Game Sprocket Intro
Volume Number: 13
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.
DrawSprocket
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.
InputSprocket
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.
SoundSprocket
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.
NetSprocket
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!
Footnote
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
http://dev.info.apple.com/evangelism/games/games.html
Developer University Course- Game Development with Sprockets
http://devworld.apple.com/dev/du/Using_Game_Sprockets/Using_Sprockets.html
Licorice Web Page for Game Sprocket Developers
http://www.viperware.com/licorice