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Render Output unit 160
Render Output unit
The Render Output Unit, often abbreviated as "ROP", and sometimes called (perhaps more properly) Raster
Operations Pipeline, is one of the final steps in the rendering process of modern 3D accelerator boards. The pixel
pipelines take pixel and texel information and process it, via specific matrix and vector operations, into a final pixel
or depth value. The ROPs perform the transactions between the relevant buffers in the local memory - this includes
writing or reading values, as well as blending them together.
Historically the number of ROPs, texture units, and pixel shaders have been equal. However, as of 2004, several
GPUs have decoupled these areas to allow optimum transistor allocation for application workload and available
memory performance. As the trend continues, it is expected that graphics processors will continue to decouple the
various parts of their architectures to enhance their adaptability to future graphics applications. This design also
allows chip makers to build a modular line-up, where the top-end GPU are essentially using the same logic as the
low-end products.
Rendering
Rendering is the process of generating an image from a model (or models in what
collectively could be called a scene file), by means of computer programs. A scene
file contains objects in a strictly defined language or data structure; it would contain
geometry, viewpoint, texture, lighting, and shading information as a description of
the virtual scene. The data contained in the scene file is then passed to a rendering
program to be processed and output to a digital image or raster graphics image file.
The term "rendering" may be by analogy with an "artist's rendering" of a scene.
Though the technical details of rendering methods vary, the general challenges to
overcome in producing a 2D image from a 3D representation stored in a scene file
are outlined as the graphics pipeline along a rendering device, such as a GPU. A
GPU is a purpose-built device able to assist a CPU in performing complex rendering
calculations. If a scene is to look relatively realistic and predictable under virtual
lighting, the rendering software should solve the rendering equation. The rendering
equation doesn't account for all lighting phenomena, but is a general lighting model
for computer-generated imagery. 'Rendering' is also used to describe the process of
calculating effects in a video editing file to produce final video output.
Rendering is one of the major sub-topics of 3D computer graphics, and in practice
always connected to the others. In the graphics pipeline, it is the last major step,
giving the final appearance to the models and animation. With the increasing
sophistication of computer graphics since the 1970s, it has become a more distinct
subject.
A variety of rendering techniques
applied to a single 3D scene