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Game Sprocket Intro

Volume Number: 13 (1997)
Issue Number: 2
Column Tag: Game Development

Sprockets are Forever

By Jeremy Vineyard, Viperware

Macs Were Made to Play Games

The Beginning...

When I was a child, I used to beg my parents for quarters to play in the local arcade. Wasting thousands of hours with this activity, I developed a passion for creating games. The desire to create my own games magnified with every quarter I spent.

Reality is often harsh, especially for the would-be game developer. I discovered that games can be very difficult to write. A good game developer must have extensive knowledge of animation techniques, music composition, sound recording, graphics synchronization, algorithm design, data structures, and more. Game developers lose sleep over the slowdown caused by CD-quality sound and full-screen scrolling graphics, and the complexities of an arcade game type environment. Until fairly recently, there wasn't much documentation explaining how to write games, if you wanted to learn, you did so by trial and error.

Not long ago, Apple officially announced something that Mac lovers have known for years: the Mac is a game machine. In fact, the Mac is a great game machine, featuring built-in support for high-resolution graphics and CD-quality sound. Along with this announcement, Apple resolved to help Mac game developers write even cooler games for the Mac. The result - Apple's Game Sprockets.

What is a Sprocket?

A sprocket is a component of Apple's new game development architecture. Each sprocket adds extra features to the MacOS that specifically benefit those who are writing games. There are six sprockets currently under development by Apple: DrawSprocket, SoundSprocket, InputSprocket, NetSprocket, SpeechSprocket, and QuickDraw 3D Rave. SpeechSprocket is just a repackaged version of Apple's Speech Recognition Manager. Game Sprockets will run only on PowerMacs, but certain sprockets may be ported to 68k in the future. Game Sprockets require the newest system software including OpenTransport 1.1, Display Manager 2.0, and Sound Manager 3.2.1.


Prepare for battle! Flames rupture your view; sirens wail. You have the enemy in your sights. Fire! The screen jerks and the action grinds to a halt. Unexpectedly, you find yourself waiting for the screen to refresh. As the computer calculates the next frame of animation, your senses are brought to terms with reality. You lose interest, quit, and go to your living room to read a book. Full-screen, high-resolution graphics are quite possibly the bane of all computer games.

The Macs make great game machines, but they lack certain characteristics that make the primeval PCs more suitable for playing games. One noticeable shortcoming is that unlike PC's, most Macs don't have page-flipping. Page-flipping is the ability to almost instantly switch frames of animation by simply telling the display device (the monitor) to look somewhere else in memory for the display data (the graphics). DrawSprocket provides transparent support for page-flipping on the Macs that support it, and falls back on more compatible methods for those that don't. When page-flipping is not available, DrawSprocket reverts to using CopyBits, which is much slower than page-flipping because QuickDraw must copy the entire contents of each frame of animation onto the screen.

DrawSprocket also supports multi-buffering, with which the next frame of animation can be drawn even while the current frame is being copied to the screen. Multi-buffering can decrease the animation bottleneck that occurs when the processor overtakes the speed of the display device.

Figure 1. Select a Display with DrawSprocket.

DrawSprocket offers common game-related tasks such as a user interface for selecting monitors and providing an easy way for games to take control of the entire screen, which includes hiding the menu bar and blanking all unused monitors. DrawSprocket takes care of fading the screen to any color by altering a monitor's gamma tables. This is good for making a cool fade, setting up the screen for the next scene, and fading back into the game.

DrawSprocket makes it easy for you to include an underlay in your game. An underlay is an image that is always behind all other graphical elements. For example, you might have a scrolling picture of a mountain that is always in the background. In the future, DrawSprocket will support overlays allowing game developers to easily implement foreground images.

DrawSprocket's routines can provide your game with a consistent frame rate so that the animations don't change speed when they are becoming more or less processor-intensive. For the animated elements, Apple provides a sprite manager within QuickTime.


Have you been frustrated while trying to use a Mac joystick? Until the introduction of InputSprocket, the Mac had no built-in support for game input devices, resulting in emulated performance by the Mac joysticks, flight sticks, and game pads.

InputSprocket is an API for the Mac joystick developers that provides a consistent user experience when using joysticks and other game-related input devices on the Mac. Joystick manufacturers write drivers for their devices that communicate with games about the elements of the joystick. Some examples of elements are buttons, controllers, directional pads, and others that are common to game-related input devices. Games that use InputSprocket can interact directly with these elements, eliminating the need for the elements to be emulated through the mouse or keyboard.

You can create your own interface for choosing the active game device and assigning functions to game controls, but InputSprocket provides a standard user interface for you.

Figure 2. InputSprocket Interface.

For a game input device to work with InputSprocket, a driver must be written for that device. As of the writing of this article, no joystick manufacturers shipped InputSprocket drivers for their products, but companies such as Gravis and Thrustmaster have demonstrated prototype InputSprocket drivers. InputSprocket has problems working with some third-party input devices such as Kensington mice, but Apple developers are working to fix this problem.

