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Geometry pipelines 46
Geometry pipelines
Geometric manipulation of modeling primitives, such as that performed by a geometry pipeline, is the first stage in
computer graphics systems which perform image generation based on geometric models. While Geometry Pipelines
were originally implemented in software, they have become highly amenable to hardware implementation,
particularly since the advent of very-large-scale integration (VLSI) in the early 1980s. A device called the Geometry
Engine developed by Jim Clark and Marc Hannah at Stanford University in about 1981 was the watershed for what
has since become an increasingly commoditized function in contemporary image-synthetic raster display systems. [1]
[2]
Geometric transformations are applied to the vertices of polygons, or other geometric objects used as modelling
primitives, as part of the first stage in a classical geometry-based graphic image rendering pipeline. Geometric
computations may also be applied to transform polygon or patch surface normals, and then to perform the lighting
and shading computations used in their subsequent rendering.
History
Hardware implementations of the geometry pipeline were introduced in the early Evans & Sutherland Picture
System, but perhaps received broader recognition when later applied in the broad range of graphics systems products
introduced by Silicon Graphics (SGI). Initially the SGI geometry hardware performed simple model space to screen
space viewing transformations with all the lighting and shading handled by a separate hardware implementation
stage, but in later, much higher performance applications such as the RealityEngine, they began to be applied to
perform part of the rendering support as well.
More recently, perhaps dating from the late 1990s, the hardware support required to perform the manipulation and
rendering of quite complex scenes has become accessible to the consumer market. Companies such as NVIDIA and
ATI (now a part of AMD) are two current leading representatives of hardware vendors in this space. The GeForce
line of graphics cards from NVIDIA were the first to implement hardware geometry processing in the consumer PC
market, while earlier graphics accelerators by 3Dfx and others had to rely on the CPU to perform geometry
processing.
This subject matter is part of the technical foundation for modern computer graphics, and is a comprehensive topic
taught at both the undergraduate and graduate levels as part of a computer science education.
References
[1] Clark, James (July 1980). "Special Feature A VLSI Geometry Processor For Graphics" (http:/ / www. computer. org/ portal/ web/ csdl/ doi/
10. 1109/ MC. 1980. 1653711). Computer: pp. 59–68. .
[2] Clark, James (July 1982). "The Geometry Engine: A VLSI Geometry System for Graphics" (http:/ / accad. osu. edu/ ~waynec/ history/ PDFs/
geometry-engine. pdf). Proceedings of the 9th annual conference on Computer graphics and interactive techniques. pp. 127-133. .