3. A first look at the Doom Engine

The Doom Engine was written in Watcom C by John Carmack, John Romero and Dave Taylor. It runs on DOS and is capable of generating 256 colour graphics. The game will run well on any machine above a 486, and it requires 8 MB of RAM.

In Doom the player finds himself on a lost moon base on Mars, infested with monsters from another dimension. The game is divided into a number of areas, called levels, which a player must complete. Each level consists of a number of structures such as rooms, large open areas, tunnels, dark and bright areas, etc., and there are various objects in the level that the player can interact with. There are enemies to shoot, weapons and other items that the player can pick up.

Let us then look at what the Doom engine must handle -

• Once the program starts, the player can select a difficulty setting and a level to play on.
• The Engine generates graphics depending on the player's movements and adjusts lighting accordingly.
• The enemies are programmed to follow the player and attack him.
• The Engine must keep track of the positions of the player at all times and the status of all other objects in the game, right until the player exits the game.

Although Doom looks three-dimensional, the representation of the level is two-dimensional. No object can ever be on top of any other object. However, rooms, and other areas can have different floor and ceiling heights, giving the impression of being in a 3D world.

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