In the first half of 1993, Carmack worked on improving the graphics engine. After Romero's level designs started to cause engine problems, he researched and began to use binary space partitioning to quickly select the portion of a level that the player could see at any given time. In March 1993, the team stopped work on "Doom" to spend three weeks building a Super Nintendo Entertainment System port of "Wolfenstein 3D", after the contractor hired for the port had made no progress. Taylor, along with programming other features, added cheat codes; some, such as "idspispopd", were based on ideas their fans had come up with while eagerly awaiting the game. By late 1993, "Doom" was nearing completion and player anticipation was high, spurred on by a leaked press demo. John Carmack began to work on the multiplayer component; within two weeks he had two computers playing the same game over the internal office network. Soon, the office was playing four-player deathmatch games.