background layers, scaling of sprites as they moved towards or away from the player's view, or other rendering methods such as the SNES's Mode 7. These tricks to simulate 3D-rendeder graphics through 2D systems are generally referred to as 2.5D graphics. True real-time 3D rendering using polygons were soon popularized by Yu Suzuki's Sega AM2 games Virtua Racing (1992) and Virtua Fighter (1993), both running on the Sega Model 1 arcade system board; some of the Sony Computer Entertainment (SCE) staff involved in the creation of the original PlayStation video game console credit Virtua Fighter as inspiration for the PlayStation's 3D graphics hardware. According to SCE's former producer Ryoji Akagawa and chairman Shigeo Maruyama, the PlayStation was originally being considered as a 2D-focused hardware, and it wasn't until the success of Virtua Fighter in the arcades that they decided to design the PlayStation as a 3D-focused hardware. Texture mapping and texture filtering were soon popularized by 3D racing and fighting games. Home video game consoles such as the PlayStation, the Sega Saturn, and Nintendo 64 also became able to produce texture-mapped 3D graphics. Nintendo had already released Star Fox in 1993 which included the Super FX graphics co-processor chip built into the game cartridge to support polygonal rendering for the SNES, and the Nintendo 64 included a graphics coprocessor on the console directly. On personal computers, John Carmack and John Romero of id Software had been experimenting with real-time rendering of 3D games through Hovertank 3D and Catacomb 3-D. These led to the release of Wolfenstein 3D in 1992, considered to be the original first-person shooter as it rendered the game's world fast enough to keep up with the player's movements. However, at this point, Wolfenstein 3D maps were restricted to a single flat level. Improvements would come with Ultima Underworld from Blue Sky Productions, which included floors of different heights and ramps, which took longer to render but was considered acceptable in the role-playing game, and id's Doom, adding lighting effects among other features, but still with limitations that maps were effectively two-dimensional and with most enemies and objects represented by sprites in-game. id had created one of the first game engines that separated the content from the gameplay and rendering layers, and licensed this engine to other developers, resulting in games such as Heretic and Hexen, while other game developers built their own engines based on the concepts