Transform and Lighting

With Transform and Lighting (or short- T & L , English for "transformation and illumination") are two steps of graphics pipeline in the 3D computer graphics called. Transform and Lighting as a separate expression is mainly used in connection with graphics cards that can perform these steps themselves and thus relieve the main processor.

“Transform” describes the transformation of the world coordinates of a vertex into two-dimensional screen coordinates using a transformation matrix . Since both the world coordinates (object moves in the virtual world) and the transformation matrix (“camera” moves or changes its zoom ) can constantly change, the transformation must be carried out anew for each image.

"Lighting" refers to the calculation of the lighting of a pixel, ie its brightness and color, according to the lighting model . For some simple models such as the important Phong model , a calculation of the angle between the surface normal and the direction of the light source is necessary and decisive. This angle must also be calculated for each image, since the position of the object can change relative to the light source.

Both of the operations that must be performed on each vertex are simple vector and matrix operations. They can be easily implemented in hardware, since flexibility is not required here. Since the calculations are also independent of one another, they can be parallelized to almost any degree. Such a realization in hardware exceeds the speed of a software implementation many times over.

First, the functionality was implemented in the Savage 2000 graphics chip from S3 Inc. and the NVIDIA GeForce 256 and called "Transform and Lighting (T&L) engine" by the manufacturers, from which Transform and Lighting originates as an independent term. This feature is now supported by all modern chips, from version 7.0 it is an integral part of the DirectX function catalog. For graphics cards without a T&L unit, the steps were either carried out by the program itself or by the 3D driver and calculated by the CPU in both cases .