1.1. Authorship and Copyright

This document is copyright (c) 2001 Peter Jay Salzman, <p@dirac.org>. Permission is granted to copy, distribute and/or modify this document under the terms of the Open Software License, Version 1.1, except for the provisions I list in the next paragraph. I hate HOWTO's that include the license; it's a tree killer. You can read the OSL at http://opensource.org/licenses/osl-1.1.txt.

If you want to create a derivative work or publish this HOWTO for commercial purposes, I would appreciate it if you contact me first. This will give me a chance to give you the most recent version. I'd also appreciate either a copy of whatever it is you're doing or a spinach, garlic, mushroom, feta cheese and artichoke heart pizza.

1.2. Acknowledgements

Thanks to Mike Phillips who commented extensively on the howto. Thanks to Dmitry Samoyloff, <dsamoyloff@yandex.ru>, for translating this document into Russian. It blew my mind when he told me that he was translating my words to Russian. Further thanks goes to:

1. Moritz Muehlenhoff <jmm@Informatik.uni-bremen.de> for sending me updates (even if I'm eternally behind on them...)

2. Frédéric Delanoy for extensive diffs or correcting typos and docbook mistakes

1.3. Latest Versions and Translations

The latest version can be found at http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/lgh/LG-HOWTO or http://www.dirac.org/linux/writing, but this is my own personal working copy. The version at my personal web site might be broken if I'm working on the HOWTO. The version at sourceforge is bleeding edge but guaranteed to be not broken, however it may have glitches, like unfinished paragraphs. :)

The most recent stable version can be found at http://www.tldp.org.

Dmitry Samoyloff <dsamoyloff@mail.ru> is the maintainer of the Russian translation. The most recent version can be found at http://linuxgames.hut.ru/data/docs/HOWTO/LG-HOWTO-ru.html.

2.1. Arcade style

Although arcade games had their heydey in the 80's, they are nonetheless very popular. Nothing will ever replace walking into a dark, crowded and noisy arcade gallery, popping a quarter into your favorite machine and playing an old fashioned game of Space Invaders. Arcade style games attempt to simulate the arcade games themselves. There is such a vast number of these things that it's nearly impossible to enumerate them all, but they include clones of Asteroids, Space Invaders, Pac-Man, Missile Command and Galaxian.

2.2. Card, logic and board games

Computer based card games simulate a card game like poker or solitaire. The program can simulate your opponent(s).

Logic games usually simulate some well known logic puzzle like Master Mind or the game where you have put sliding numbered tiles in order inside a box.

Computer based board games simulate some kind of board game you'd play on a table top with friends, like monopoly, Mille Bourne, chess or checkers. The program can simulate your opponent.

2.3. Text Adventure (aka Interactive Fiction)

Once upon a time, when Apple ][, Commodore, and Atari ruled the world, text adventures were the game of choice of `intelligent folk'. You are given a scenario and can interact with the world you're placed in:

You are in a room.  It is pitch dark and you're likely to be eaten by a grue.
> Light lantern with match.
You light the lantern.  This room appears to be a kitchen.  There's a table with a book in the center.  You
also see an oven, refrigerator and a door leading east.
> Open the oven.
In the oven you see a brown paper bag.
> Take the bag.  Open the bag.  Close the oven.
Inside the bag is a clove of garlic and a cheese sandwich.  The oven door is now closed.

Back then, text adventures were self contained executables on a disk or casette. These days there's usually a data file and an interpreter. The interpreter reads data files and provides the gaming interface. The data files are the actual game itself, similar to the relationship between first person shooters (Section 2.7) and wad files.

The first adventure game was Adventure (actually “ADVENT”, written on a PDP-1 in 1972). You can play Adventure yourself (actually, a descendent); it comes with “bsd games” on most Linux distros. Text adventures became popularized by Scott Adams (Section 11.5) and reached their height of popularity in the late 80's with Infocom (Section 11.4) which are also playable under Linux.

As computer graphics became easier and more powerful, text adventures gave rise to graphic adventures. The death of interactive fiction more or less coincided with the bankruptcy of Infocom.

2.4. Graphical Adventures

Graphical adventures are, at heart, text adventures on steroids. The degree to which they use graphics varies widely. Back in the 80's, they were little more than text adventures which showed a screen of static graphics. When you picked up an item, the background would be redrawn without the item appearing. The canonical example would be the so-called `Hi-Res Adventures' like The Wizard And The Princess. Later on, the sophisticated graphical adventures had your character roaming around the screen, and you could even use a mouse, but the interface remained purely text.

Next there are the `point and click adventures' which basically have no text interface at all, and often have dynamic graphics, like a cat wandering around the room while you're deciding what to do next. In these games, you point at an object (say, a book) and can choose from a pull-down list of functions. Kind of like object oriented adventuring. :) There aren't many graphical adventures written natively for Linux. The only one I can think of is Hopkins FBI (which happens to be my favorite game for Linux).

2.5. Simulation (aka Sims)

Simulations strive to immerse the player behind the controls of something they normally wouldn't have access to. This could be something real like a fighter jet or something imaginary like a mechanized warrior combat unit. In either case, sims strive for realism.

Some sims have little or no strategy. They simply put you in a cockpit to give you the thrill of piloting a plane. Some are considerably complex, and there's often a fine line between sims and strats (Section 2.6). A good example would be Heavy Gear III or Flight Gear. These days sims and strats are nearly indistinguishable, but a long time ago, sims were real time while strats were turn based. This is awkward for modern day use, since a game like Warcraft which everyone knows as a strat, would be a sim by definition.

2.6. Strategy (aka Strats)

Strategy games have their roots in old Avalon type board games like Panzer Leader and old war strategy games published by SSI. Generally, they simulate some kind of scenario. The scenario can be peaceful, like running a successful city (SimCity), illegal drug selling operation (DrugWars) or an all-out war strategy game like Myth II. The types of games usually take a long time to complete and require a lot of brainpower.

Strats can be further divided into two classes: real time and turn based. Real time strats are based on the concept of you-snooze-you-lose. For example, you're managing a city and a fire erupts somewhere. The more time it takes for you mobilize the fire fighters, the more damage the fire does. Turn based strats are more like chess---the computer takes a turn and then the player takes a turn.

2.7. First Person Shooter (aka FPS)

What light through yonder window breaks? It must be the flash of the double barreled shotgun! We have a long and twisted history with FPS games which started when id Software open sourced code for Doom. The code base has forked and merged numerous times. Other previously closed engines opened up, many engines are playable via emulators, many commercial FPS games were released for Linux and there are quite a number of FPS engines which started life as open source projects. Although you may not be able to play your favorite FPS under Linux (Half-Life plays great under winex) Linux definitely has no deficiency here!

First person shooters are characterized by two things. First, you pretty much blow up everything you see. Second, the action takes place in first person. That is, through the eyes of the character who's doing all the shooting. You may even see your hands or weapon at the bottom of the screen. They can be set in fantasy (Hexen), science fiction (Quake II), present day `real world' (Soldier Of Fortune) and many other settings.

