Linux.com Article DB: Linux Gaming APIs: Chapter 3 of PROGRAMMING LINUX GAMES

Scripting Libraries

Tcl

Tool Command Language (Tcl) is a very simple extension language designed to automate a variety of tools. It often loses out because some people try to use it as a replacement for Perl (which it is not), but its simple syntax and convenient extension mechanism make it an ideal candidate for game scripting. Tcl is good at processing strings, but it is a poor choice for high-volume number crunching and data manipulation. We will implement a game scripting engine with Tcl in Chapter 6.

The command-line Tcl interpreter and extension libraries are available as source and binaries from http://www.scriptics.com. Although Tcl is commercially maintained, it is free software.

Guile and MzScheme

Scheme is a modern programming language that draws heavily from Lisp. It was designed primarily by Guy Steele in 1979, and it has evolved quite a bit since then. Scheme tends to scare away novices due to its prefix notation, its heavy use of recursion, and the simple fact that it is a Lisp derivative, but advanced users generally find it an amazingly expressive language. Scheme can be parsed and executed very quickly, and it is sufficiently powerful to serve as an excellent game scripting language. The decision to use Tcl instead of Scheme for our scripting examples was difficult, but I felt that Tcl would make for more straightforward examples. However, Scheme would probably provide better performance. Guile is the official GNU extension language. It is a reasonably complete Scheme implementation, but its documentation is extremely sparse. You can find it at http://www.gnu.org/guile.

MzScheme is a complete and actively maintained Scheme system from Rice University (and others). It implements the latest official Scheme standard (R5RS) almost completely, and it extends the language in various ways to make it more practical as a general-purpose programming language. MzScheme functions both as a standalone Scheme interpreter and an embeddable scripting library. If you're interested in using Scheme as an extension language, MzScheme would be an excellent choice. It is available at http://www.cs.rice.edu/PLT.

Python and Perl

You're probably familiar with Python and Perl, and you may already be proficient in one of these languages. While most commonly used as standalone scripting languages, Python and Perl can also be embedded in applications to provide modular scripting support. We won't be using these languages in this book (we'll use Tcl instead), but their scripting interfaces are not terribly difficult (very similar to Tcl, which we'll discuss in Chapter 6). Perl is superb at string processing, and Python has a bit of an object oriented slant. Which language is better suited to game development is anybody's guess.

Perl and Python are available from http://www.perl.org and http://www.python.org, respectively, and each language comes with plenty of online documentation.

Networking APIs

Networked gaming is big, and it is here to stay. There are several networking interfaces for Linux, but almost all of them revolve around the BSD sockets API that became a standard part of Unix years ago.

BSD Sockets

A socket is a Unix file descriptor that designates a network connection rather than a file on disk. Sockets can be thought of as telephone handsets; they are communication endpoints through which data can be transferred in either direction. Sockets are most commonly used with TCP/IP, the stack of protocols behind the Internet.

The advantage of programming with TCP/IP sockets is that TCP/IP is an incredibly versatile protocol. Some version of the BSD sockets API can be found in nearly every operating system, including Linux, Windows, BeOS, and Mac OS. TCP/IP can be used for both local (LAN) and wide-area (WAN) networking, and the protocol can be adapted to the nature of a particular game. Chapter 7 focuses on socket programming. Even if you decide to use an additional toolkit for convenience, it is important to understand how sockets and the underlying network protocols operate.

OpenPlay

OpenPlay is the successor to NetSprocket, Apple's network gaming support library. It is a cross-platform library (implemented in C), and it compiles on Linux as well as Windows and MacOS. OpenPlay is released under the terms of the Apple Public Source License, which is a corporate-friendly license that seems to be remotely inspired by the GNU GPL. OpenPlay is a substantial API designed to compete with Microsoft's closed and proprietary DirectPlay. OpenPlay shows promise, but its Linux port is still under development. It remains to be seen whether OpenPlay for Linux will catch on. Some Linux developers seem to distrust Apple (not always for rational reasons), but the finished port of OpenPlay will have a lot to offer. OpenPlay is available on Apple's public source site, http://publicsource.apple.com.

IPX and SPX

Internetwork Packet Exchange (IPX) is a simple networking protocol similar to the Internet's underlying IP protocol, and Sequenced Packet Exchange (SPX) is a higher-level protocol similar to the Internet's TCP protocol. These protocols (often collectively referred to as IPX) were designed by Novell for its NetWare line of products. IPX has fallen out of favor, but it is still used in a number of games. IPX is fine for small private LANs, but it is not ideal for large networks. Should you choose to support IPX in your games, the Linux kernel provides the necessary networking code (via the normal BSD sockets interface). It is not terribly difficult to support both TCP/IP and IPX with the same networking code.

