introducing: computer graphics chapter 1. chpater 1 -- introducing: computer graphics2 n computer...

Introducing: Computer Graphics

Chapter 1Chapter 1

Chpater 1 -- Introducing: Computer Graphics

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Computer Graphics is a branch of Computer Computer Graphics is a branch of Computer Science, but its appeal reaches far beyond it.Science, but its appeal reaches far beyond it. In its short lifetime, computer graphics has In its short lifetime, computer graphics has

attracted some of the most creative people in attracted some of the most creative people in the world to its fold.the world to its fold.

They come from all disciplines -- art, science, They come from all disciplines -- art, science, music, …music, …

In fact, since the excitement and diversity of In fact, since the excitement and diversity of computer graphics can best be conveyed by computer graphics can best be conveyed by consideration of its applications, let us take a consideration of its applications, let us take a look at several in more detail. look at several in more detail.


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1. A Few Uses of Computer Graphics Computer graphics is used today in many Computer graphics is used today in many

different areas of industry, business, different areas of industry, business, government, education, and entertainment.government, education, and entertainment.

The list is enormous, and is growing rapidly as The list is enormous, and is growing rapidly as computers with graphics capabilities become computers with graphics capabilities become commodity products.commodity products.

Here is a brief look at some of these areas:Here is a brief look at some of these areas:


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User InterfacesUser Interfaces

Interactive plotting in business, science, and Interactive plotting in business, science, and technologytechnology


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CartographyCartography

MedicineMedicine


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Computer-aided drafting and designComputer-aided drafting and design Multimedia textbooksMultimedia textbooks


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Simulation and animation for scientific Simulation and animation for scientific visualization and entertainment.visualization and entertainment.


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2. A Brief History of Computer Graphics This book concentrates on fundamental This book concentrates on fundamental

principles and techniques that were derived in principles and techniques that were derived in the past and are still applicable today -- and the past and are still applicable today -- and generally will be applicable in the future.generally will be applicable in the future.

It is easier to chronicle the changes in hardware It is easier to chronicle the changes in hardware than software, since hardware changes have had than software, since hardware changes have had a greater influence on how the field has a greater influence on how the field has developed. Thus we will begin with hardware.developed. Thus we will begin with hardware.


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2.1 Output Technology

Two basic display typesTwo basic display types Vector displays and Vector displays and Raster displaysRaster displays

Both are based on Cathode Ray Tubes (CRT’s) Both are based on Cathode Ray Tubes (CRT’s) which we will see in Chapter 4.which we will see in Chapter 4.


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Vector displays were developed in the mid-Vector displays were developed in the mid-sixties and in common use until the mid sixties and in common use until the mid eighties.eighties. Characters were made up of a sequence of Characters were made up of a sequence of

vectors or strokes. This technique was also vectors or strokes. This technique was also called a random scancalled a random scan


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Raster displays were developed in the early Raster displays were developed in the early seventies.seventies. it was based on television technology, and it was based on television technology, and

contributed more to the growth of the field than contributed more to the growth of the field than any other technology.any other technology.


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The complete image on a raster display is The complete image on a raster display is formed from the raster, which is a set of formed from the raster, which is a set of horizontal scan lines, each a row of individual horizontal scan lines, each a row of individual pixelspixels


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Since, in the raster system the entire grid of Since, in the raster system the entire grid of pixels must be stored explicitly, the availability pixels must be stored explicitly, the availability of inexpensive solid-state random-access of inexpensive solid-state random-access memory (RAM) for bitmaps in the early memory (RAM) for bitmaps in the early seventies was the breakthrough needed to make seventies was the breakthrough needed to make raster graphics the dominant hardware raster graphics the dominant hardware technology.technology.

Other Defs:Other Defs: bitmapbitmap pixmappixmap frame buffer frame buffer


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Advantages of raster over vector:Advantages of raster over vector: lower costlower cost the ability to fill areas with solid colors or the ability to fill areas with solid colors or

patterns.patterns.

Disadvantages:Disadvantages: The discrete nature of pixel representation. The discrete nature of pixel representation.

This produces jagged lines (aliasing)This produces jagged lines (aliasing) Scan conversion is neededScan conversion is needed Vector displays produce continuous smooth Vector displays produce continuous smooth

lines and curves.lines and curves.


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2.2 Input Technology

A wide range of input devices have been A wide range of input devices have been developed.developed.

