Getting a runnable program

It's a nice thing to get everything right the first time. I think I have many things working already, among them are characteristic-setting effects, replacement effects, skipping turns, taking extra turns, and more than two players.

But what I don't have is a game, which is rather disappointing. Sometimes, I think "okay I want to really try it out, a real-world situation. just add in the glue that's missing and make a simple GUI", and then I realize how much of the glue is missing.

Even though I have effects, I have neither spells nor abilities. I can't play cards or abilities. I have (vanilla) creatures, but no combat. I haven't even tested zones, not to mention the Stack.

Okay, now that I finished whining, let me say that I'm still on this. I'm not giving up. The last few days, I focused on the tight core of magic. Turn order is done, all with phases, steps and priority. Next comes the zones, excluding the Stack for now. When I'm done with that, I'll try to program playing a land, which is drastically different from playing spells or abilities.

This should be enough "core engine" to let me finally play a game. Draw a card, play a land or not, pass priority back and forth until it's the opponent's turn (myself again, no AI yet), and so forth.
Of course, there are needs besides the core engine. Most obviously, a GUI. The other two that come to my mind are decks, which i have started already, and a "controller". LaternaMagica has a Player class, which handles life points and so on, but there's no way yet to to make decisions. But that's another story ;)

Quick follow-up: an important thing I've forgotten for my to-do list is state-based actions. it would be too bad if a player doesn't die when he has no life (however that should happen without creatures or spells...)

Undo ... and replacement effects!

I finally got time to work on Laterna Magica again. It wasn't that exciting, just adding undo support to all the classes that already existed. While I browsed the classes and looked for actions that I hadn't revised yet, I found the LifeTotal class. Its job is easy: store the number of life points for a player, and whenever it changes, inform listeners.

...except that there are replacement effects. Only because I want to change life points, that doesn't mean it happens! what could be done?

Surprisingly, the solution looks very similar to my undo engine: Every modification is encapsulated into an edit and stored in the engine. If you want to undo something, the undo engine knows what happened, and every single edit knows how to revert itself. For the caller, it's only addListener(myListener), but inside there's new AddListenerEdit(myListener).execute().

Similarly, the replacement engine is the authority for performing replaceable actions, like gaining life. Calling gainLife(amount) really means new LifeEvent(amount).execute().
Execute uses the replacement engine to apply all replacement effects. Those may replace the event with another event, until all are through. The resulting event is then really executed (the implementation method is called execute0).

Edit and ReplaceableEvent are not connected. Both have an execute method, but that's more or less coincidence. Logically, there is a connection. Look at execute0 from LifeEvent:
public void execute0() {
    ((LifeTotalImpl) getPlayer().getLifeTotal()).fireLifeEvent(this);
}


//...and from LifeTotalImpl


void fireLifeEvent(LifeEvent e) {
    CompoundEdit ed = new CompoundEdit(getGame(), true, "Adjust " + getPlayer() + "'s life by "
            + (e.isGained()? "+":"-") + e.getAmount());
   
    new AdjustLifeEdit(e.getChange()).execute();
   
    // Guaranteed to return a non-null array
    Object[] l = listeners.getListenerList();
    // Process the listeners last to first, notifying
    // those that are interested in this event
    boolean gain = e.isGained();
    for(int i = l.length - 2; i >= 0; i -= 2) {
        if(l[i] == LifeListener.class) {
            if(gain) ((LifeListener) l[i + 1]).lifeGained(e);
            else ((LifeListener) l[i + 1]).lifeLost(e);
        }
    }
    ed.end();
}
Two things are of importance here: First, changing the life is done through an edit, so it can be undone. Second, informing the listeners is encapsulated ina compound edit, so that everything related to this event is grouped together.

I'm quite proud about this piece of code; I expected replacement effects to be very hard, but as it turns out, if there are no flaws in this concept, they should be quite easy.

