Lec3b Theory in Computer Graphics

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Principles of Computer Graphics

Lecture 3 1


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Why we learn computer graphics?

Appreciate what we see

to develop specific engineering program

that re uires com uter ra hics

Some of theories computer graphics hasengineering applications

Trend: Engineering Computer GraphicGroup under Faculty of ME in UT, Austin

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Definition of Computer Graphics

e ers o any compu er ev ce orprogram that makes a computer

manipulating pictures. (Webopedia)

creation, storage and manipulation of

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Computer Graphics

i. Interactive

ii. Clipping

iii. Projectioniv. Hidden line or surface removal

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i. Interactive Computer Graphics

First interactive graphicssystem, Sketchpad, by IvanSutherland

Note: using CRT monitor, lightpen and function-key panel

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Interactive Computer Graphics

Touch Screen on PDA

HP I-PaqTM Wii by Nintendo

Virtual Sphere

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Desktop

Semi Immersive

Fully Immersive

e.G CAVE

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Menu and Icon: Interactive

Microsoft word with all themenu

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UI Fact

ompu er spee ncreases owever uman oesn .

Human Computer Interface Research Center

Human Interface Technolo Lab Universit of Washin ton

Group for User Interface Research (UC Berkeley)Human Computer Interaction Institute (Carnegie Mellon)Graphics, Visualization, and Usability Center (Georgia Tech)

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Cool fact on UI

90/10 rule

10% of the features using90% of the time

Xerox-First developed mouse

-First developed personnel workstation- rs eve ope over app ng mu w n ows

1985, famous lawsuit, Apple vs. Microsoft overWindows use of icons ointers etc.

Microsoft Windows is considered as a Mac imitationwith minimal improvements

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Computer Graphics

o crea e rea sm n v sua za on.

i. Interactive

ii. Clipping


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ii. Clipping

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Clipping cont

oog e ear , ren er ng scarried out when we view on certain

Why? Save memory allocation whenonl view ort is rendered or dis la ed

Problem: display actual shape anddis la sha e

Technique: display the visible partand discard the invisible art

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Clipping Technique

amous ec n que: o en an ut er an

Principle:Edges of the screen is extended to form nineregions. The central region will be the entitiesto be dis la ed.

Polygon: extra line is created

Curves: breaking the curves into segments ofstraight lines

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010100011001

e proce ure w exam ne e ver ces o

the lines using four bits codeb3 b2 b1 b0

D C

If TRUE bits = 1

b3 = ( x < xmin) vertex to the left of ADDisplay0000

1000b2 = ( x > xmax) vertex to the right of BC

b1 = (y < ymin) vertex below AB

b0 = > max vertex above CD

01100010

1010

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3D Clipping

011010011001 011000

001010001001 001000

101010101001 101000

010110010100010101 000110000100000101 100110100100100101

eg ons

6 bit outcode records results of four bounds tests:First bit: outside back plane, behind back plane

econ : ou s e ron p ane, n ron o ron p aneThird bit: outside top plane, above top planeFourth bit: outside bottom plane, below bottom planeFifth bit: outside right plane, to right of right plane

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x : ou s e e p ane, o e o e p ane


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Computer Graphics


i. Interactive

ii. Clipping


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iii. Type of projection

ara e ro ec on:

Used by engineer for measurement

erspec ve ro ec on:

Imitates eyes or camerato look more natural

SCREEN

SCREEN

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Projection in games

in games since it first used in 1982

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Computer Graphics


i. Interactive

ii. Clipping


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iv. Hidden line & Surface Removal

-

invisibleback face

invisible

back face

visible

visible

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iii. Hidden line & Surface Removal-cont

- ep

sorting all the faces (polygons) in thescene accor ng o e arges z

coordinate value of each.

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iii. Hidden line & Surface Removal-cont

0y)f(x,

222=

=Eq of the circle

tdPQ +=

Lets say eye point P = (-3,1) withVector direction of (0.8, -0.6)

.,.,.,

Therefore 096

0)(

2=+

=

tt

Qf

imaginary answer: no intersectionOne answer: tangent to the circle, visible pointTwo answer: two points,

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one v s e, one en


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Computer Graphics


i. Interactive

ii. Clipping


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v. Surface detail and texture

Point light source: provide shine on surface Ambient li ht: a li ht with uniform

brightness

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Illumination

faces called polygon, each patchhas its own normal and centeroint.

The basic principle ofillumination is light rays will

strike on each patch and the

specular

ig t wi e a sor e , re ecteor scattered.

Realism can be achieved by the

diffuse

ambient

ambient light

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Shading

Basic principle: each vertex on theol on has its own color. The color

will be interpolated as they movetoward center of the polygon

Flat shading: same color across the polygon Gourand shading: lights are computed at its vertices and

Phong lighting model: linearly interpolate a normal vector Nacross the polygon on from the normal on each vertex and it isdone for each pixel in the polygon. Then color the pixel

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Texture mapping

.

mapping is similar to process of applying patternedpaper to the object. 3D texture mapping is analogousto cravin rocess.

Visual affect or illusion is used to create realism suchsense of depth.

iClone

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Documents

Lec3b Theory in Computer Graphics