report on the Lua in the Gaming Industry Roundtable at GDC 2004

[Luiz Henrique de Figueiredo <lhf@...>]

The moderators have kindly shared with us their report. So here it is.
--lhf

            GDC 2004 - Lua in the Gaming Industry Roundtable Report

Moderators

   Jon Burns [1]
   David Eichorn [2]

   Microsoft Game Studios

Abstract

   The embedded programming language Lua is becoming more and more widely
   used  in  the  gaming  industry. The beauty of this language is in its
   simplicity  and  flexibility;  several  games  within  Microsoft  Game
   Studios employ the use of Lua for many aspects of their architectures,
   including  scripting,  game  balancing,  AI  decision  making, driving
   animations,  UI  layout,  and  level  building.  The  purpose  of this
   roundtable  discussion  is  to  bring  developers  from  the  industry
   together to share in their experiences integrating Lua into their game
   projects.  The goal is to spread awareness of the most popular uses of
   Lua  and  to also make any short-comings or pitfalls apparent to those
   developers evaluating the use of Lua in their games.

Session Format

   The  roundtable  was  broken into two sessions. Not knowing the actual
   experience  level of the participants, the discussion topics were wide
   open; anything related to Lua was fair game.

Attendance

   The  first  session  had approximately sixty attendants, primarily all
   developers.   The   second   session   had  approximately  forty  five
   attendants,  again,  primarily  all  developers. The first session had
   many  more active participants, approximately fifteen, as more of this
   group had some good experience working with Lua on their projects. The
   second   group   was   less   experienced;  only  approximately  seven
   participated  actively.  Some attended to share their experience while
   others  simply wanted to learn more about Lua's impact in the industry
   or evaluate it for possible use.

Key Discussion Points

  Lua 4.0 vs. Lua 5.0

   Users  of  both  stated  that  they  have  observed  as  high as a 20%
   performance  improvement when moving to Lua 5.0. It was concluded that
   it  would behoove any teams using older versions of Lua to switch over
   to Lua 5.0, the latest release version.

  Lua vs. Python

   The  comparison  of Lua and Python was a major theme of both sessions.
   The  general  consensus  here  is  that  Lua is much faster, uses less
   memory,  has  a smaller footprint, and is easier to get up and running
   and  hooked  into  a  game  than Python. Python, however, is much more
   scalable  than  Lua.  Python has a good set of modules for specialized
   tasks  which  makes  it  a  good  language  to  use for cross-platform
   development, while in Lua you'd have to write much of it yourself.

   Many  developers  use  both  languages for different purposes - Lua is
   most  often  used for small-scale while Python is used for large-scale
   tasks  (such  as tool development efforts). Lua is often used for game
   scripting,  Python  for  tools. One developer even said he had written
   his Lua debugger in Python!

  Lua vs. XML

   A  question  was posed regarding using Lua or XML for data definition.
   The  general  consensus was that Lua is much more compact and readable
   than  XML.  XML  is  good  for  describing  small  sets  of  data  and
   web-related  data, and it was suggested that a team could use XML as a
   meta-language  to express game data in binary, which would be good for
   cross-platform  development.  Most  agreed  it  is much easier to find
   XML-savvy editors than Lua editors.

  Lua's easy ramp-up time

   Most  developers  heavily  experienced with Lua said Lua is a language
   that developers can learn in about 10 minutes and that non-programmers
   can  pick  up  at  a fairly quick pace. Certain scripting applications
   using  Lua  could be a good way for junior programmers to get into the
   business.

   There  is  good  documentation  for  Lua,  which  aids  in the ramp-up
   process. There is now a Lua Programming book, reference manuals, and a
   good community support web site [3] [4].

  Non-programmers using Lua

   There  was  general  agreement  that  non-programmers - game and level
   designers, perhaps artists - can learn to understand the syntax of the
   language and write small bits of code with excellent results, but that
   learning  how to actually program in Lua is a challenge. The risk here
   is  the higher chance of subtle bugs being introduced into Lua scripts
   from these non-technical people.

   For  example,  some  devs  had problems with their artists not knowing
   good  naming  conventions and programming concepts well enough to do a
   good job in Lua. One suggestion was to use a tool named Ultraedit that
   color-codes  the Lua script - this developer claimed his artists found
   programming in Lua much easier in this editing program.

   It was also suggested that data-driven design support in Lua is better
   for  these  non-technical  people.  One developer suggested creating a
   multi-tiered system that added increasing levels of abstraction - each
   level  increasing  the  ease of use for the non-technical people using
   Lua. He claimed it has worked very effectively in his project.