Like text adventures, FPS fit the engine/datafile format. The engine refers to the actual game itself (Doom, Quake, Heretic2) and plays out the maps and bad guys outlined by the datafile (doom2.wad, pak0.pak, etc). Many FPS games allow people to write their own non-commercial datafile. There are hundreds, even thousands of non-commercial Doom datafiles that you can download for free off the net. Often, companies release their engines so the open source community so we can hack and improve them. However, the original data files are kept proprietary. To this day, you still have to purchase doom.wad.

2.8. Side Scrollers

Side scrollers are similar to FPS but you view your character as a 2D figure who runs around various screens shooting at things or performing tasks. Examples would be Abuse for Linux and the original Duke Nukem. They don't necessarily have to be violent, like xscavenger, a clone of the old 8-bit game Lode Runner.

2.9. Third Person Shooters

Similar to FPS, but you view your character in third person and in 3D. On modern third person shooters you can usually do some really kick-butt maneuvers like Jackie Chan style back flips and side rolls. The canonical example would be Tomb Raider. On the Linux platform, we have Heretic 2 and Heavy Metal FAKK2.

2.10. Role Playing Game (aka RPG)

Anyone who has played games like Dungeons & Dragons or Call of Cthulhu knows exactly what an RPG is. You play a character, sometimes more than one, characterized by traits (eg strength, dexterity), skills (eg explosives, basket weaving, mechanics) and properties (levels, cash). As you play, the character becomes more powerful and the game adjusts itself accordingly, so instead of fighting orcs, at high levels you start fighting black dragons. The rewards increase correspondingly. At low levels you might get some gold pieces as a reward for winning a battle. At high levels, you might get a magic sword or a kick-butt assault rifle.

RPG's generally have a quest with a well defined ending. In nethack you need to retrieve the amulet of Yendor for your god. In Ultima II, you destroy the evil sorceress Minax. At some point, your character becomes powerful enough that you can `go for it' and try to complete the quest.

While the insanely popular Ultima series, written by Richard Garriot (aka Lord British) for Origin, was not the first RPG, it popularized and propelled the RPG genre into mainstream. Ultima I was released in 1987 and was the game that launched 9 (depending on how you want to count them) very popular sequels, finishing with Ultima IX: Ascension. You can play Ultima VII under Linux with Exult (Section 11.7).

The canonical RPG on Linux is Rogue (the ncurses library started life as a screen handling routine for Rogue!) and it has infinite variants like Zangband and Nethack (which has many variants itself). Some RPG's are quite complicated and great feats of programming. There seems to be a deficiency of commercial RPGs for Linux. Not counting the rogue variants, there's also a deficiency of open source RPGs too.

3.1. What is Glide2?

Glide2 is a low level graphics API and driver that accesses 3D hardware accelerated functions on 3dfx's Voodoo I, II and III cards, under XFree86 3.x.

A program can only use the special hardware accelerated features of these cards by using the Glide2 library in one of two ways:

• directly written using Glide2 (Myth II, Descent III)

• indirectly using Mesa built with a Glide2 backend to simulate OpenGL (Rune, Unreal Tournament)

3dfx opened up the specifications and source code to the open source community. This allowed Daryll Strauss to port Glide2 to Linux which enabled XFree86 3.x users to use Voodoo I, II and III cards under Linux.

Since Glide2 accesses the video card directly, Glide2 applications will either need to be run by root or be setuid root. A way around this was to create the kernel 3dfx module. This module (and its device file /dev/3dfx) allows Glide2 graphical hardware acceleration for non-root users of non-setuid applications.

Unfortunately, Glide2 is also a dead issue. It's only used for Voodoo I, II, III boards (which are becoming outdated), under XFree86 3.x (most people use XFree86 4.x). And since 3dfx is now a defunct company, it's a sure bet that no more work will be done on Glide2 and no more games will be written using Glide2.

3.2. What is Glide3?

Unlike Glide2, Glide3 is not an API used for game programming. It exists only to support DRI on Voodoo III, IV and V boards under XFree86 4.x. None of the games which use Glide2 will work with Glide3. This shouldn't be a surprise since Glide2 and Glide3 support different video cards and different versions of XFree86. The only video card that can use both Glide2 (under XFree86 3.x) and Glide3 (under XFree86 4.x) is the Voodoo III. It's reported that a Voodoo III using Glide2 will outperform a Voodoo III using Glide3.

When you use a Voodoo III, IV or V under XFree86 4.x, you want to use a version of Mesa (see Section 3.4) which was compiled to use Glide3 as a backend to ensure hardware accelerated OpenGL on your system.

3.3. What is OpenGL?

OpenGL is a high level graphics programming API originally developed by SGI, and it became an industry standard for 2D and 3D graphics programming. It's defined and maintained by the Architectural Revision Board (ARB), an organization which include representatives from SGI, IBM, DEC, and Microsoft. OpenGL provides a powerful, complete and generic feature set for 2D and 3D graphics operations.

There are 3 canonical parts to OpenGL:

• GL: The OpenGL core calls

• GLU: The utility calls

• GLUT: System independent window event handling (mouse events, keyboard events, etc.).

OpenGL is not only an API, it's also an implementation, written by SGI. The implementation tries to use hardware acceleration for various graphics operations whenever available, which depends on what videocard you have in you computer. If hardware acceleration is not possible for a specific task, OpenGL falls back on software rendering. This means that when you get OpenGL from SGI, if you want any kind of hardware acceleration at all, it must be OpenGL written and compiled specifically for some graphics card. Otherwise, all you'll get is software rendering. The same thing is true for OpenGL clones, like Mesa.

OpenGL is the open source equivalent to Direct3D, a component of DirectX (Section 3.14). The important difference being that since OpenGL is open (and DirectX is closed), games written in OpenGL are much easier to port to and co-develop on Linux than games written using DirectX.

3.4. What is Mesa?

Mesa <http://www.mesa3d.org> is a free implementation of the OpenGL API, designed and written by Brian Paul. While it's not officially certified (that would take more money than an open source project has), it's an almost fully compliant OpenGL implementation conforming to the ARB specifications. It's reported that Mesa is even faster than SGI's own OpenGL implementation.

Just like OpenGL, Mesa makes use of hardware acceleration whenever possible. When a particular graphics task isn't able to be hardware accelerated by the video card, it's software rendered; the task is done by your computer's CPU instead. This means that there are different builds of Mesa depending on what kind of video card you have. Each build uses a different library as a backend renderer. For example, if you have a Voodoo I, II or III card under XFree86 3.x, you'd use mesa+glide2 (written by David Bucciarelli) which is the Mesa implementation of OpenGL that uses Glide2 as a backend to render for graphical operations.

3.5. What is DRI?

Graphics rendering has 3 players: the client application (like Quake 3), the X server and the hardware (the graphics card). Previously, client applications were prohibited from writing directly to hardware, and there was a good reason for this. A program that is allowed to directly write to hardware can crash the system in any number of ways. Rather than trusting programmers to write totally bug free, cooperative programs that access hardware, Linux simply disallowed it. However, that changed under X 4.x with DRI (Direct Rendering Infrastructure <http://www.dri.sourceforge.net>. DRI allows X clients to write 3D rendering information directly to the video card in a safe and cooperative manner.

