One feature that was built in from the beginning was a multiplayer option. Id added this feature with an eye toward the future. The Doom designers felt that multiplayer games would become increasingly important as Internet and other forms of commercial networks become part of more homes.
Although Id expects less than 10% of players of Doom to make use of the ability, up to four players can join the same game over a Novell IPX network. Id designers felt it was important to start working on multiplayer games now, so they would have the experience when it was more crucial to their development.
As soon as the network option was added, however, more complications cropped up. For example, the line-of-sight checks that the monsters' AI programming went through were slowing the game because they had to scan for every player. Another problem with the AI routines was that monsters were targeting some players, but ignoring others. These problems were fixed, but there was a minor problem that had to stay in the game.
The sprites for the individual players were drawn holding a generic gun, which wasn't a big issue when there was only one player. But, with multiple players, an opposing player couldn't tell which of the seven different weapons another player had. To give the players this viewpoint seven complete sets of sprites would have to be drawn for the character, and the design team felt it wasn't that important.
The graphics for Wolfenstein were drawn completely by Adrian Carmack, but for the Doom graphics, the Id team knew it was going to need help. It enlisted the aid of professional model designer Gregor Punchatz and created a setup that would easily allow the results to be digitized. Figure 2 shows the final results.
The models are placed on a revolving tray where they are secured to the base. There are eight pegs in the tray that represent the eight points of view that are needed by the game engine to render the creatures. Next, the models are animated frame by frame by moving the model and then rotating it to each specific vantage point the engine uses to display it. The images are digitized by a video camera hooked up to the NeXT machine. When each frame is captured, it is imported over the network into a PC running Electronic Arts' Dpaint, where the photographic source is translated into the resolution of the game. The images are drawn at full brightness, and the game engine varies the contrast for light sourcing.
Sound has generally been a low priority in Id's development process, partially because there is no sound programmer on staff. Sound quality for Doom would be better than in Wolfenstein because it was recorded at 11KHz instead 7KHz. Id feels that 16-bit sound is too much for Doom or any other action game in terms of effort, disk space, and processor time. Id designers were set to support the Roland Sound Canvas and most major sound cards, when they started receiving angry letters from supporters of the Gravis UltraSound card. They thought the UltraSound card would be too hard and too much work to support, but the Id sound contractor trimmed down the Gravis code and UltraSound support was added to the final game.
As good as the gameplay was in Wolfenstein, there was room for improvement. Id took advantage of what it learned from its experience with Wolfenstein to make Doom better. For example, secret doors in Wolfenstein were often indistinguishable from the walls around them, so the only way to find one was to search every wall on the level. With Doom, all secret doors have some distinguishing mark to differentiate them for the player. More weapons were added, each with its own unique flavor. Unfortunately the biggest weapon, the BFG 9000, had to be scaled down because it was so elaborate it slowed the game to a crawl every time it was fired.
Another enhancement was an automapping mode, so players could navigate confusing passages from a two-dimensional, top-down perspective. One deliberate playablity issue that rose from adding the automap feature was that monsters would not be visible, and new mapping doesn't take place while in automapping mode. This limitation came about during playtesting because once the playtesters were in the automap mode, they tended to stay there and not play from the actual three-dimensional game screen. "The game is not a challenge to be efficiently beaten," said John Carmack. "It's something you're supposed to experience."