  Binding Lua to C++

   Many less-experienced Lua users asked about binding Lua with C++. Some
   developers   are   using  the  Luabind  tool  which  does  this  quite
   effectively,  though  some  cautioned  that the compile times are much
   longer.  One  mentioned that the tool ToLua is no longer supported, so
   use  of  it  should  be  transitioned  to  another  automatic  binding
   generation tool. Other tools mentioned included LuaPlus and Swig. Some
   developers  found  it easier to write their own in-house tools to bind
   Lua and C++ because it is quite easy to do.

   The  discussion  produced  this word of caution: the easier it gets to
   bind  Lua to data objects in the game source, the easier it is to fall
   into the trap of binding *everything* to Lua, which is dangerous...

  Issues encountered when using Lua in game development

   The attendees had many suggestions on avoiding pitfalls:

   Avoid  using  Lua  in  "every  frame"  actions  as  performance  drops
   dramatically.  For example, don't use Lua to do animation updates; set
   up  parameters  for  the  animation in Lua and do the updates in C/C++
   code.

   Avoid  using  Lua  for large game development tasks; rather use Lua in
   quick small-scale actions.

   Avoid  using extremely large table sizes as performance drops in table
   access actions.

   Store  state information outside of Lua in C++ objects, only bind when
   necessary.

   Be  careful about what data is bound to Lua. Having careful control of
   this  data can result in a good, stable environment regarding security
   measures.

   Call garbage-collection routines explicitly only when free cycles come
   up.  Some  devs  found  that  Lua  was  doing  garbage  collection  at
   inopportune times.

   One  developer  cautioned against using incremental garbage collection
   as he observed noticeable slowdown. Because it is a new functionality,
   however, this claim wasn't discussed much.

  Good things about Lua

   The  attendees  had  the  following  to say about what appeals to them
   about using Lua:

   Lua  coroutines work "reasonably well" for cooperative multithreading.
   One  developer  said  they have about twice the overhead of a function
   call (negligible), and that having 3-4 works just fine.

   All of the developers love the fact that licensing Lua is so easy, and
   especially so free.

   In  event-based  and  polling  systems, many of the developers claimed
   they observe no noticeable bottlenecks caused by Lua.

   New  features/tools  coming into the Lua scene make it more attractive
   day by day: Lualint and the new standard debugging library provided in
   Lua 5.0.

   All devs unanimously agreed that the support for Lua is great, whether
   off of the Lua homepage or the community sites, etc.

  Experiences applying Lua

   The  group  shared  some  of  their own personal uses of Lua that were
   particularly memorable and successful:

   One  developer  created  a  cutscene  handler  in Lua that managed the
   triggering  of  cutscenes  in  his  game  project. He found it easy to
   manage in Lua.

   One  developer  was  able to setup a record / replay system for all UI
   actions.

   One developer was doing unit code testing in Lua.

   One  developer  was  able  to  derive  game objects in Lua, and assign
   functions  to  these  objects  in order to test their attributes, etc.
   more easily.

   One  developer  integrated Lua with their physics engine to allow more
   accessibility to tweak physics scripts dynamically.

Summary and Conclusions

   This  roundtable  focused  on the hands-on experiences of people using
   Lua  in  the gaming industry. Attendees were encouraged to share their
   personal  experiences  with  Lua  in  order to spread awareness of the
   benefits  and  pitfalls  of  this  embedded language. The two sessions
   accomplished  this goal quite successfully (we as moderators were very
   surprised  at  the interest in Lua in the gaming industry based on the
   number of attendees both days and in the discussion that came about) -
   there  was good conversation in both roundtable sessions that conveyed
   several  things,  most  notably:  1)  The diverse uses of Lua that are
   specific  to  games  development,  2) What not to use Lua for in games
   development,  3)  The  ease  of  ramp up time for users of Lua, and 4)
   Comparisons  against  other  languages and even older releases of Lua.
   This is where most interest lay for both days.

   There  are  definitely  a handful of very experienced Lua users in the
   gaming  industry  that  are  doing  some very impressive work in their
   projects with the language. Future roundtables on this topic can begin
   to  explore more of what the industry would like to see as features of
   the   language   itself  and  how  the  community  support  for  games
   development can expand more effectively...

References

   1. mailto:jkburns AT microsoft.com
   2. mailto:deichorn AT microsoft.com
   3. http://www.lua.org/
   4. http://lua-users.org/wiki/