OpenEuphoria

2. Re: RPG objects

• Posted by David Cuny <dcuny at LANSET.COM> Nov 21, 2001
• 376 views

John McAdam wrote:

> OK, so I got some objects in the RPG laying on the floor
> at x, y coordinates.

Fine, you have X and Y coordinates that are associated with the room the
object is currently in. So:

   the[Dagger][INSIDE] = SomeRoom
   the[Dagger][X] = 10
   the[Dagger][Y] = 20

To draw the items, just see what's in the room:

   -- draw the items in the room
   for item = 1 to length( the )
      if the[item][INSIDE] = currentRoom then
         draw( the[item][X], the[item][Y], the[item][IMAGE] )
      end if
   end for

When the object is being held by something (like the player), you don't use
the X and Y coordinates. At most, you just draw the container it's in. So
picking something up:

   procedure pickUp( integer item )
      the[item][INSIDE] = Player
   end procedure

causes it to 'disappear' the next time you draw the room. It's easy to see
if it's in your inventory:

   procedure inventory()
      for item = 1 to length( the )
         if the[item][INSIDE] = Player then
            puts( the[item][NAME] & " " )
         end if
      end for
   end procedure

> Now then what happens when the hero picks them up and puts
> them in a sack in a box in his pack in his boat or wherever,
> or maybe one of the enemies picks up something and puts it in
> his whatever. The objects don't have fixed x,y coordinates
> so how do I keep track of where they are?

You are asking two questions: how do you track what something is inside, and
how do you track the x,y position of that object. Tracking what something is
inside is easy:

   the[Dagger][INSIDE] = Sack
   the[Sack][INSIDE] = Box
   the[Box][INSIDE] = Pack
   the[Pack][INSIDE] = Boat
   the[Player][INSIDE] = Boat

Now, for a Zork sort of game, you do something like that:

   > enter boat
   You are now in the boat. There is a pack here.

   > open pack
   You're not holding a pack.

   > take pack.
   Taken. You are holding a closed pack.

   > open pack
   Opened. The pack contains a closes sack.

   > take sack
   There is no sack in the boat.

   > take sack from pack.
   Taken. You are holding an open pack and a closed sack.

   > open sack
   Opened. You are holding an open pack and an open sack. The
   sack conains a dagger.

   > take dagger from open sack.
   Taken. You are holding an open pack, an open sack and a dagger.

This is the kind of "realism" that grinds adventure games to a halt. But for
a graphical game, there's no issue: you just draw the things that are in the
room, which is the current container. Boats and other vehicles are typically
implemented as special cases here... Anyhoo, when you drop something, you
assign it to the coordinates of where you currently are:

   procedure drop( integer item )
      the[item][INSIDE] = the[Player][INSIDE]
      the[item][X] = the[Player][X]
      the[item][Y] = the[Player][Y]
   end procedure

The next time you draw the room, the item will appear where it was dropped.

-- David Cuny>