Making Games in Liblol: Part 6: The Store

While this post title is "The Store", this is really about another component of LibLOL: the "Facts" interface.

In most games, there are things (typically numbers) that you might want to save.  During the play of a single level, you might want to count how many power-ups the player used.  During one interaction with the game (such as playing 18 holes of golf), you might want to keep track of the score on each hole.  You might also want to track some statistics relating to the history of every time the game has been played.

While you can manage most of this using fields in the objects of your game, it's often easier to have a unified interface.  That's where Facts comes in.

Facts come in a few flavors: first of all, we can store numbers related to the current level being played (LevelFacts), to the current interaction with the game (SessionFacts), or with the whole game (GameFacts).  For each of these, we can either put a fact as a string and an integer value, or we can get a fact, again as an integer value.

For the sake of completeness, I'll note that there is one special case for Facts: we can also save and retrieve actors (Goodies, Obstacles, Heroes, Enemies, Projectiles) for the current level, also as LevelFacts.

Getting back to our store example, the main idea is that we can use Actors in the store to represent buttons for things to purchase.  In a level, as we collect coins, the level's internal score increases.  To turn the coins of the level into a Fact, we can do something like this:

            LolCallback sc = new LolCallback() {
                public void onEvent() {
                    int oldCoins = Facts.getGameFact("Coins", 0);
                    int addedCoins = Score.getGoodiesCollected1();
                    Facts.putGameFact("Coins", oldCoins + addedCoins);
                }
            };
            Level.setWinCallback(sc);

Putting that code in our level will say that when the level is won, we'll add the score (score 1, to be precise... remember that we have counters for four different kinds of scores) to the old coin count.

We could get more fancy, for example by having callbacks on our coins so that we could directly add to a specific LevelFact.  But for our example, this is good enough.

What about the store, then?  Well, it's pretty simple: we can have obstacles on a store screen to represent buttons for purchasing power-ups, and then we can have TouchCallbacks on the buttons that subtract from the Facts to make a purchase happen.  Those callbacks should also update other GameFacts to indicate the numbers of power-ups remaining.

Hopefully that's enough information to get you started building a store for your app.  But I do have one question: are integer and Actor Facts enough?  Would String facts be useful?  Let me know in the comments.