Design: Card

This will be the first of a set of articles that I will write talking about how I designed MTG Forge. (Well 2nd article, the blogger really messes up Java code.) Magic focuses on cards, so I have a Card object. (I capitalize object names, it’s a Java thing.) Card objects are used everywhere that you would have a regular, cardboard card, in hand, in play, in your graveyard. Card objects hold values like card type (Creature, Sorcery), attack, defense, owner, and controller. Card objects don’t really do anything in and of themselves; they just hold a bunch of related values.

Another important class SpellAbility, implements the functionality of all spells and abilities. It has an abstract resolve() method that is overridden, so Wrath of God’s resolve() would destroy everything, got it?

In MTG Forge, Card objects have one or more SpellAbility objects. A generic creature like Eager Cadet, God bless his frail body, has only one SpellAbility. All creatures are spells, so all Card objects hold at least one SpellAbility. The class CardFactory constructs Cards by adding SpellAbilities, and also implementing the core functionality of the card by the resolve() method. (Resolve() is a method so it gets parenthesis. It is just hard to talk about code, without showing code.)

Ok review, Card objects exist in hand, play, grave, and removed from game. Each Card object has at least one SpellAbility. If a creature has an activated ability like Elvish Piper, the Card will have two SpellAbilities, one SpellAbility for the creature spell, and one for the ability. SpellAbility has an abstract resolve() method that implements the card function, it does the work of the card like destroying things or doing damage, etc..

//*************** START *********** START **************************
//note the mana cost was already set, so I can use the same resolve() for both cards
if(cardName.equals("Wrath of God") || cardName.equals("Damnation"))
{
  final SpellAbility spell = new Spell(card)
  {
    public void resolve()
    {
      CardList all = new CardList();
      all.addAll(AllZone.Human_Play.getCards());
      all.addAll(AllZone.Computer_Play.getCards());

      for(int i = 0; i < all.size(); i++)
      {
        Card c = all.get(i);
        if(c.isCreature())
          AllZone.GameAction.destroyNoRegeneration(c);
      }
    }//resolve()
    public boolean canPlayAI()
    {
      return 0 < CardFactoryUtil.AI_getHumanCreature().size();
    }
  };//SpellAbility
  card.clearSpellAbility();
  card.addSpellAbility(spell);
}//*************** END ************ END **************************


//*************** START *********** START **************************
//note, the card object already has a standard summon creature SpellAbility added to it
if(cardName.equals("Thought Courier"))
{
   //Ability_Tap is a subclass of SpellAbility
  final Ability_Tap ability = new Ability_Tap(card)
  {
    public boolean canPlayAI() {return false;}
    public void resolve()
    {
      AllZone.GameAction.drawCard(card.getController());
      AllZone.InputControl.setInput(CardFactoryUtil.input_discard());
    }
  };//SpellAbility
  card.addSpellAbility(ability);
  ability.setDescription("tap: Draw a card, then discard a card.");
  ability.setStackDescription("Thought Courier - draw a card, then discard a card.");
  ability.setBeforePayMana(new Input_NoCost_TapAbility(ability));
}//*************** END ************ END **************************