In May 1992, id Software released "Wolfenstein 3D." It is often referred to as being the "grandfather of 3D shooters", specifically first-person shooters, because it established the fast-paced action and technical prowess commonly expected in the genre and greatly increased the genre's popularity. Immediately following its release, most of the team began work on a set of new "Wolfenstein" episodes, "Spear of Destiny". As the episodes used the same game engine as the original game, id co-founder and lead programmer John Carmack instead focused on technology research for the company's next game, just as he had experimented with creating a 3D game engine prior to the development of "Wolfenstein 3D". Between May and "Spear of Destiny"s release in September 1992, he created several experimental engines, including one for a racing game, before working on an enhanced version of the "Wolfenstein" engine to be licensed to Raven Software for their game "ShadowCaster". For this engine, he developed several enhancements to the "Wolfenstein" engine, including sloped floors, textures on the floors and ceilings in addition to the walls, and fading visibility over a distance. The resulting engine was much slower than the "Wolfenstein" one, but was deemed acceptable for an adventure game like "ShadowCaster".