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The University of North Carolina at Chapel Hill
Department of Computer Science

COLLOQUIUM

Forrest Norrod
User Interface Technology Division
Hewlett-Packard

Friday, November 6, 1992
1:00 p.m.
011 Classroom, Sitterson Hall

Hardware Perspective Interpolation & Technology Trends in 3D Hardware

3D graphics users demand ever-increasing image quality and performance
from their systems.  Workstation vendors address these needs by devoting
specialized hardware to the various stages of the graphics pipeline.
The amount and nature of hardware provided for each stage of the
3D pipeline depends on cost and performance goals, but also upon technology
trends that drive a cycle long described as the 'wheel of reincarnation.'

The rasterization stage of the graphics pipeline (wherein pixel color,
texture, and depth values for transformed and lit graphics primitives
are generated) is particularly amenable to dedicated hardware.  Here the
two demands of image quality and rendering speed are in sharp conflict
with each other and the omnipresent need to reduce hardware costs.  The
traditional approach to rasterization emphasizes speed and low-cost over
image quality by using linear interpolation to produce pixel colors and
other parameters.

Linear interpolation of pixel parameters can result in serious visual
artifacts, especially when computing texture values.  Unfortunately, the
'correct' interpolation algorithm, perspective-correct interpolation, is
computationally expensive and has been difficult to implement in affordable
hardware. Recent graphics systems from Hewlett-Packard and Silicon Graphics
overcome these difficulties with advanced VLSI chip-sets that provide
high-speed perspective-correct rasterization.  Forrest Norrod from
Hewlett-Packard will discuss the architecture and algorithms of HP's
CTI (Color and Texture Interpolator) and ZI (Z Interpolator)
perspective-correct rasterization chips.  The chip set's rasterization
algorithms and the practical problems encountered in rasterizer design
will be detailled.

Rasterization hardware is almost always a feature of any graphics
workstation, but few other stages of the 3D pipeline are universally
implemented in specialized hardware.  The amount of hardware used in a
graphics system is driven by performance and cost goals, but also by
available technology.  Forrest Norrod will outline recent advances in
VLSI technology and how they are impacting the architecture of future
3D hardware.


Biographical Sketch
Forrest Norrod is a member of the technical staff of Hewlett-Packard's
User Interface Technology Division and chief architect for HP's 3D graphics
hardware.  He was one of the designers of the CTI and ZI rasterizer chip
set and architect of the CRX24Z 3D accelerator.

HOST:  Professor Turner Whitted, 962-1919, email jtw@cs.unc.