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/