DRI gets the X server out of the way so the 3D driver (Mesa or OpenGL) can talk directly to the hardware. This speeds things up. The 3D rendering information doesn't even have to be hardware accelerated. On a technical note, this has a number of virtues.

• Vertex data doesn't have to be encoded/decoded via GLX.

• Graphics data isn't sent over a socket to the X server.

• On uni-processor machines the CPU doesn't have to change context between XFree86 and its client to render the graphics.

3.6. What is GLX?

GLX is the X extension used by OpenGL programs, it is the glue between the platform independent OpenGL and platform dependent X.

3.7. What is Utah GLX?

Utah-GLX is the precursor to DRI. It makes some different design decisions regarding separation of data and methods of accessing the video card like relying on root access rather than creating the kernel infrastructure for secure access. It provides support for a few cards which are not well supported by DRI like the ATI Rage Pro family, S3 Virge (although anyone using this for gaming is, well, nuts), and an open source TNT/TNT2 driver (which is very incomplete). The TNT/TNT2 driver is based on reverse-engineering of the obfuscated source code release of the X 3.3 drivers by nVidia. However, they're really incomplete, and effectively, unusable.

3.8. What is xlib?

Every once in awhile you'll see some sicko (said with respect) write a game in xlib. It is a set of C libraries which comprise the lowest level programming interface for XFree86. Any graphics programming in X ultimately makes use of the xlib library.

It's not an understatement to say that xlib is long winded, arcane and complicated. Because of this, there are lots of libraries like SDL (Section 3.10) for 2D graphics, OpenGL (Section 3.3) for 3D graphics and widget sets (Section 3.9) for widgets within windows which hide the details of different aspects of xlib programming.

While some games are written in xlib, like the Doom Editor Yadex, xlib itself is not a serious game writing library. Most games don't need the low-level interface that xlib provides. In addition, by using the higher level libraries, a game writer can develop his game on multiple platforms, even ones that don't use XFree86.

3.9. What is a widget set?

Widgets are objects that make up a GUI application's interface. They include things like text entry boxes, pulldown menus, slider bars, radio buttons and much more. A widget set is a collection of related widgets that are designed to have a common interface and a consistant "feel". Gtk is the canonical widget set on Linux, but there are many others like fltk (a small C++ widget set), Xaw, Qt (the widget set of KDE), and Motif (the widget set used by Netscape). Motif used to be the king of widget sets in the Unix world, but it was very expensive to license. The Open Group finally opened up Motif's license for open source operating systems, but it was too little too late. There are many completely open source widget sets which are more complete and much nicer looking than Motif, including Lesstif, a totally free Motif clone.

3.10. What is SDL (Simple DirectMedia Layer)?

SDL <http://www.libsdl.org> is a library by Sam Lantiga (graduate of UCD, yeah!). It's actually a meta-library, meaning that not only is it a graphics library which hides the details of xlib programming, it provides an easy interface for sound, music and event handling. It's LGPL'd and provides joystick and OpenGL support as well. Unlike xlib (Section 3.8), SDL is very suited for game programming.

The most striking part of SDL is that it's a cross platform library. Except for a few details, a program written in SDL will compile under Linux, MS Windows, BeOS, MacOS, MacOS X, Solaris, IRIX, FreeBSD, QNX and OSF. There are SDL extentions written by various people to do things like handle any graphics format you care to mention, play mpegs, display truetype fonts, sprite handling and just about everything under the sun. SDL is an example of what all graphics libraries should strive for.

Sam had an ulterior motive for writing such a cool library. He was the lead programmer for Loki Software (he now codes for Blizzard Software), which used SDL in all of its games except for Quake3.

3.11. What is GGI?

GGI <http://www.ggi-project.org> is a project which aims to implement a graphics abstraction layer in lower level code, put graphics hardware support into a common codebase, and bring higher stability and portability to graphics applications. LibGGI applications run on SVGAlib, fb, and X servers among others. Judging from their screenshots, this is quite a powerful library.

Applications that use LibGGI directly include Heroes, Ultrapoint, Quake, and Berlin. Most applications that use SVGALib can be run on X or any other LibGGI backend by using a wrapper library which re-implements SVGALib (Section 3.12) using LibGGI. SDL (Section 3.10) and clanlib (Section 3.15) applications can display on LibGGI but often the native drivers for these libraries are faster, however it's a good way to get SDL, clanlib, and SVGALib applications to run where they would not before.

GGI has a sister project, KGI, which is developing a kernel-level alternative to systems like the linux framebuffer and the DRI. This project is much less far along than LibGGI itself, but promises to combine DRI-level speeds and the stability and security UNIX users expect.

3.12. What is SVGAlib? Frame buffer? Console?

The console is the dark non-graphical screen you look at when your computer first boots up (and you don't have xdm or gdm running). This is opposed to the X environment which has all sorts of GUI things like xterms. It's a common misconception that X means graphics and console means no graphics. There are certainly graphics on the console—we will discuss the two most common ways to achieve this.

SVGAlib is a graphics library that lets you draw graphics on the console. There are many graphical applications and games that use SVGAlib like zgv (a console graphical image viewer), prboom and hhexen. I happen to be a fan of this library and of graphical console games in general; they are extremely fast, fullscreen and compelling. There are three downsides to SVGAlib. First, SVGAlib executables need to be run by root or be setuid root, however, the library releases root status immediately after the executable begins to run. Secondly, SVGAlib is video card dependent–if your video card isn't supported by SVGAlib, you're out of luck. Third, SVGAlib is Linux only. Games written in SVGAlib will only work on Linux.

Frame buffers are consoles implemented by a graphics mode rather than a BIOS text mode. Why simulate text mode in a graphical environment? This allows us to run graphical things in console, like allowing us to choose any font we want the console to display (which is normally set by BIOS). There's a good Frame Buffer HOWTO available from LDP. Graphical console games written using the frame buffer suffer from the same deficiencies of the SVGA library: not all hardware is supported and the code will only run on Linux.

3.13. What is OpenAL?

OpenAL <http://www.openal.org> aims to be for sound what OpenGL is for graphics. Jointly developed by Loki Software and Creative Labs, it sets out to be a vendor neutral and cross platform API for audio. It is licensed LGPL and the specs can be had for free from the OpenAL website. OpenAL is fully functional, but now that Loki Software is no more its future development is questionable.

3.14. What is DirectX?

DirectX is a collection of proprietary multimedia API's, first developed by Microsoft in 1995, for its various Windows OS's. It's a mistake to say something like "DirectX is like OpenGL" or "DirectX is like SDL", as is commonly said in DirectX tutorials. Multimedia API's are more centralized on Windows than they are on Linux. A more accurate statement would be something like "DirectX is like DRI, OpenGL and SDL combined". As of Feb 2002, the most recent version of DirectX is 8.1. The components of DirectX are:

DirectX is "kind of" supported by winex (Section 10.4.3), poorly supported by wine (Section 10.4.1), barely supported by vmware (Section 10.4.5) and unsupported by Win4Lin (Section 10.4.4).