Originally Published: Tuesday, 26 June 2001	Author: John Hall and Loki Software
Published to: develop_articles/Development Articles	Page: 5/6 - [Printable]
Linux Gaming APIs: Chapter 3 of PROGRAMMING LINUX GAMES Today's Linux.com article, derived from Chapter 3 of the book Programming Linux Games by John Hall, takes a look at the various Linux gaming APIs you can use to construct your game. Don't reinvent the wheel, and don't compromise your open source roots, and check out this excerpt from No Starch Press.

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Scripting Libraries Tcl Tool Command Language (Tcl) is a very simple extension language designed to automate a variety of tools. It often loses out because some people try to use it as a replacement for Perl (which it is not), but its simple syntax and convenient extension mechanism make it an ideal candidate for game scripting. Tcl is good at processing strings, but it is a poor choice for high-volume number crunching and data manipulation. We will implement a game scripting engine with Tcl in Chapter 6. The command-line Tcl interpreter and extension libraries are available as source and binaries from http://www.scriptics.com. Although Tcl is commercially maintained, it is free software. Guile and MzScheme Scheme is a modern programming language that draws heavily from Lisp. It was designed primarily by Guy Steele in 1979, and it has evolved quite a bit since then. Scheme tends to scare away novices due to its prefix notation, its heavy use of recursion, and the simple fact that it is a Lisp derivative, but advanced users generally find it an amazingly expressive language. Scheme can be parsed and executed very quickly, and it is sufficiently powerful to serve as an excellent game scripting language. The decision to use Tcl instead of Scheme for our scripting examples was difficult, but I felt that Tcl would make for more straightforward examples. However, Scheme would probably provide better performance. Guile is the official GNU extension language. It is a reasonably complete Scheme implementation, but its documentation is extremely sparse. You can find it at http://www.gnu.org/guile. MzScheme is a complete and actively maintained Scheme system from Rice University (and others). It implements the latest official Scheme standard (R5RS) almost completely, and it extends the language in various ways to make it more practical as a general-purpose programming language. MzScheme functions both as a standalone Scheme interpreter and an embeddable scripting library. If you're interested in using Scheme as an extension language, MzScheme would be an excellent choice. It is available at http://www.cs.rice.edu/PLT. Python and Perl You're probably familiar with Python and Perl, and you may already be proficient in one of these languages. While most commonly used as standalone scripting languages, Python and Perl can also be embedded in applications to provide modular scripting support. We won't be using these languages in this book (we'll use Tcl instead), but their scripting interfaces are not terribly difficult (very similar to Tcl, which we'll discuss in Chapter 6). Perl is superb at string processing, and Python has a bit of an object oriented slant. Which language is better suited to game development is anybody's guess. Perl and Python are available from http://www.perl.org and http://www.python.org, respectively, and each language comes with plenty of online documentation. Networking APIs Networked gaming is big, and it is here to stay. There are several networking interfaces for Linux, but almost all of them revolve around the BSD sockets API that became a standard part of Unix years ago. BSD Sockets A socket is a Unix file descriptor that designates a network connection rather than a file on disk. Sockets can be thought of as telephone handsets; they are communication endpoints through which data can be transferred in either direction. Sockets are most commonly used with TCP/IP, the stack of protocols behind the Internet. The advantage of programming with TCP/IP sockets is that TCP/IP is an incredibly versatile protocol. Some version of the BSD sockets API can be found in nearly every operating system, including Linux, Windows, BeOS, and Mac OS. TCP/IP can be used for both local (LAN) and wide-area (WAN) networking, and the protocol can be adapted to the nature of a particular game. Chapter 7 focuses on socket programming. Even if you decide to use an additional toolkit for convenience, it is important to understand how sockets and the underlying network protocols operate. OpenPlay OpenPlay is the successor to NetSprocket, Apple's network gaming support library. It is a cross-platform library (implemented in C), and it compiles on Linux as well as Windows and MacOS. OpenPlay is released under the terms of the Apple Public Source License, which is a corporate-friendly license that seems to be remotely inspired by the GNU GPL. OpenPlay is a substantial API designed to compete with Microsoft's closed and proprietary DirectPlay. OpenPlay shows promise, but its Linux port is still under development. It remains to be seen whether OpenPlay for Linux will catch on. Some Linux developers seem to distrust Apple (not always for rational reasons), but the finished port of OpenPlay will have a lot to offer. OpenPlay is available on Apple's public source site, http://publicsource.apple.com. IPX and SPX Internetwork Packet Exchange (IPX) is a simple networking protocol similar to the Internet's underlying IP protocol, and Sequenced Packet Exchange (SPX) is a higher-level protocol similar to the Internet's TCP protocol. These protocols (often collectively referred to as IPX) were designed by Novell for its NetWare line of products. IPX has fallen out of favor, but it is still used in a number of games. IPX is fine for small private LANs, but it is not ideal for large networks. Should you choose to support IPX in your games, the Linux kernel provides the necessary networking code (via the normal BSD sockets interface). It is not terribly difficult to support both TCP/IP and IPX with the same networking code.
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