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<H1>[MUD-Dev] Re: Stack-Based NPC AI</H1>
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<LI><em>To</em>: <A HREF="mailto:mud-dev#kanga,nu">mud-dev#kanga,nu</A></LI>
<LI><em>Subject</em>: [MUD-Dev] Re: Stack-Based NPC AI</LI>
<LI><em>From</em>: Mark Gritter <<A HREF="mailto:mark#erdos,Stanford.EDU">mark#erdos,Stanford.EDU</A>></LI>
<LI><em>Date</em>: Sun, 6 Dec 1998 16:06:47 -0800 (PST)</LI>
<LI><em>Reply-To</em>: <A HREF="mailto:mud-dev#kanga,nu">mud-dev#kanga,nu</A></LI>
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<PRE>
Eli Stevens writes:
>
> Every mob would have a "base state" that makes them act a certain way when
> they have nothing else on their to-do stack. There would also be triggers
> that would push a new to-do action onto the stack. When that action was
> finished, it would pop itself off of the stack, allowing whatever was
> beneath it on the stack to be done.
>
[example snipped]
>
> It seems to me that with some imaginative coding, and careful thought
> to the triggers and actions, a very realistic-ish world could be set
> up... Of course, if there are not enough triggers and actions, the
> mobs might all act the same, but that's better than nothing, right?
>
I played around with something of the sort a while back. A couple issues
I encountered were:
-- Subgoals need to be retracted if the goal they're trying to accomplish
gets met. (For example, if I see Boffo get killed, I no longer need to
go round up my friends and take him out.)
-- Intelligent actors should try to batch their goals together. If I have
to pick up something to eat as well as buy components for a spell, it's
much preferable to do both in one trip rather than having a stack like:
go to food store
buy bread
go to house
eat bread
go to magic store
buy lizard warts
go to house
cast spell
Reordering should be allowed, too: if a goal has two subgoals (A and B),
the character should be able to choose which one to pursue first
and change its mind later (if, for example, a new triggered goal brings it
"closer" to accomplishing B instead of A.)
I feel that the natural structure is more of a tree than a stack.
-- Distraction. If triggers aren't balanced correctly, the character
tends to build large stacks without accomplishing many goals. Some means
of ignoring or collapsing the stack would probably be good.
A related AI/robotics strategy is "subsumption architecture". You
might want to do some searching about that. (The examples I've seen
of subsumption architectures generally don't keep state around--- it's
a fixed set of goals with a fixed ordering, if I remember correctly.)
You might try <URL:<A HREF="http://ai.eecs.umich.edu/cogarch0/subsump/">http://ai.eecs.umich.edu/cogarch0/subsump/</A>>
The "Angband Borg" uses a goal-based (but not stack-based) approach, but
you might find it interesting: <URL:<A HREF="http://www.phial.com/angborg/">http://www.phial.com/angborg/</A>>
As far as I know, most of the AI research for planning deals more with how
to achieve goals than to set them up, unfortunately. Still, the "AI on the
Web" page for Norvig + Russel's AI book might be a good place to start
from that end: <URL:<A HREF="http://www.cs.berkeley.edu/~russell/ai.html">http://www.cs.berkeley.edu/~russell/ai.html</A>>
Mark Gritter
mark#erdos,stanford.edu
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<li><strong><A NAME="00914" HREF="msg00914.html">[MUD-Dev] Re: Stack-Based NPC AI</A></strong>
<ul compact><li><em>From:</em> Par Winzell <zell#alyx,com></li></ul>
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<LI><STRONG><A NAME="00909" HREF="msg00909.html">[MUD-Dev] Stack-Based NPC AI</A></STRONG>
<UL><LI><EM>From:</EM> "Eli Stevens (KiZurich)" <c718157#showme,missouri.edu></LI></UL></LI>
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<ul><li>Thread context:
<BLOCKQUOTE><UL>
<LI><STRONG>[MUD-Dev] Re: Introduction</STRONG>, <EM>(continued)</EM>
<ul compact>
<ul compact>
<LI><strong><A NAME="00945" HREF="msg00945.html">[MUD-Dev] Re: Introduction</A></strong>,
Mik Clarke <a href="mailto:mikclrk#ibm,net">mikclrk#ibm,net</a>, Wed 09 Dec 1998, 07:15 GMT
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</ul>
</ul>
</LI>
<LI><strong><A NAME="00909" HREF="msg00909.html">[MUD-Dev] Stack-Based NPC AI</A></strong>,
Eli Stevens (KiZurich) <a href="mailto:c718157#showme,missouri.edu">c718157#showme,missouri.edu</a>, Sun 06 Dec 1998, 22:38 GMT
<UL>
<LI><strong><A NAME="00910" HREF="msg00910.html">[MUD-Dev] Re: Stack-Based NPC AI</A></strong>,
Richard Woolcock <a href="mailto:KaVir#dial,pipex.com">KaVir#dial,pipex.com</a>, Mon 07 Dec 1998, 00:00 GMT
<UL>
<LI><strong><A NAME="00930" HREF="msg00930.html">[MUD-Dev] Re: Stack-Based NPC AI</A></strong>,
Mik Clarke <a href="mailto:mikclrk#ibm,net">mikclrk#ibm,net</a>, Mon 07 Dec 1998, 21:35 GMT
</LI>
</UL>
</LI>
<LI><strong><A NAME="00911" HREF="msg00911.html">[MUD-Dev] Re: Stack-Based NPC AI</A></strong>,
Mark Gritter <a href="mailto:mark#erdos,Stanford.EDU">mark#erdos,Stanford.EDU</a>, Mon 07 Dec 1998, 00:06 GMT
<UL>
<LI><strong><A NAME="00914" HREF="msg00914.html">[MUD-Dev] Re: Stack-Based NPC AI</A></strong>,
Par Winzell <a href="mailto:zell#alyx,com">zell#alyx,com</a>, Mon 07 Dec 1998, 01:18 GMT
<UL>
<LI><strong><A NAME="00925" HREF="msg00925.html">[MUD-Dev] Re: Stack-Based NPC AI</A></strong>,
David Bennett <a href="mailto:ddt#discworld,imaginary.com">ddt#discworld,imaginary.com</a>, Mon 07 Dec 1998, 20:03 GMT
</LI>
<LI><strong><A NAME="00926" HREF="msg00926.html">[MUD-Dev] Re: Stack-Based NPC AI</A></strong>,
David Bennett <a href="mailto:ddt#discworld,imaginary.com">ddt#discworld,imaginary.com</a>, Mon 07 Dec 1998, 20:05 GMT
</LI>
</UL>
</LI>
</UL>
</LI>
<LI><strong><A NAME="00912" HREF="msg00912.html">[MUD-Dev] Re: Stack-Based NPC AI</A></strong>,
Marc Hernandez <a href="mailto:marc#ias,jb.com">marc#ias,jb.com</a>, Mon 07 Dec 1998, 00:22 GMT
</LI>
</UL>
</LI>
</UL></BLOCKQUOTE>
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