One comment about portability. Each component of DirectX has multiple corresponding library on Linux. Moreover, a game writer who uses libraries like OpenGL, GGI or SDL will write a game which will trivially compile on Windows, Linux and a multitude of other OS's. Yet game companies persist using DirectX and therefore limit their audience to Windows users only. If you're a game writer, please consider using cross platform libraries and stay away from DirectX.

A company named realtechVR started an open source project, DirectX Port, <http://www.v3x.net/directx> which, like wine, provides a Direct3D emulation layer that implements Direct3D calls. The project was focused on the BeOS platform, but is now focused on MacOS and Linux. You can get the latest cvs from their sourceforge page at <http://sourceforge.net/projects/dxglwrap>.

3.15. Clanlib

ClanLib is a medium level development kit. At its lowest level, it provides a platform independent (as much as that is possible in C++) way of dealing with display, sound, input, networking, files, threading and such. ClanLib builds a generic game development framework, giving you easy handling of resources, network object replication, graphical user interfaces (GUI) with theme support, game scripting and more.

4.1. Textures

A rendered scene is basically made up of polygons and lines. A texture is a 2D image (usually a bitmap) covering the polygons of a 3D world. Think of it as a coat of paint for the polygons.

4.2. T&L: Transform and Lighting

The T&L is the process of translating all the 3D world information (position, distance, and light sources) into the 2D image that is actually displayed on screen.

4.3. AA: Anti Aliasing

Anti aliasing is the smoothing of jagged edges along a rendered curve or polygon. Pixels are rectangular objects, so drawing an angled line or curve with them results in a 'stair step' effect, also called the 'jaggies'. This is when pixels make, what should be a smooth curve or line, jagged. AA uses CPU intensive filtering to smooth out these jagged edges. This improves a game's visuals, but can also dramatically degrade performance.

AA is used in a number of situations. For instance, when you magnify a picture, you'll notice lines that were once smooth become jagged (try it with The Gimp). Font rendering is another big application for AA.

AA can be done either by the application itself (as with The Gimp or the XFree86 font system) or by hardware, if your video card supports it. Since AA is CPU intensive, it's more desirable to perform it in hardware, but if we're talking about semi-static applications, like The Gimp, this really isn't an issue. For dynamic situations, like games, doing AA in hardware can be crucial.

4.4. FSAA: Full Screen Anti-Aliasing

FSAA usually involves drawing a magnified version of the entire screen in a separate framebuffer, performing AA on the entire image and rescaling it back to the normal resolution. As you can imagine, this is extremely CPU intensive. You will never see non hardware accelerated FSAA.

4.5. Mip Mapping

Mip mapping is a technique where several scaled copies of the same texture are stored in the video card memory to represent the texture at different distances. When the texture is far away a smaller version of the texture (mip map) is used. When the texture is near, a bigger one is used. Mip mapping can be used regardless of filtering method (Section 4.6). Mip mapping reduces memory bandwidth requirements since the images are in hardware, but it also offers better quality in the rendered image.

4.6. Texture Filtering

Texture filtering is the fundamental feature required to present sweet 3D graphics. It's used for a number of purposes, like making adjacent textures blend smoothly and making textures viewed from an angle (think of looking at a billboard from an extreme angle) look realistic. There are several common texture filtering techniques including point-sampling, bilinear, trilinear and anisotropic filtering.

When I talk about 'performance hits', keep in mind that the performance hit depends on what resolution you're running at. For instance, at a low resolution you may get only a very slight hit by using trilinear filtering instead of bilinear filtering. But at high resolutions, the performance hit may be enormous. Also, I'm not aware of any card that uses anisotropic texture filtering. TNT drivers claim they do, but I've read that these drivers still use trilinear filtering when actually rendering an image to the screen.

4.7. Z Buffering

A Z buffer is a portion of RAM which represents the distance between the viewer (you) and each pixel of an object. Many modern 3D accelerated cards have a Z buffer in their video RAM, which speeds things up considerably, but Z buffering can also be done by the application's rendering engine. However, this sort of thing clearly should be done in hardware wherever possible.

Every object has a stacking order, like a deck of cards. When objects are rendered into a 2D frame buffer, the rendering engine removes hidden surfaces by using the Z buffer. There are two approaches to this. Dumb engines draw far objects first and close objects last, obscuring objects below them in the Z buffer. Smart engines calculate what portions of objects will be obscured by objects above them and simply not render the portions that you won't see anyhow. For complicated textures this is a huge savings in processor work.

5.1. Getting information about your X system

Whether you're trying to diagnose an X problem or requesting help from a mailing list or Usenet newsgroup, you'll want to have as much information available as possible. These are a set of tools you can use to obtain that information.

    X -probeonly 2> X.out
					

    (--) probed              (**) from config file    (==) default setting
    (++) from command line   (!!) notice              (II) informational
    (WW) warning             (EE) error               (??) unknown.
					

    (**) TDFX(0): Depth 16, (--) framebuffer bpp 16
					

    (--) Chipset 3dfx Voodoo5 found
    (--) TDFX(0): VideoRAM: 32768 kByte Mapping 65536 kByte
					

5.2. Playing Games In X Without a Window Manager

6.1. Memory Type Register Ranges

Starting with Pentium class processors and including Athlon, K6-2 and other CPUs, there are Memory Type Register Ranges (MTRR) which control how the processor accesses ranges of memory locations. Basically, it turns many smaller separate writes to the video card into a single write (a burst). This increases efficiency in writing to the video card and can speed up your graphics by 250% or more.

See /usr/src/linux/Documentation/mtrr.txt for details. Note that since this file was written, XFree86 has been patched to automatically detect your video RAM base address and size and set up the MTRRs.

6.2. Milking performance from your system for all it's worth

• If for some reason you're using X 3.3, follow the instructions given by mtrr.txt (see section 5.1) to set up your MTRRs. X 4.0 does this automatically for you.

• Don't run a window manager (wm). Some wm's like twm don't take up much CPU cycles, but still rob you of performance. Some window managers like enlightenment will definitely produce a noticeable slow down. To run a game without a wm, you modify .xinitrc in your home directory. Here is what my .xinitrc looks like:

  #quake3 +set r_gldriver libGR.so.1 #/usr/local/games/SinDemo/Sin #exec ut #lsdldoom -server 2 #exec tribes2 exec /usr/bin/enlightenment

  This file tells X what client to run upon starting. Usually this is your wm, and/or a desktop manager (GNOME or KDE). Comment out the lines containing a wm and desktop manager with a pound sign (#) and place your game on a new line with any command line arguments you want to pass. If the game is not located in your $PATH, give its full path name. Note that this is for people who use `startx' to start X.

  I never use things like gdm or run-level 5 (so I'm not positive here), but I suspect that if you do, you'll need to do things a bit differently. My best guess is to go to single user mode (run-level 1) by:

  # telinit 1

  then edit .xinitrc, then go back to run-level 5 by

  # telinit 5

  Then when you stop playing, go to run-level 1, modify .xinitrc then go back to run-level 5. I don't use this stuff, so I'm not sure, but you may need to kill gdm. I'd appreciate some feedback on this.

