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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
Lecture 3 2
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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
Lecture 3 3
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Computer Graphics
i. Interactive
ii. Clipping
iii. Projectioniv. Hidden line or surface removal
Lecture 3 4
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i. Interactive Computer Graphics
First interactive graphicssystem, Sketchpad, by IvanSutherland
Note: using CRT monitor, lightpen and function-key panel
Lecture 3 5
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Interactive Computer Graphics
Touch Screen on PDA
HP I-PaqTM Wii by Nintendo
Virtual Sphere
Lecture 3 6
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Desktop
Semi Immersive
Fully Immersive
e.G CAVE
Lecture 3 7
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Menu and Icon: Interactive
Microsoft word with all themenu
Lecture 3 8
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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)
Lecture 3 9
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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
Lecture 3 10
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Computer Graphics
o crea e rea sm n v sua za on.
i. Interactive
ii. Clipping
iii. Projectioniv. Hidden line or surface removal
Lecture 3 11
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ii. Clipping
Lecture 3 12
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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
Lecture 3 13
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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
Lecture 3 14
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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
Lecture 3 15
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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
Lecture 3 16
x : ou s e e p ane, o e o e p ane
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Computer Graphics
o crea e rea sm n v sua za on.
i. Interactive
ii. Clipping
iii. Projectioniv. Hidden line or surface removal
Lecture 3 17
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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
Lecture 3 18
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Projection in games
in games since it first used in 1982
Lecture 3 19
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Computer Graphics
o crea e rea sm n v sua za on.
i. Interactive
ii. Clipping
iii. Projectioniv. Hidden line or surface removal
Lecture 3 20
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iv. Hidden line & Surface Removal
-
invisibleback face
invisible
back face
visible
visible
Lecture 3 21
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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.
Lecture 3 22
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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,
Lecture 3 23
one v s e, one en
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Computer Graphics
o crea e rea sm n v sua za on.
i. Interactive
ii. Clipping
iii. Projectioniv. Hidden line or surface removal
Lecture 3 24
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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
Lecture 3 25
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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
Lecture 3 26
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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
Lecture 3 27
.
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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
Lecture 3 28