Real-Time Rendering, Third Edition, 3rd Edition

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Chapter 1

Introduction

Real-time rendering is concerned with making images rapidly on the com-

puter. It is the most highly interactive area of computer graphics. An

image appears on the screen, the viewer acts or reacts, and this feedback

affects what is generated next. This cycle of reaction and rendering hap-

pens at a rapid enough rate that the viewer does not see individual images,

but rather becomes immersed in a dynamic process.

The rate at which images are displayed is measured in frames per sec-

ond (fps) or Hertz (Hz). At one frame per second, there is little sense of

interactivity; the user is painfully aware of the arrival of each new image.

At around 6 fps, a sense of interactivity starts to grow. An application

displaying at 15 fps is certainly real-time; the user focuses on action and

reaction. There is a useful limit, however. From about 72 fps and up,

differences in the display rate are effectively undetectable.

Watching images flicker by at 60 fps might be acceptable, but an even

higher rate is important for minimizing response time. As little as 15 mil-

liseconds of temporal delay can slow and interfere with interaction [1329].

There is more to real-time rendering than interactivity. If speed was the

only criterion, any application that rapidly responded to user commands

and drew anything on the screen would qualify. Rendering in real-time

normally means three-dimensional rendering.

Interactivity and some sense of connection to three-dimensional space

are sufficient conditions for real-time rendering, but a third element has

become a part of its definition: graphics acceleration hardware. While

hardware dedicated to three-dimensional graphics has been available on

professional workstations for many years, it is only relatively recently that

the use of such accelerators at the consumer level has become possible.

Many consider the introduction of the 3Dfx Voodoo 1 in 1996 the real

beginning of this era [297]. With the recent rapid advances in this market,

add-on three-dimensional graphics accelerators are as standard for home

computers as a pair of speakers. While it is not absolutely required for real-

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2 1. Introduction

Figure 1.1. A wonderful image from the Toy Shop demo [1246, 1247, 1249], generated at

interactive rates. (Image courtesy of Natalya Tatarchuk, ATI Research, Inc.)

time rendering, graphics accelerator hardware has become a requirement

for most real-time applications. An excellent example of the results of

real-time rendering made possible by hardware acceleration is shown in

Figure 1.1.

In the past few years advances in graphics hardware have fueled an

explosion of research in the field of interactive computer graphics. We will

focus on providing methods to increase speed and improve image quality,

while also describing the features and limitations of acceleration algorithms

and graphics APIs. We will not be able to cover every topic in depth, so our

goal is to introduce concepts and terminology, give a sense of how and when

various methods can be applied, and provide pointers to the best places to

go for more in-depth information. We hope our attempts to provide you

with tools for understanding this field prove to be worth the time and effort

you spend with our book.

1.1 Contents Overview

What follows is a brief overview of the chapters ahead.