Transform, clipping, and lighting
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Transform, clipping, and lighting (T&L or sometimes TCL) is a term used in computer graphics.
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[edit] Description
Transform is the task of converting spatial coordinates, which in this case involves moving three-dimensional objects in a virtual world and converting the coordinates to a two-dimensional view. Clipping means only drawing things that might be visible to the viewer. Lighting is the task of taking light objects in a virtual scene, and calculating the resulting colour of surrounding objects as the light falls upon them.
[edit] Hardware
T&L had been implemented in software until 2000, and it was initially believed that a faster CPU would be able to keep pace. However, 3D computer games have increasingly complex scenes and detailed lighting effects, so the larger number of geometry calculations has become more computationally intense.
Nvidia's GeForce 256 was released in late 1999, which pioneered consumer hardware support for T&L. Notably, while DirectX 7.0 (particularly Direct3D 7) was the first release of that API to support hardware T&L, OpenGL had supported it much longer and was typically the purview of these older professionally-oriented 3D accelerators which were designed for computer-aided design (CAD) instead of games.
S3 Graphics launched the Savage 2000 accelerator in late 1999, shortly after GeForce 256, but ending up S3 never developing working Direct3D 7.0 drivers that would have enabled hardware T&L support.[1]
[edit] Usefulness
Hardware T&L did not have broad application support in games at the time, so critics contended that it had little real-world value. Initially, it was only somewhat beneficial in a few OpenGL-based 3D first-person shooter titles of the time, most notably Quake III Arena. 3dfx and other competing graphics card companies contended that a fast CPU would make up for the lack of a T&L unit.
ATI's initial response to GeForce 256 was the dual-chip Rage Fury MAXX. By using two Rage 128 chips, each rendering an alternate frame, the card was able to somewhat approach the performance of SDR memory GeForce 256 cards, but the GeForce 256 DDR still retained the top speed.[2] Ending up, ATI developed their own GPU known as the Radeon which also implemented hardware T&L.
3dfx's Voodoo5 5500 did not have a T&L unit but it was able to match the performance of the GeForce 256, although the Voodoo5 was late to market and by its release it could not match the succeeding GeForce 2 GTS.
STMicroelectronics' PowerVR Kyro II, released in 2001, was able to rival the costlier ATI Radeon DDR and NVIDIA GeForce 2 GTS in benchmarks of the time, despite not having hardware transform and lighting. Unfortunately, as more and more games were optimised for hardware transform and lighting, the KYRO II lost its performance advantage and is not supported by most modern games.
Futuremark's 3DMark 2000 heavily utilized hardware T&L, which resulted in the Voodoo 5 and Kyro II both scoring poorly in the benchmark tests, behind budget T&L video cards such as the GeForce 2 MX and Radeon SDR.
[edit] Industry standardization
By 2000, only ATI with their comparable Radeon 7xxx series, would remain in direct competition with Nvidia's GeForce 256 and GeForce 2. By the end of 2001, all discrete graphics chips would have hardware T&L.
Support of hardware T&L assured the GeForce and Radeon of a strong future, unlike its Direct3D 6 predecessors who relied upon software T&L. While hardware T&L does not add new rendering features, an increasing number of games recommended it anyway to run at optimal performance. GPUs that support T&L in hardware are usually considered to be in the DirectX 7.0 generation.
After hardware T&L had become standard in GPUs, the next step in computer 3D graphics was DirectX 8.0 with fully programmable vertex and pixel shaders. Nonetheless, many early games that supported DirectX 8.0 shaders such as Half-Life 2 made that feature optional, so DirectX 7.0 hardware T&L GPUs could still run the game. For instance, the GeForce 256 was supported in games up until approximately 2006, in games such as Star Wars: Empire at War.