  Kill all not-essential processes. Of course you'll have to do this as root. A better way to do this than typing "ps ax", getting ntpd's pid, and sending it a SIGKILL (with kill -9) is to make use of pidof:

  # kill -9 `pidof ntpd`

  However, an even better alternative is to use the startup scripts on your system. On Debian, the startup scripts for run-level 2 are located in /etc/rc2.d/. You can kill a service in an orderly manner by sending its startup scrip the `stop' command:

  # cd /etc/rc2.d # ./ntpd stop

  Another (radical) option is to simply put yourself in single-user mode with

  # telinit 1

  This will even get rid of getty; your system will be running nothing which is absolutely crucial to its operation. You'll have something like 10 processes running. The downside is that you'll have to play the game as root. But your process table will be a ghost town, and all that extra CPU will go straight to your game.

6.3. About libraries on Linux

A common problem you'll see in gaming is a library file not being found. They're kind of mysterious and have funny names, so we'll go over libraries on Linux for a bit. There are two types of libraries, static and dynamic. When you compile a program, by default, gcc uses dynamic libraries, but you can make gcc use static libraries instead by using the -static switch. Unless you plan on compiling your games from source code, you'll mainly be interested in dynamic libraries.

    /usr/lib/libSDL.so
    /lib/libm.so.3
			

    /usr/lib/libSDL.a
    /usr/lib/libm.a
			

    % nm /usr/lib/libm.a
    ...
    e_atan2.o:
    00000000 T __ieee754_atan2
    
    e_atanh.o:
    00000000 T __ieee754_atanh
    00000000 r half
    00000010 r limit
    00000018 r ln2_2
    ...
			

7.1. RTFM!

Read the friendly manual. The `manual' can take on a few forms. For open source games there's the readme files that come with the game. Commercial games will have a printed manual and maybe some readme files on the CD the game came on. Don't forget to browse the CD your game came on for helpful tips and advice.

Don't forget the game's website. The game's author has probably seen people with your exact same problem many times over and might put information specific to that game on the website. A prime example of this is Loki Software's online FAQs located at http://faqs.lokigames.com.

7.2. Look For Updates and Patches

If you're playing an open source game that you compiled, make sure you have the newest version by checking the game's website. If your game came from a distro make sure there's not an update rpm/deb for the game.

Commercial game companies like Loki release patches for their games. Often a game will have MANY patches (Myth2) and some games are unplayable without them (Heretic2). Check the game's website for patches whether you have a problem running the game or not; there may be an update for a security problem that you may not even be aware of.

By the way, Loki now has a utility that searches for Loki Software on your hard drive and automatically updates them. Check out http://updates.lokigames.com.

7.3. Newsgroups

If you don't know what netnews (Usenet) is, then this is definitely worth 30 minutes of your time to learn about. Install a newsreader. I prefer console tools more, so I use tin, but slrn is also popular. Netscape has a nice graphical "point and click" newsreader too.

For instance, I can browse Loki Software's news server with tin -g news.lokigames.com. You can also specify which news server to use using the $NNTP environment variable or with the file /etc/nntpserver.

7.4. Google Group Search

Every post made to Usenet gets archived at Google's database at http://groups.google.com. This archive used to be at http://www.deja.com, but was bought by Google. Many people still know the archive as "deja".

It's almost certain that whatever problem you have with Linux, gaming related or not, has already been asked about and answered on Usenet. Not once, not twice, but many times over. If you don't understand the first response you see (or if it doesn't work), then try one of the other many replies. If the page is not in a language you can understand, there are many translation sites which will convert the text into whatever language you like, including http://www.freetranslation.com and http://translation.lycos.com. My web browser of choice, Opera (available at http://www.opera.com allows you to use the right mouse button to select a portion of text and left click the selection to translate it into another language. Very useful when a Google group search yields a page in German which looks useful and my girlfriend (who reads German well) isn't around.

The Google group search has a basic and advanced search page. Don't bother with the simple search. The advanced search is at http://groups.google.com/advanced_group_search

It's easy to use. For example, if my problem was that Quake III crashed everytime Lucy jumps, I would enter "linux quake3 crash lucy jumps" in the "Find messages with all of the words" textbox.

There are fields for which newsgroup you want to narrow your search to. Take the time to read and understand what each field means. I promise you. You won't be disappointed with this service. Use it, and you'll be a much happier person. Do note that they don't archive private newsgroups, like Loki Software's news server. However, so many people use Usenet, it almost doesn't matter.

7.5. Debugging: call traces and core files

This is generally not something you'll do for commercial games. For open source games, you can help the author by giving a corefile or stack trace. Very quickly, a core file (aka core dump) is a file that holds the "state" of the program at the moment it crashes. It holds valuable clues for the programmer to the nature of the crash -- what caused it and what the program was doing when it happened. If you want to learn more about core files, I have a great gdb tutorial at http://www.dirac.org/linux.

At the *very* least, the author will be interested in the call stack when the game crashed. Here is how you can get the call stack at barf-time:

Sometimes distros set up their OS so that core files (which are mainly useful to programmers) aren't generated. The first step is to make your system allow unlimited coresizes:

    ulimit -c unlimited
			

You will now have to recompile the program and pass the -g option to gcc (explaining this is beyond the scope of this document). Now, run the game and do whatever you did to crash the program and dump a core again. Run the debugger with the core file as the 2nd argument:

    $ gdb CoolGameExecutable core
			

And at the (gdb) prompt, type "backtrace". You'll see something like:

    #0 printf (format=0x80484a4 "z is %d.\n") at printf.c:30
    #1 0x8048431 in display (z=5) at try1.c:11
    #2 0x8048406 in main () at try1.c:6
			

It may be quite long, but use your mouse to cut and paste this information into a file. Email the author and tell him:

1. The game's name

2. Any error message that appears on the screen when the game crashes.

3. What causes the crash and whether it's a repeatable crash or not.

4. The call stack

If you have good bandwidth, ask the author if he would like the core file that his program dumped. If he says yes, then send it. Remember to ask first, because core files can get very, very big.

7.6. Saved Games

If your game allows for saved games, then sending the author a copy of the saved game is useful because it helps the tech reproduce whatever is going wrong. For commercial games, this option is more fruitful than sending a core file or call stack since commercial games can't be recompiled to include debugging information. You should definitely ask before sending a save game file because they tend to get long, but a company like Loki Software has lots of bandwidth. Mike Phillips (formerly of Loki Software) mentioned that sending in saved games to Loki is definitely a good thing.

Needless to say, this only applies if your game crashes reproducably at a certain point. If the game segfaults every time you run it, or is incredibly slow, a saved game file won't be of much help.

7.7. What to do when a file or library isn't being found (better living through strace)

Sometimes you'll see error messages that indicate a file wasn't found. The file could be a library:

    % ./exult 
    ./exult: error while loading shared libraries: libSDL-1.2.so.0: cannot load shared object
    file: No such file or directory
			

or it could be some kind of data file, like a wad or map file:

    % qf-client-sdl  
    IP address 192.168.0.2:27001 UDP Initialized Error: W_LoadWadFile: couldn't load gfx.wad
			

Suppose gfx.wad is already on my system, but couldn't be found because it isn't in the right directory. Then where IS the right directory? Wouldn't it be helpful to know where these programs looked for the missing files?