Progress: LaternaCommon

The second thing I've done in the last months is LaternaCommon. It is more or less a collection of useful utilities:

• It provides a single, application-wide TreeProperties object, loaded from a configurable location
• Configures log4j from a properties file, either configured directly, or by naming a property which stores the location
• Provides an error-handling dialog for uncaught exceptions or to invoke manually
• last but not least, it has a tool that can automatically unzip a file inside the jar. this is very useful to init an application on its first launch.
  With this utility, you store a regular zip file inside the jar, and configure a destination directory and a check file on the file system. If the check file is not found on launch, the zip file is unpacked to the specified directory. Any number of zip files can be specified this way.

I really like how these features all integrate: if the properties don't exist, unpack them. then, configure logging using the properties. last, use the logging utilities for error handling.
You can use this, too, for free. However, I haven't yet uploaded a jar'ed version of it.

Okay, that's for now, and don't worry, in the last few days I resumed development of the core program!

Progress: TreeProperties

I just realized that I didn't post anything for about two months. Well, I did do something, and I want to keep you up.

I have to say that code versioning systems like SVN are a great thing. Besides having a backup on the internet, I'm able to trace back my actions in the last two months. You can look here anytime to see what I was coding recently.

My task was to rework the TreeProperties system that i have come up with sometimes. The point behind it is that you can store properties in simple text files and, for example, implement localization this way. Well, java has something like that built in, but my Library allows much more, the biggest pro being that properties can be split over several files and keys are hierarchical. You can read more about - and download - it here.


Then was a long pause, I took a vacation and went skiing. After that, work went on, and I added many features, fixed bugs etc. In a nutshell, what the library is able to do is:

• Store properties in a tree structure of multiple files
  A file can reference another file, which is then parsed in the same way. Thus, any structure of files may be used to realize the needed properties.
• Use hierarchical property-keys, like "/lang/en/save"
  The namespace mechanism is independent of the file structure, i.e. not bound to a directory structure. When a file is referenced, it inherits its referrer's namespace. For example, if you reference a file with the key "/lang/en", its "save" property has the full key "/lang/en/save". However, if you prefer, you can reference the file with the empty key and literally use "/lang/en/save" in the included file for the same result.
• Support for many data types
  Unlike the java Properties class, which only supports unparsed string values, TreeProperties supports many data types out of the box - no more casting and parsing when accessing properties! Data types include all of the java primitive types, String, BigInteger and BigDecimal, Date and Calendar, File, Path and URL. The mechanism of data types is easily extendable. It requires implementing one interface and registering the type - that's it!
  Special attention goes to the Path type - it adds an abstraction to regular java files that allows to use system properties to be substituted in the path. for example, the values "~/file.txt" or "${user.home}/file.txt", interpreted using the path type, both represent the file "file.txt" in the executing user's home directory. Including files (see above) uses the path type to parse the include, therefore the included file may be personalized for each user, allowing him to set preferences without annoying other users.
• Simple access to the API
  Most needs don't go beyond reading and writing existing properties. Therefore there's a class for exactly that - it has convenience methods that return the standard types already cast, allows default values, and supports localization. The only reason to read into the API is if you need to store new properties.
• Easy GUI
  TreeProperties is a background utility that makes a developer's life way easier. However, now and then there's a case when it steps into the foreground. If you want to show a GUI to the user to let him edit the values, don't build it yourself. It's already there! Setting up a GUI with labels and input components to allow the user to edit properties requires a single method call. what you get is a fully layouted swing panel, ready to add to your GUI. The input components are adjusted for the data type - (formatted) text fields, checkboxes and dropdown fields - and initialized to the current value. Changes to the inputs write to the properties object and are therefore available immediately.

I hope you enjoyed the insight and my work - TreeProperties is open source and can be downloaded as a single jar file. More infos about file formats and usage here.

Next time is about the new sibling of the LaternaMagica project, LaternaCommon, which adds even another level of convenience for the developer in the areas of logging, error handling and deployment.