Just a bit of musing

Carter T Shock ctso at umiacs.umd.edu
Thu Feb 27 08:17:54 CET 1997

I'll never understand why mud-folk have an overwhelming need to explicitly
grid the world. That is, determine a minimum feature size (a room, a grid
square, etc.) and then index one description for each cell in the grid.

A quick (I hope) counter-proposal...
One of the major drawbacks to a grid based system is that everything has to
occupy a(some) grid cell(s). An object has to be associated with the room
it is in, and the room has to know about the object. Each room or location
has an independent description, making for inconsistencies (the old bit
where you step suddenly from forest to mountain, the difficulty of
describing a location as a "forested mountain"). It seems to me that what
you really have is a small-scale GIS, so why not use the techniques found
in other GIS implementations?

The digital nature of things means that there has to be at least an
implicit gridding to the system. All that means is that there is some
finite number of locations that any object may occupy. So we'll give
everything a pair of coordinates. To keep it easy we'll go 2-D and use a
pair of 16 bit values for about 4 billion distinct locations. Since we
don't want to explicitly code descriptions for each of the 4 billion
locations, we'll use some spatial data structure (point quadtrees come to
mind) to index objects, critters, and players. It's small, relatively
compact and let's you do neato things like determine the distance to
another object, find the closest object etc.

Implement terrain features as thematic layers. Something simple like a
region quadtree for each terrain type would do nicely. Again, they're small
and efficient. ("one entry" in the region quadtree is the whole forest,
rather than having to mark each individual location as forest/non-forest).
No reason some terrain types can't overlap. Now when a person moves, you
intersect their new location with the various themes. For each one that
qualifies, you send a description. (i.e. if the player's location is
coincident on a region in your forest theme, and the person is "outside",
you add a line to any other descriptions sent that says "Yer in a forest".
If they are "inside" skip the step. Interestingly, you can use this same
kind of trick to let them look out a window)

Now we need rooms. Sticking with quadtrees for the moment, just implement
one that holds rectangles. Each rectangle is a room and has a description
associated with it. 

The nifty bits: You can encode a _lot_ of info in relatively small
structures. The structures can preserve spatial relationships... i.e. if
they throw or shoot something you know if it hits a wall just by extending
a ray from the player's location and testing for intersections in your
"room" structure. Use "windowing" operations in the spatial structures for
area effects. No reason you can't have a thematic layer of non-magic areas,
of lawful and chaotic areas.

The idea extends to 3 dimensions as well, but computational overhead goes
_way_ up. But, if you host your mud on a bruiser machine, no reason not to.

Sorry for the long post,
> From: Nathan Yospe <yospe at hawaii.edu>
> To: Multiple Recipients of MUD Design Mailing List <mud-dev at null.net>
> Subject: Just a bit of musing
> Date: Wednesday, February 26, 1997 7:31 PM
> A thread on rec.games.mud.admin has recently turned to combat

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