Doom was one of the first games to be developed with 3D rendering technology as was its predecessor Wolfestein 3D, for the graphics engine of Doom (ID Tech1) they took the Wolfestein 3D graphics engine, but improved it to suit the needs of the game. Because they wanted a fast game, the texturing speed of Wolfestein 3D was not fast enough and did not allow the computers of the time to render the game correctly, so one day John Carmak read about a programming process to help render three-dimensional models on the screen (BSP) that they were using at Bell Labs. This gave him an idea, if he could use it for the game, the rendering problems would be over.
Space partitioning is a way of recursively dividing a plane into two convex sets (spaces that are partitioned and belong to the same space).
Thanks to the BSP the image of a room would be divided into a giant tree of planes and the computer would only draw the planes that are convex to the camera plane instead of drawing the whole level.
Doom implemented two online game modes, the first and default was the co-op mode where two players fought monsters together. The second was deathmatch in which two to four players fought each other and each time they died they earned a point, this was subtracted if they committed suicide or died on the ground.
To differentiate the players a way of identification was implemented for each player, this was to change the colour of the suit for it was used the function "( R_DrawTranslatedColumn)" that compensated for the shade of green in the sprite.
Doom also contained a communication system to talk to other players, by pressing the "T" key you could talk in a global chat, and by pressing "G,I,B,R" you could communicate privately with one of the players, every 1/35 seconds a letter was stored and placed in a queue, which would then be read by the rest of the players.
Early versions of Doom included support for IPX networks within the Doom executable. Later, this was replaced with a modular system that included two executables, IPXSETUP.EXE and SERSETUP.EXE. Once a connection has been established, the driver will invoke the main Doom, Heretic or Hexen executable.
When starting the game, the driver passes a command line -netparameter. This is used to specify the memory address of a structure within the driver's memory.
The degrading effect on the IPX network due to network overload, affecting computers that were not playing the game, forced system administrators in many office networks to ban Doom.
id software released the source code for doom, the community began to develop multiple versions of the game, and source ports.
Some of the ports that this release entailed :