QuickDraw 3D RAVE

QuickDraw 3D RAVE (Rendering Acceleration Virtual Engine) is a Hardware Abstraction Layer (HAL) that allows game developers who write their own 3D rendering engines (as does Bungie for Marathon) to take advantage of the features offered by 3D accelerator cards when they are present. QuickDraw 3D Rave is a stripped-down version of QuickDraw 3D, and it is highly optimized, making it ideal for game developers who need every amount of speed they can get.

Games communicate with QuickDraw 3D RAVE by converting their rendered images into triangles, which RAVE then sends to the accelerator card if present, or otherwise emulates in software. In addition to supporting 3D accelerator cards, RAVE will soon be cross-platform, allowing game developers to easily port their low-level 3D rendering code.


3D games are the rage nowadays. This is evident by the huge sales of games like Doom and Marathon. Along with freedom of movement comes the responsibility to make the user experience as realistic as possible. Players are expecting to be drawn into their games more and more as computer processing power increases. 3D sound adds an extra dimension of reality and helps the game developer write really cool games.

Figure 3. Configuring a Sound Device for 3D Sound.

SoundSprocket adds the capability of making sounds appear to come from positions relative to the game player. This allows realistic feedback such as: "The aliens are to my left!" and can make game play much more enjoyable. Like all the other sprockets, SoundSprocket provides a standard user interface for configuring sound output devices to take maximum advantage of their 3D sound capabilities.

Future versions of SoundSprocket promise to add effects such as altering sound as it travels through the environment. Sound will be heard differently based on the humidity of the environment, and will even be able to travel through dense fog or water. Sound will also reverberate by bouncing off walls.

You don't have to have a 3D game to benefit from 3D sound. Most games that use sound effects can benefit from more realistic sound and a more in-depth user experience.


As adrenaline pulses through your veins, your finger slips from sweat as you pull at the trigger. The force from the rocket blast kicks you back. Splat! A direct hit. You drool in ecstasy as your opponent's corpse splatters to the ground. Are you competing in Bloodsport? No- you have just finished off the last of your assailants in a networked game of Marathon. Unlike competing against a personality-less computer, going head-to-head with your best friends (or even your enemies) can be a heck of a good time.

Macs have been one of the easiest platforms to network together since their introduction. Setting up a local area network is as simple as connecting a cable between two Macs. This ease of use takes most of the pain out of adding networking to Mac games. However, because there are many different protocols that a network might support (IP, IPX, AppleTalk, Serial, etc.), a game developer probably won't have time to implement all of these protocols in addition to testing the reliability of their network code.

NetSprocket provides a set of high-level routines designed specifically to help developers add networking code to their games. NetSprocket hides the low-level details of the network from the programmer and takes care of many tasks that the developer would otherwise be forced to implement.

Figure 4. Hosting a Network Game.

Figure 5. Joining a Network Game.

NetSprocket is based on a client/server architecture in that one player acting as a server hosts a game session, and other players join as clients to the network game. In the future, NetSprocket will provide more models other than the client/server model for interacting between networked players. NetSprocket hides the implementation details of supporting various protocols, saving the developer time needed to re-write the networking code for each protocol. NetSprocket is fast and fault tolerant - when one computer in the networked game crashes, it doesn't bring down everyone else. Since the low-level network code is already written, NetSprocket can save a game developer hundreds of hours of work.

NetSprocket assigns each player a player ID and a player type. Player types might include referees, observers, and participants. Players can belong to groups (red team, black team, etc.).

A networked game works like a conversation - players pass messages back and forth. This communication activity is known as a protocol. A network protocol is very much like a conversation - players ask questions and wait for responses. Although NetSprocket makes it very easy to pass messages between networked players, knowledge of designing protocols is important. Fortunately, designing protocols is not a difficult topic to learn, and can end up being somewhat addicting. (Or maybe it's just me?)

To Infinity and Beyond

Apple is not supporting 68k machines with its Game Sprockets architecture. Until Apple develops 68k versions of Game Sprockets, Game Sprocket developers must limit their audience to PowerMac users.

Apple has a tarnished reputation for settling for complacency when it releases new technologies to developers (see QuickDraw GX, AOCE). In order for Game Sprockets to thrive, Apple must provide game developers with an abundance of tools, source code, and updates to the existing API. Thankfully, Apple has been doing a good job with Game Sprockets, keeping updates coming steadily and keeping in touch with the developers who use the technologies.

Apple's Game Sprockets are definitely a step in the right direction if they want to remain a competitive OS solution into the future. I look forward to seeing games released that take advantage of the features that are offered. Thank you to those people within Apple who are working hard to bring more cool games to the Mac!


The Internet is a great place to find information on Apple's Game Sprocket architecture. Here are some URL's that can help you get started.

Apple's Game Sprocket Page

Developer University Course- Game Development with Sprockets

Licorice Web Page for Game Sprocket Developers


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