Geometry pipelines: Difference between revisions

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{{Refimprove|date=April 2009}}

'''Geometry Pipelines''', also called Geometry Engines(GE) are the first stage in a classical Graphics Pipeline, such as the [[Reality Engine]]. They do the transformation from 3D coordinates used to specify the geometry to a unified coordinate system used by the [[Raster Manager]] (RM) to rasterize the geometry into framebuffer pixels. The [[Display Generator]](DG) scans these pixels into a video signal understood by a monitor. In [[OpenGL]], this transformation is defined by the [[Modelview Matrix]] and the [[Projection Matrix]]. Typically, the modelview matrix defines the transformation of the incoming vertices into world coordinates, a coordinate system used for all vertices. The projection matrix defines how this 3-dimensional coordinate space is projected to the Viewport. In addition to this transformation, the GEs compute the vertex colors based on the light settings, may perform texture coordinate generation as well as clipping of the geometry. The Geforce graphics cards from nVidia introduced these functionalities for the first time in the consumer market, labelled as hardware-based [[Transform and Lighting]](T&L).

Geometric manipulation of modelling 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 [[James H. Clark|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 graphics|raster display]] systems.<ref>{{Cite journal

| last = Clark

| first = James

| title = Special Feature A VLSI Geometry Processor For Graphics

| pages = 59–68

| journal = Computer

| date = July 1980

| volume = 13

| issue = 7

| doi = 10.1109/MC.1980.1653711

| s2cid = 2428227

}}</ref><ref>{{Cite conference

|first = James

|last = Clark

|title = The Geometry Engine: A VLSI Geometry System for Graphics

|book-title = Proceedings of the 9th annual conference on Computer graphics and interactive techniques

|pages = 127–133

|date = July 1982

|url=https://dl.acm.org/doi/pdf/10.1145/965145.801272 |citeseerx=10.1.1.359.8519 |doi=10.1145/965145.801272

}}

</ref>

[[Geometric transformation]]s are applied to the vertices of [[polygon]]s, or other geometric objects used as [[geometric primitive|modelling primitive]]s, as part of the first stage in a classical geometry-based graphic image [[Artistic rendering|rendering]] pipeline. Geometric computations may also be applied to transform polygon or repair [[surface normal]]s, and then to perform the [[computer graphics lighting|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 transformation]]s with all the lighting and shading handled by a separate hardware implementation stage. 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 [[AMD Graphics]] (formerly [[ATI Technologies|ATI]]) are two current leading representatives of hardware vendors in this space. The [[GeForce]] line of [[graphics card]]s from Nvidia was the first to support full [[OpenGL]] and [[Direct3D]] hardware geometry processing in the consumer PC market, while some earlier products such as Rendition Verite incorporated hardware geometry processing through proprietary programming interfaces. On the whole, earlier graphics accelerators by [[3Dfx]], [[Matrox]] and others relied on the [[Central processing unit|CPU]] for 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.

== See also ==

* [[Vertex pipeline]]

* [[Graphics pipeline]] (include [[Pixel pipeline]])

* [[Rasterisation]]

* [[SiliconOpen Graphics, Inc.Project]]

==References==

* [[Computer graphics]]

{{Reflist}}

* [[James H. Clark]]

* [[Silicon Graphics, Inc.]]

{{Graphics Processing Unit}}

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[[Category:3D computer graphics]]