Basic:Basic: keyboard, mouse, joystick, trackball,…keyboard, mouse, joystick, trackball,…

Advanced: Advanced: 3D input devices with high degrees of freedom, 3D input devices with high degrees of freedom,

and ones with feedback.and ones with feedback.


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2.3 Software Portability and Graphics Standards It used to be low-level and device dependent It used to be low-level and device dependent

packages supplied by the vendor, making it packages supplied by the vendor, making it very difficult to port the software.very difficult to port the software.

We have now moved to high-level device We have now moved to high-level device independent packages, which allow much independent packages, which allow much easier porting of software. easier porting of software.


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Graphics Software Standards:Graphics Software Standards: CORE -- 3D Core Graphics Systems -- a CORE -- 3D Core Graphics Systems -- a

specification produced by an ACM specification produced by an ACM SIGGRAPH committee in 1977.SIGGRAPH committee in 1977.

GKS - Graphical Kernel System -- (1985) GKS - Graphical Kernel System -- (1985) cleaned up and implemented the 2D portion of cleaned up and implemented the 2D portion of CORE.CORE.

GKS-3D (1988) -- implemented CORE’s 3D GKS-3D (1988) -- implemented CORE’s 3D portions. portions. Permitted the grouping of primitives (such as lines, Permitted the grouping of primitives (such as lines,

polygons, and character strings -- and their polygons, and character strings -- and their attributes) into collections.attributes) into collections.

These collections could not be nested.These collections could not be nested.


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PHIGS - Programmers Hierarchical Interactive PHIGS - Programmers Hierarchical Interactive Graphics System (1988) Graphics System (1988) PHIGS also supports a retained database of PHIGS also supports a retained database of

structures, and automatically updated the screen structures, and automatically updated the screen when the database had been altered.when the database had been altered.

PHIGS+ (1992) PHIGS+ (1992) added features for photorealistic rendering.added features for photorealistic rendering.

Other standardsOther standards PostscriptPostscript X-WindowsX-Windows OpenGLOpenGL PEXPEX

The copyright of this book.The copyright of this book.


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3. The Advantage of Interactive Graphics

Graphics provides one of the most natural means Graphics provides one of the most natural means of communicating with a computer, of communicating with a computer, since our 2D and 3D pattern recognition abilities allow since our 2D and 3D pattern recognition abilities allow

us to perceive and process data rapidly and efficiently.us to perceive and process data rapidly and efficiently.

Interactive computer graphics permits extensive, Interactive computer graphics permits extensive, high-bandwidth user-computer interaction. high-bandwidth user-computer interaction. Such interactions significantly enhance our ability to Such interactions significantly enhance our ability to

understand data, to perceive trends, and to visualize real understand data, to perceive trends, and to visualize real or imaginary objects.or imaginary objects.


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4. Conceptual Framework for Interactive Graphics The high-level conceptual framework shown The high-level conceptual framework shown

here can be used to describe almost any here can be used to describe almost any interactive graphics systeminteractive graphics system


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The three major parts of the framework are:The three major parts of the framework are: Application ModelingApplication Modeling

Calculating what is to be displayedCalculating what is to be displayed

Displaying the ModelDisplaying the Model Calling the graphics API routinesCalling the graphics API routines

Interaction HandlingInteraction Handling Handling user interaction, which will change the Handling user interaction, which will change the

model, and therefore the display.model, and therefore the display. typically an event driven looptypically an event driven loop


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Summary

Graphical interfaces have replaced textual Graphical interfaces have replaced textual interfaces as the standard means for user-interfaces as the standard means for user-computer interaction.computer interaction.

Until the late eighties, the bulk of computer-Until the late eighties, the bulk of computer-graphics applications dealt with 2D objects; 3D graphics applications dealt with 2D objects; 3D applications were relatively rare.applications were relatively rare.


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The spectacular progress of VLSI The spectacular progress of VLSI semiconductor technology also led to the semiconductor technology also led to the explosive growth of 3D accelerators and 3D explosive growth of 3D accelerators and 3D applications.applications.

Images and animations are no longer merely Images and animations are no longer merely illustrations in science and engineering -- they illustrations in science and engineering -- they have become part of the content of science and have become part of the content of science and engineering and are influencing how scientists engineering and are influencing how scientists and engineers conduct their daily work.and engineers conduct their daily work.

introducing: computer graphics chapter 1. chpater 1 -- introducing: computer graphics2 n computer...

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