The additions match those of the SGIS texture edge clamp extension.

D.7 Texture Level of Detail Control

Two constraints related to the texture level of detail parameter λ are added. One constraint clamps λ to a specified floating point range. The other limits the selection of mipmap image arrays to a subset of the arrays that would otherwise be considered.

Together these constraints allow a large texture to be loaded and used initially at low resolution, and to have its resolution raised gradually as more resolution is desired or available. Image array specification is necessarily integral, rather than continuous. By providing separate, continuous clamping of the λ parameter, it is possible to avoid ”popping” artifacts when higher resolution images are provided.

The additions match those of the SGIS texture lod extension.

D.8 Vertex Array Draw Element Range

A new form of DrawElements that provides explicit information on the range of vertices referred to by the index set is added. Implementations can take advantage of this additional information to process vertex data without having to scan the index data to determine which vertices are referenced.

The additions match those of the EXT draw range elements extension.

D.9 Imaging Subset

The remaining new features are primarily intended for advanced image processing applications, and may not be present in all GL implementations. The are collectively referred to as the imaging subset.

D.9.1 Color Tables

A new RGBA-format color lookup mechanism is defined in the pixel transfer process, providing additional lookup capabilities beyond the existing lookup. The key difference is that the new lookup tables are treated as one-dimensional images with internal formats, like texture images and convolution filter images. Thus the new tables can operate on a subset of the components of passing pixel groups. For example, a table with internal format ALPHA modifies only the A component of each pixel group, leaving the R, G, and B components unmodified.

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Three independent lookups may be performed: prior to convolution; after convolution and prior to color matrix transformation; after color matrix transformation and prior to gathering pipeline statistics.

Methods to initialize the color lookup tables from the framebuffer, in addition to the standard memory source mechanisms, are provided.

Portions of a color lookup table may be redefined without reinitializing the entire table. The affected portions may be specified either from host memory or from the framebuffer.

The additions match those of the EXT color table and

EXT color subtable extensions.

D.9.2 Convolution

Oneor two-dimensional convolution operations are executed following the first color table lookup in the pixel transfer process. The convolution kernels are themselves treated as oneand two-dimensional images, which can be loaded from application memory or from the framebuffer.

The convolution framework is designed to accommodate three-dimensional convolution, but that API is left for a future extension.

The additions match those of the EXT convolution and

HP convolution border modes extensions.

D.9.3 Color Matrix

A 4x4 matrix transformation and associated matrix stack are added to the pixel transfer path. The matrix operates on RGBA pixel groups, using the equation

C0 = MC,

where

R

G C = B

A

and M is the 4 × 4 matrix on the top of the color matrix stack. After the matrix multiplication, each resulting color component is scaled and biased by a programmed amount. Color matrix multiplication follows convolution.

The color matrix can be used to reassign and duplicate color components. It can also be used to implement simple color space conversions.

The additions match those of the SGI color matrix extension.

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D.9.4 Pixel Pipeline Statistics

Pixel operations that count occurences of specific color component values (histogram) and that track the minimum and maximum color component values (minmax) are performed at the end of the pixel transfer pipeline. An optional mode allows pixel data to be discarded after the histogram and/or minmax operations are completed. Otherwise the pixel data continues on to the next operation unaffected.

The additions match those of the EXT histogram extension.

D.9.5 Constant Blend Color

A constant color that can be used to define blend weighting factors may be defined. A typical usage is blending two RGB images. Without the constant blend factor, one image must have an alpha channel with each pixel set to the desired blend factor.

The additions match those of the EXT blend color extension.

D.9.6 New Blending Equations

Blending equations other than the normal weighted sum of source and destination components may be used.

Two of the new equations produce the minimum (or maximum) color components of the source and destination colors. Taking the maximum is useful for applications such as maximum projection in medical imaging.

The other two equations are similar to the default blending equation, but produce the difference of its left and right hand sides, rather than the sum. Image differences are useful in many image processing applications.

The additions match those of the and

EXT blend subtract extensions.

D.10 Acknowledgements

OpenGL 1.2 is the result of the contributions of many people, representing a cross section of the computer industry. Following is a partial list of the contributors, including the company that they represented at the time of their contribution:

Kurt Akeley, Silicon Graphics

Bill Armstrong, Evans & Sutherland Otto Berkes, Microsoft

Pierre-Luc Bisaillon, Matrox Graphics Drew Bliss, Microsoft

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David Blythe, Silicon Graphics

Jon Brewster, Hewlett Packard

Dan Brokenshire, IBM

Pat Brown, IBM

Newton Cheung, S3

Bill Clifford, Digital

Jim Cobb, Parametric Technology

Bruce D’Amora, IBM

Kevin Dallas, Microsoft

Mahesh Dandapani, Rendition

Daniel Daum, AccelGraphics

Suzy Deffeyes, IBM

Peter Doyle, Intel

Jay Duluk, Raycer

Craig Dunwoody, Silicon Graphics

Dave Erb, IBM

Fred Fisher, AccelGraphics / Dynamic Pictures

Celeste Fowler, Silicon Graphics

Allen Gallotta, ATI

Ken Garnett, NCD

Michael Gold, Nvidia / Silicon Graphics

Craig Groeschel, Metro Link

Jan Hardenbergh, Mitsubishi Electric

Mike Heck, Template Graphics Software

Dick Hessel, Raycer Graphics

Paul Ho, Silicon Graphics

Shawn Hopwood, Silicon Graphics

Jim Hurley, Intel

Phil Huxley, 3Dlabs

Dick Jay, Template Graphics Software

Paul Jensen, 3Dfx

Brett Johnson, Hewlett Packard

Michael Jones, Silicon Graphics

Tim Kelley, Real3D

Jon Khazam, Intel

Louis Khouw, Sun

Dale Kirkland, Intergraph

Chris Kitrick, Raycer

Don Kuo, S3

Herb Kuta, Quantum 3D

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Phil Lacroute, Silicon Graphics Prakash Ladia, S3

Jon Leech, Silicon Graphics Kevin Lefebvre, Hewlett Packard David Ligon, Raycer Graphics Kent Lin, S3

Dan McCabe, S3 Jack Middleton, Sun Tim Misner, Intel

Bill Mitchell, National Institute of Standards Jeremy Morris, 3Dlabs

Gene Munce, Intel William Newhall, Real3D

Matthew Papakipos, Nvidia / Raycer Garry Paxinos, Metro Link Hanspeter Pfister, Mitsubishi Electric

Richard Pimentel, Parametric Technology Bimal Poddar, IBM / Intel

Rob Putney, IBM Mike Quinlan, Real3D

Nate Robins, University of Utah Detlef Roettger, Elsa

Randi Rost, Hewlett Packard Kevin Rushforth, Sun Richard S. Wright, Real3D Hock San Lee, Microsoft

John Schimpf, Silicon Graphics Stefan Seeboth, ELSA

Mark Segal, Silicon Graphics Bob Seitsinger, S3

Min-Zhi Shao, S3 Colin Sharp, Rendition Igor Sinyak, Intel

Bill Sweeney, Sun William Sweeney, Sun Nathan Tuck, Raycer Doug Twillenger, Sun John Tynefeld, 3dfx Kartik Venkataraman, Intel

Andy Vesper, Digital Equipment

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Henri Warren, Digital Equipment / Megatek

Paula Womack, Silicon Graphics

Steve Wright, Microsoft

David Yu, Silicon Graphics

Randy Zhao, S3

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