This is where strace shines. strace tells you what system calls are being made, with what arguments, and what their return values are. In my `Kernel Module Programming Guide' (due to be released to LDP soon), I outline everything you may want to know about strace. But here's a brief outline using the canonical example of what strace looks like. Give the command:

    strace -o ./LS_LOG /bin/ls
			

The -o option sends strace's output to a file; here, LS_LOG. The last argument to strace is the program we're inspecting, here, "ls". Look at the contents of LS_LOG. Pretty impressive, eh? Here is a typical line:

    open(".", O_RDONLY|O_NONBLOCK|0x18000)  = 4
			

We used the open() system call to open "." with various arguments, and "4" is the return value of the call. What does this have to do with files not being found?

Suppose I want to watch the StateOfMind demo because I can't ever seem to get enough of it. One day I try to run it and something bad happens:

    % ./mind.i86_linux.glibc2.1 
    Loading & massaging...
    Error:Can't open data file 'mind.dat'.
			

Let's use strace to find out where the program was looking for the data file.

    strace ./mind.i86_linux.glibc2.1 2> ./StateOfMind_LOG
			

Pulling out vim and searching for all occurrences of mind.dat, I find the following lines:

    open("/usr/share/mind.dat",O_RDONLY) = -1 ENOENT (No such file)
    write(2, "Error:", 6Error:)   = 6
    write(2, "Can\'t open data file \'mind.dat\'."..., ) = 33
			

It was looking for mind.dat in only one directory. Clearly, mind.dat isn't in /usr/share. Now we can try to locate mind.dat and move it into /usr/share, or better, create a symbolic link.

This method works for libraries too. Suppose the library libmp3.so.2 is in /usr/local/include but your new game "Kill-Metallica" can't find it. You can use strace to determine where Kill-Metallica was looking for the library and make a symlink from /usr/local/include/libmp3.so.2 to wherever Kill-Metallica was looking for the library file.

strace is a very powerful utility. When diagnosing why things aren't being found, it's your best ally, and is even faster than looking at source code. As a last note, you can't look up information in source code of commercial games from Lokisoft or Tribsoft. But you can still use strace with them!

7.8. Hosed consoles

Sometimes a game will exit abnormally and your console will get `hosed'. There are a few definitions of a hosed console. The text characters could look like gibberish. Your normally nice black screen could look like a quasi-graphics screen. When you press ENTER, a newline doesn't get echo'ed to the screen. Sometimes, certain keys of the keyboard won't respond. Logging out and back in won't work, but there are a few things that might:

• At the prompt, type "reset". This should clear up many problems, including consoles hosed by an SVGAlib or ncurses based game.

• Try running the game again and normally. Once I had to kill Quake III in a hurry, so I gave it the 3 fingered salute. The console was hosed with a quasi-graphics screen. Running Quake III and quitting normally fixed the problem.

• The commands deallocvt and openvt will work for most of the other problems you'll have. deallocvt N kills terminal N entirely, so that Alt-FN doesn't even work anymore. openvt -c N starts it back up.

• If certain keys on your keyboard don't work, be creative. If you want to reboot but the `o' key doesn't work, try using halt. One method I've come up with is typing a command at the prompt and using characters on the screen with mouse cut/paste. For example, you can type "ps ax", and you're sure to have an `h', `a', `l' and a `t' somewhere on the screen. You can use the mouse to cut and paste the word "halt".

• The most regrettable option is a reboot. If you can, an orderly shutdown is preferable; use "halt" or "shutdown". If you can't, ssh in from a another machine. That sometimes works when your console is very badly hosed. In the worst case scenario, hit the reset or power switch.

Note that if you use a journalling filesystem like ext3, reiserfs or xfs, hitting the power switch isn't all that bad. You're still supposed to shutdown in an orderly manner, but the filesystem integrity will be maintained. You won't see an fsck for the partitions that use the journalling filesystem.

7.9. Locked System

When a computer "locks", also called "hung", the keyboard and mouse become completely unresponsive. This is a direct consequence of a bug in the Linux kernel. While Linux is known for stability, these things do happen, especiallly for gaming which entails highly synchronized hardware events which occur very fast, even to a computer. When a computer locks, it can be a "hard lock", meaning the kernel has completely stopped functioning. This often indicates misbehaving or faulty hardware. There's no recovery from this kind of lock other than pressing the reset or power button. The lock can also be a "soft lock", meaning that the kernel is still functioning in some capacity. It's possible to recover from this gracefully.

• The first thing you should try is to hit control-alt-backspace which kills X. If you gain control of your system, the kernel wasn't really locked in the first place. If this didn't work after a few seconds, you'll definitely want to reboot the system using the following instructions.

• Use control-alt-delete to reboot the system. You'll know this worked if you hear the computer beep after a few seconds (this is BIOS saying "I'm OK" during a power on cycle).

• Log into another system and ssh into the hung system. If you can ssh in, reboot or halt the system.

• If you can't ssh into the system, you'll need to use the "magic SysRq key" which is documented in /usr/src/linux/Documentation/sysrq.txt. Here's a summary for the x86 architecture (see the documentation for other architectures). Note if your keyboard doesn't have a SysRq key, use the PrintScreen key:

  1. Hit alt-SysRq-s. This will attempt to sync your mounted filesystems so that changes to files get flushed to disk. You may hear disk activity. If you're looking at a console, the system should print the devices which were flushed.

  2. A few seconds later, hit alt-SysRq-u. This will attempt to remount all your mounted filesystems as read-only). You should hear disk activity. If you're looking at a console, the system will print the devices which were remounted.

  3. A few seconds later, use alt-SysRq-b to reboot the system.

  4. You can hit alt-SysRq-h for a very terse help screen.

To use the magic SysRq key, your kernel needs to have been compiled with magic SysRq support. You'll find this option under "Kernel Hacking | Kernel Debugging | Magic SysRq key" in whatever kernel config menu you like to use. If the magic SysRq key sequence doesn't shut your system down gracefully, your kernel has crashed hard and you'll need to use the reset or power button to recover.

8.1. Which video card is the best?

If you're using Linux, you must be smart enough to know that there isn't a plain answer to this question. There seem to be 3 choices for hardware accelerated 3D these days:

1. 3dfx: Voodoo cards

2. Nvidia: GeForce

3. ATI: Radeon

According to Tom's Hardware and Anadtech, the Radeon is king when playing at very high resolution (as in 1600x1200), at 32bpp, in Windows. Otherwise the GeForce is king. There are two problems with this. We don't normally play at 1600x1200/32bb, and we don't play on Windows (at least I don't).

There aren't many recent video card benchmarks out for Linux. The most recent one I've seen is from March 2001 at http://www.linuxhardware.org/features/01/03/19/0357219.shtml. Considering the dearth of benchmarks out there, this needs to be taken as a canonical benchmark, so I simply quote their conclusion:

At this point the performance numbers tell a pretty simple story, if it's raw speed you are looking for, the GeForce 2 is your choice. There is very little performance drawback to running your favorite games in Linux instead of Windows with this card. It provides a truly impressive performace across the board. The Radeon's performance will almost definitely improve as the DRI drivers mature, but for now, especially for the impatient, it is simply not a good choice for the hard core 3d gamer.

