed for multiple years. I also get the impression that
developers using other languages have a lot more flexibility with
respect to shipping current versions of libraries which they depend on.
This does not compare favorably with our experience with Macs, for
example, where we're simply stuck with Java 1.5 because Apple won't
update it. So, to sum up, I'm dissatisfied with Java for numerous
reasons. I have some doubts about whether it's the best way forward. I'd
like to know what other people think about this, as well---but I do see
this as independent of the issues raised above. I think we should pursue
the problems and solutions I mentioned regardless, but it's an issue I
wanted to be sure to raise.

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