Fundamentals of Computer Graphics, 3rd Edition

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18

Peter Willemsen

Using Graphics Hardware

Throughout most of this book, the focus has been on the fundamentals underlying

computer graphics rather than on implementation details. This chapter takes a

slightly different route and blends the details of using graphics hardware with the

practical issues associated with programming that hardware.

This chapter, however, is not written to teach you OpenGL,

TM

other graphics

APIs, or even the nitty gritty specifics of graphics hardware programming. The

purpose of this chapter is to introduce the basic concepts and thought processes

that are necessary when writing programs that use graphics hardware.

18.1 What Is Graphics Hardware

Graphics hardware describes the hardware components necessary to quickly ren-

der 3D objects as pixels on your computer’s screen using specialized rasterization-

based hardware architectures. The use of this term is meant to elicit a sense of

the physical components necessary for performing these computations. In other

words, we’re talking about the chipsets, transistors, buses, and processors found

on many current video cards. As we will see in this chapter, current graphics

hardware is very good at processing descriptions of 3D objects and transforming

them into the colored pixels that fill your monitor.

One thing has been certain with graphics hardware: it changes very quickly

with new extensions and features being added continually! One explanation for

the fast pace is the video game industry and its economic momentum. Essentially

445

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446 18. Using Graphics Hardware

Geometry

Processing

Pixel

Processing

User

Program

primitives

2D screen

coordinates

Figure 18.1. The basic graphics hardware pipeline consists of stages that transform 3D

data into 2D screen objects ready for rasterizing and coloring by the pixel processing stages.

what this means is that each new graphics card provides better performance and

processing capabilities. As a result, graphics hardware is being used for tasks

that support a much richer use of 3D graphics. For instance, researchers are per-

forming computation on graphics hardware to perform ray-tracing (Purcell et al.,

2002) and even solve the Navier-Stokes equations to simulate fluid flow (Harris,

2004).

Real-Time Graphics:By

real-time graphics, we

generally mean that the

graphics-related compu-

tations are being carried

out fast enough that the

results can be viewed

immediately. Being able

to conduct operations at

60Hz is considered real

time. Once the time to

refresh the display (

frame

rate

) drops below 15Hz,

the speed is considered

more interactive than it is

real-time, but this distinc-

tion is not critical. Because

the computations need to

be fast, the equations used

to render the graphics are

often approximations to

what could be done if more

time were available.

Most graphics hardware has been built to perform a set of fixed operations

organized as a pipeline designed to push vertices and pixels through different

stages. The fixed functionality of the pipeline ensures that basic coloring, lighting,

and texturing can occur very quickly—often referred to as real-time graphics.

Figure 18.1 illustrates the real-time graphics pipeline. The important things

to note about the pipeline follow:

• The user program, or application, supplies the data to the graphics hardware

in the form of primitives, such as points, lines, or polygons describing the

3D geometry. Images or bitmaps are also supplied for use in texturing

surfaces.

• Geometric primitives are processed on a per-vertex basis and are trans-

formed from 3D coordinates to 2D screen triangles.

• Screen objects are passed to the pixel processors, rasterized, and then col-

ored on a per-pixel basis before being output to the frame buffer, and even-

tually to the monitor.

18.2 Describing Geometry for the Hardware

As a graphics programmer, you need to be concerned with how the data associ-

ated with your 3D objects is transferred onto the memory cache of the graphics

hardware. Unfortunately (or maybe fortunately), as a programmer you don’t have

complete control over this process. There are a variety of ways to place your