If, however, you are a graphics designer, and want a card with impeccable 2d image quality, with 3d graphics only a secondary priority, the Radeon is your best bet. The DRI drivers, even in their current state, are quite usable. For 2d only users, XFree86 4.0.2 provides production quality 2d drivers. The GeForce thoroughly trounced the Radeon in the Xmark performance test, so if you aren't running at a ultra high resolution, or aren't that picky, the GeForce is once again a better pick.

Now for my own input. The Radeon is a pretty amazing card. It's what I use, and I have yet to see a game that needs more power than the Radeon is able to provide. However, the OpenGL renderer for the Radeon is buggy, although the only games I've seen that suffer greatly are Loki Software's Heavy Metal and Soldier Of Fortune. Hopefully the people doing Mesa for the Radeon will fix this very soon since the Radeon is the best option for people who don't want to rely on the closed source, proprietary GeForce. As of June 2002, SVGAlib support Radeon cards is shaky. Developers have reported that SVGAlib works on the Radeon 7500, Radeon QD (ddr 64MB model) but has problems on the Radeon VE.

Now about the Voodoo cards. Unfortunately, 3dfx was bought out by nVidia, so these cards are a dead end market. If you're out to play the bleeding edge games like Rune or Tribes2, you'll want the Voodoo 3, 4 or 5. Preferably the 4 or 5. I think the Voodoo 5 is basically a Voodoo 4 with a second processer. However, this processor is not utilized by the Linux driver, and rumor says that the Linux 3dfx driver will never support it. So as far as Linux is concerned, the Voodoo 4 and 5 are the same card. All the drivers, Glide2 library and OpenGL renderers for the Voodoo cards were open sourced by 3dfx before they when under. It is an embarrasment to the Linux and open source community in general that this company failed. SVGAlib officially supports only the Voodoo Banshee and the Voodoo III, but from first hand experience, I've seen SVGAlib programs run on all the Voodoo cards.

8.2. Which sound card is best?

Now that Linux is beginning to mature, this question isn't as important as it used to be. Once upon a time, soundcards without onboard MIDI chips (most PCI sound cards) didn't do MIDI. This was mostly a problem for things like xdoom or lxdoom using musserv. These days we have MIDI emulators like Timidity and libraries like SDL which don't require hardware MIDI support. Frankly, I've had many cards and I can't tell the difference between any of them for gaming. If you want to do things like convert a record LP to digital format, then your choice of a soundcard with a professional grade A/D converter is absolutely crucial. For this HOWTO, we'll assume that you're more of a gamer than a studio recording engineer.

Your decision should be based on what will be the easiest to configure. If you already have a card and it works well, that's good enough. If you're in the market to buy a sound card, get something that will take you a second to configure. PCI cards are much easier to deal with than ISA since you don't need to tell their drivers about which system resources (IRQ, DMA, I/O addresses) to use. Some ISA cards ARE plug-n-play, like the Creative AWE-64, and the Linux kernel has come a long way in auto configuring them.

My personal recommendation is any card which has the es1370 or es1371 chip, which uses the es1370 and es1371 sound drivers on Linux. These cards include the older Ensoniq es1370 and newer Creative PCI-128. These cards are extremely cheap and trivial to get working under Linux.

I used to be quite a big fan of the Creative Soundblaster AWE 32, AWE 64 and AWE 64 gold soundcards. They are ISA, but are plug-n-play. A couple of issues to note. First, the Creative AWE HOWTO is very out of date. Second, AFAIK, Creative never released a Linux driver that uses the AWE 64's extra 32 voices (and they never released programming information for it either). So to a Linux users, the AWE 64 and 32 are nearly identical sound cards. If anyone has more information about the differences that a Linux user would see between the AWE 64 and 32, I'd like to hear from you.

The Creative Soundblaster Live! is an extremely popular PCI sound card these days. I've never owned one, so I cannot comment here. However, there have been numerous reports about serious problems with the Live! and AMD motherboards that use the 686b southbridge. A google search should turn up alot of information on this problem.

A more relevent issue is speakers, but even here the difference isn't huge. I've had expensive Altec Lansing speakers perform only slightly better than el-cheapo speakers. You get what you pay for with speakers, but don't expect a huge difference. You'll want to get something with a separate sub-woofer; this does make a difference at a cost of extra power and connector wires.

9.1. Hardware Acceleration Problems

XFree86 4.x provides a more centralized and self-contained approach to video. Much of the funkyness like kernel modules for non-root access of video boards is, thankfully, gone.

9.2. Hardware acceleration works only for the root user

    Section "DRI"
        Mode 0666
    EndSection
					

9.3. Why isn't my sound working?

First of all, it's probably not the game, it's probably your setup. AFAIK, there are 3 options to getting a sound card configured under Linux: the free OSS sound drivers that come with the Linux kernel, the Alsa drivers and the commercial OSS sound drivers. Personally, I prefer the free OSS drivers, but many people swear by Alsa. The commercial OSS drivers are good when you're having trouble getting your sound card to work by free methods. Don't discount them; they're very cheap (like 10 or 20 bucks), support bleeding edge sound cards and take a lot of guesswork out of the configuring process.

There are 5 things that can go wrong with your sound system:

1. Shared interrupt

2. Misconfigured driver

3. Something's already accessing the sound card

4. You're using the wrong driver

5. A permissions problem

    $ cat /proc/interrupts
               CPU0       CPU1
      0:   24185341          0          XT-PIC  timer
      1:     224714          0          XT-PIC  keyboard
      2:          0          0          XT-PIC  cascade
      5:    2478476          0          XT-PIC  soundblaster
      5:     325924          0          XT-PIC  eth0
     11:     131326          0          XT-PIC  aic7xxx
     12:    2457456          0          XT-PIC  PS/2 Mouse
     14:     556955          0          XT-PIC  ide0
    NMI:          0          0
    LOC:   24186046   24186026
    ERR:       1353
					

    # lsof /dev/dsp
    COMMAND    PID USER   FD   TYPE DEVICE SIZE   NODE NAME
    mp3blaste 1108    p    6w   CHR   14,3      662302 /dev/dsp
					

    # fuser -vk /dev/dsp
    
                         USER        PID ACCESS COMMAND
    /dev/dsp             root       1225 f....  mp3blaster
                         root       1282 f....  mp3blaster
					

    audio:x:29:p,wellspring
					

10.1. Apple 8-bit

All the 8-bit Apple ][ emulators require a copy of the original ROM, for whichever system you want to emulate, in a file. If you search hard enough, you can find file copies of the ROMs for the Apple ][, ][+, ][e, ][c and //gs. They are still copyrighted by Apple, and you can only use them legally if you actually own one of these computers.

