Glide is a 3D graphics API developed by 3dfx Interactive for their Voodoo Graphics 3D accelerator cards. Although it originally started as a proprietary API, it was later open sourced by 3dfx. It was dedicated to gaming performance, supporting geometry and texture mapping primarily, in data formats identical to those used internally in their cards. Wide adoption of 3Dfx led to Glide being extensively used in the late 1990s, but further refinement of Microsoft's Direct3D and the appearance of full OpenGL implementations from other graphics card vendors, in addition to growing diversity in 3D hardware, eventually caused it to become superfluous.
Glide is based on the basic geometry and "world view" of OpenGL. OpenGL is a large graphics library with 336 calls in the API, many of which are of limited use. Glide was an effort to select primarily features that were useful for real-time rendering of 3D games. The result was an API that was small enough to be implemented entirely in late-1990s hardware. However, this focus led to various limitations in Glide, such as a 16-bit color depth limit in the display buffer.
Use in games 
The combination of the hardware performance of Voodoo Graphics (Voodoo 1) and Glide's easy-to-use API resulted in Voodoo cards generally dominating the gaming market during the latter half of the 1990s. The name Glide was chosen to be indicative of the GL underpinnings, while being different enough to avoid trademark problems.
Glide wrappers and emulators 
Glide emulator development has been in progress since the late 1990s. During 3dfx's lifetime, the company was aggressive at trying to stop these attempts to emulate their proprietary API, shutting down early emulation projects with legal threats. However, just before it ceased operations and had its assets purchased by NVIDIA, 3dfx released the Glide API, along with the Voodoo 2 and Voodoo 3 specifications, under an open source license, which later evolved into an open source project. Although no games released after 1999 depend on Glide for 3D acceleration (Direct3D and OpenGL are used instead), Glide emulation is still needed to run older games in hardware accelerated mode. With the specifications and code now open source, there are several capable emulators and wrappers available allowing older games that make use of the Glide API to run on non-Voodoo hardware. Other projects like Glidos allow even older games to use Glide.
See Also 
-  The 3DFX GLIDE Source Code General Public License
- http://www.gamers.org/dEngine/xf3D/glide/glidepgm.htm GLIDE programming manual
- 3dfx wraps up wrapper Web sites, The Register, April 8, 1999.