10.2. DOS

10.3. Win16

10.4. Win32

11.1. SCUMM Engine (LucasArts)

Lucasarts wrote an engine for point and click adventures named SCUMM (Script Creation Utility for Maniac Mansion). They wrote many graphical adventures using SCUMM, like their famous Monkey Island series (all three). Ludvig Strigeus <strigeus@users.sourceforge.net> was able to reverse engineer the SCUMM format and write an interpreter for SCUMM based games that compiles under Linux and Win32 named scummvm <http://scummvm.sourceforge.net/>. Their website is very good, and chock full of any kind of information about SCUMM and playing these games under scummvm.

A compatibility page is maintained at the scummvm website. FWIW, I've been able to finish many of the games that are listed as 90% done with no problems. scummvm is rock solid, and allows you to purchase SCUMM based Lucas Arts games, copy the data files to your hard drive and play them under Linux. As of February 2002, I've been following their cvs, and this project is undergoing constant development. Kudos to the scummvm team.

11.2. AGI: Adventure Gaming Interface (Sierra)

The older Sierra DOS graphical adventure games used a scripting language named AGI (Adventure Gaming Interface). Some examples of games written in AGI would be Leisure Suit Larry I (EGA), Space Quest I and II, King's Quest II, Mixed-Up Mother Goose and others. These games can be played using sarienon> <http://sarien.sourceforge.net>, an open source interpreter for AGI games.

Sarien was written in SDL, so it should run on any platform that can compile SDL programs. In addition, there are versions for DOS, Strong-Arm based pda's, QNS (holy cow! embedded gaming!), MIPS based systems and SH3/4 based Pocket PC's. The developers are clearly out of their minds (in a good way!). Sarien also has numerous enhancements not found in the original games, like a Quake style pull-down console, picture and dictionary viewer, enhanced sound and support for AGDS, a Russian AGI clone. Sarien is under development and the developers have been very good about documenting the Sarien internals if anyone wants to get involved in hacking it.

11.3. SCI: SCript Interpreter or Sierra Creative Interpreter (Sierra)

The newer Sierra graphical adventure games (we're talking about the late 80's here) used an interpreter named SCI. There were many versions of SCI since Sierra was constantly improving its engine. The original SCI games were DOS based, but Sierra eventually started releasing Win32 SCI based games. Some examples of games written with SCI are Leisure Suit Larry 1 (VGA), Leisure Suit Larry 2-7, Space Quest 3-6, King's Quest 4-6, Quest For Glory 1-4 and many others. Compared with AGI games, SCI adventures have better music support, a more complex engine and loads of bells and whistles.

Many SCI based games (games written in SCI0) can be played using freesci, available at http://freesci.linuxgames.com. Like Sarien, FreeSCI has many graphics targets including SDL, xlib and GGI, so this game can compile and run under an incredible number of platforms. The developers have done a fantastic job of documenting and FAQing their application.

11.4. Infocom Adventures (Infocom, Activision)

The Z-machine is a well documented <http://www.gnelson.demon.co.uk/zspec/index.html> virtual machine designed by Infocom to run their interactive fiction games. This allowed them to write game data files in a cross platform manner, since only the engine itself, the Z-machine, would be platform dependent. Z-machine went through a number of revisions during the lifetime of Infocom, and two further revisions (V7 and V8 created by Graham Nelson) after the Infocom's demise. The later versions even supported limited sound and graphics!

One of the most popular Z-machine interpreters is Frotz <http://www.cs.csubak.edu/~dgriffi/proj/frotz/>. This excellently done page has many nice links for interactive fiction fans. Frotz is GPL, runs all versions of Z-machine and will compile on most versions of Unix. Frotz has spawned many forks, like a version for PalmOS and Linux based PDA's.

jzip <http://jzip.sourceforge.net/> is another very popular Z-machine interpreter that will run V1-V5 and V8 Z-machine data files. jzip is very portable; it compiles on all Unices, OS/2, Atari ST and DOS.

There are actually many other Z-machine interpreters like nitfol and rezrov (written in Perl!). Each interpreter has its own set of strengths, and you can find links to them on the home pages for Frotz and jzip.

11.5. Scott Adams Adventures (Adventure International)

Scott Adams is, arguably, the father of interactive fiction. Although he himself was inspired by the first piece of interactive fiction, Adventure, Scott brought adventuring to the masses. His games were available for Atari, Apple 2, Commodore, Sorcerer, TI, and CPM. His company, Adventure International, released a number of much loved games between 1978 and 1984 before folding. He recently released a new game (a Linux version is not available) but since the decline of adventuring, he has pretty much kept out of the gaming industry.

Alan Cox wrote scottfree, a Scott Adams adventure game file interpreter for Unix. Using scottfree and any of the Scott Adams data files which can be downloaded from Scott's website <http://www.msadams.com/> you can enjoy these classics.

11.6. Ultima Underworld: The Stygian Abyss (Origin, Blue Sky Productions)

The Underworld Adventures project <http://uwadv.sourceforge.net/> is an effort to port the 1992 classic, Ultima Underworld: The Stygian Abyss, to modern operating systems like Linux, MacOS X, and Windows. It uses OpenGL for 3D graphics, SDL for platform specific tasks and is released under the GNU GPL. Underworld Adventures provides an impressive graphics system which uses the original game files, so you'll need the original game disk to play.

Underworld Adventures also provides a bunch of tools for you to display the level maps, tools for examining uw1 conversation scripts and more.

11.7. Ultima 7 (Origin, Electronic Arts)

Ultima 7 is actually 2 games: part I (The Black Gate) and part II (Serpent Island) which uses a slightly enhanced version of The Black Gate's engine. In addition, an addon disk was released to both part I (The Forge Of Virtue) and part II (The Silver Seed).

A team of people developed Exulton> <http://exult.sourceforge.net/> which is an open source interpreter that will run both parts of Ultima 7 and their addon disks. Exult is written in C++ using SDL, so it will compile on any platform that can compile SDL programs. It also features some enhancements over the original versions of the Ultima VII engine. You'll need to purchase a copy of Ultima 7 to play. The developers have no plans on extending Exult to interpret the other Ultimas since the engines changed so radically between releases.

The Exult team has also been hard at work creating a map editor, Exult Studio, and a script compiler that will let users create their own RPG in the Ultima style.

11.8. System Shock (Electronic Arts, Origin)

System Shock is a classic first person shooter/adventure from 1994, which puts it as a contemporary of Doom. However, its engine is much more feature rich than the original Doom: for example, System Shock had 3D sprites, free look and a facility to have objects on top of each other, giving the illusion of a full 3D map, like Quake. Game reviewers agree that this game has the features of Quake with a story-line more compelling than Half-life. The System Shock engine was optimized for sophistication, while Doom's engine was optimized for throwing lots of monsters at you; a completely different appoach. Quite impressive for such an old game!

The System Shock Hack Project <http://madeira.physiol.ucl.ac.uk/tsshp/sshock.html> is an attempt to update the game for modern operating systems. The project uses SDL and is released under the modified BSD license. While you need the original game files to play SSHP, it should work with the System Shock demo, which is freely available.

12.1. Meta gaming websites

These are some resources for Linux gamers no matter what kind of game you enjoy to play.

12.2. Commercial Linux Game Resources

12.3. Other Resources

This section has URL's that should be mentioned but didn't have a separate section within the howto, so I list them here as a kind of appendix.