Introduction to
Computer Graphics
CS 445 / 645
David Brogan
dbrogan@cs.virginia.edu
Administrivia
Syllabus
• Instructor/TA coordinates
• Prereqs
• Texts
• Assignments
• Grading & Honor Code
• Topic list
Impact of Computers
Moore’s Law
Power of a CPU doubles every 18 months / 2
years
Impact of Video Games (Nvidia)
Number of transistors on GPU doubles each 6 mos.
• Three times Moore’s Law
– Good article on Jen-Hsun Huang, Nvidia CEO:
http://www.wired.com/wired/archive/10.07/Nvidia_pr.html
Col. Steve Austin
Worldwide
revenues
$7 Billion Man
$5.6 Billion Man
Retro flashback???
Lee Majors
Impact of Video Games
But…
• Video game sales is roughly same as Hollywood boxoffice
• Americans bought $3.2 in VCRs and DVDs last yr
• Total revenues to movie studios is 5 times total video game
revenues
Future of Consoles
• 33 million PS2s
• 3.9 million Xboxes
– MSFT still losing $89 per console
• Predicted 200 million PDA/Cell game players in 2005
– Do you believe it?
Graphics Applications
Entertainment: Cinema
Square: Final Fantasy
Pixar: Monster’s Inc.
Graphics Applications
Medical Visualization
The Visible Human Project
MIT: Image-Guided Surgery Project
Graphics Applications
Everyday Use
• Microsoft’s Whistler OS will use graphics seriously
• Graphics visualizations and debuggers
• Visualize complex software systems
Graphics Applications
Scientific Visualization
Graphics Applications
Computer Aided Design (CAD)
Graphics
Applications
Entertainment: Games
GT Racer 3
Polyphony Digital: Gran Turismo 3, A Spec
The Basics
Computer graphics: generating 2D images of a 3D
world represented in a computer.
Main tasks:
• modeling: (shape) creating and representing the geometry of
objects in the 3D world
• rendering: (light, perspective) generating 2D images of the
objects
• animation: (movement) describing how objects change in time
Why Study Computer Graphics?
Graphics is cool
• I like to see what I’m doing
• I like to show people what I’m doing
Graphics is interesting
• Involves simulation, AI, algorithms, architecture…
I’ll never get an Oscar for my acting
• But maybe I’ll get one for my CG special effects
Graphics is fun
Can we learn from history?
Among the studies of natural causes and laws, it is
light that most delights its students. Among all the
great branches of mathematics, the certainty of its
demonstrations pre-eminently elevates the minds of
its investigators. Perspective, therefore, should be
preferred above all man’s discourses and
disciplines. In this subject the visual rays are
elucidated by means and demonstrations which
derive their glory nor only from mathematics but
also from physics; the one is adorned equally with
the flowers of the other.
Leonardo da Vinci (1400’s) quoting John Pecham (1200’s)
Perspective
Machines
Leonardo Again
There are some who look at the things produced by nature
through glass, or other surfaces or transparent veils.
They trace outlines on the surface of the transparent
medium… But such an invention is to be condemned in
those who do not know how to portray things without it,
no how to reason about nature with their minds… They
are always poor and mean in every invention and in the
composition of narratives, which is the final aim of this
science
Perspective
Lorenzetti
• Birth of the Virgin
• 1342
Leonardo
• The Last Supper
• 1498
Shape
We Labor On…
Light Stage – 2002
USC, Institute for
Creative
Technologies
Note: Paul
Debevec will visit
UVa in October to
talk about this and
other cool things
Display Technologies
Cathode Ray Tubes (CRTs)
• Most common display device today
• Evacuated glass bottle
• Extremely high voltage
• Heating element (filament)
• Electrons pulled towards
anode focusing cylinder
• Vertical and horizontal deflection plates
• Beam strikes phosphor coating on front of tube
Electron Gun
Contains a filament that, when heated, emits a
stream of electrons
Electrons are focused with an electromagnet into a
sharp beam and directed to a specific point of the
face of the picture tube
The front surface of the picture tube is coated with
small phospher dots
When the beam hits a phospher dot it glows with a
brightness proportional to the strength of the
beam and how often it is excited by the beam
Display Technologies: CRTs
Vector Displays
• Anybody remember Battlezone? Tempest?
Display Technologies: CRTs
Vector Displays
• Early computer displays: basically an oscilloscope
• Control X,Y with vertical/horizontal plate voltage
• Often used intensity as Z
Name two disadvantages
Just does wireframe
Complex scenes  visible flicker
Display Technologies: CRTs
Raster Displays
• Raster: A rectangular array of points or dots
• Pixel: One dot or picture element of the raster
• Scan line: A row of pixels
Display Technologies: CRTs
Raster Displays
• Black and white television: an oscilloscope with a fixed
scan pattern: left to right, top to bottom
• To paint the screen, computer needs to synchronize
with the scanning pattern of raster
– Solution: special memory to buffer image with scanout synchronous to the raster. We call this the
framebuffer.
Display Technologies: CRTs
Phosphers
• Flourescence: Light emitted while the phospher is
being struck by electrons
• Phospherescence: Light emitted once the electron
beam is removed
• Persistence: The time from the removal of the
excitation to the moment when phospherescence has
decayed to 10% of the initial light output
Display Technologies: CRTs
Raster Displays
• Frame must be “refreshed” to draw new images
• As new pixels are struck by electron beam, others are decaying
• Electron beam must hit all pixels frequently to eliminate flicker
• Critical fusion frequency
– Typically 60 times/sec
– Varies with intensity, individuals, phospher persistence,
lighting...
Display Technologies: CRTs
Raster Displays
• Interlaced Scanning
• Assume can only scan 30 times / second
• To reduce flicker, divide frame into two “fields” of odd
and even lines
1/30 Sec
1/60 Sec
1/60 Sec
Field 1
Field 2
Frame
1/30 Sec
1/60 Sec
1/60 Sec
Field 2
Field 1
Frame
Display Technologies: CRTs
Raster Displays
• Scanning (left to right, top to bottom)
– Vertical Sync Pulse: Signals the start of the next field
– Vertical Retrace: Time needed to get from the bottom of the
current field to the top of the next field
– Horizontal Sync Pulse: Signals the start of the new scan line
– Horizontal Retrace: The time needed to get from the end of
the current scan line to the start of the next scan line
Display Technology: Color CRTs
Color CRTs are much more complicated
• Requires manufacturing very precise geometry
• Uses a pattern of color phosphors on the screen:
Delta electron gun arrangement
In-line electron gun arrangement
• Why red, green, and blue phosphors?
Display Technology: Color CRTs
Color CRTs have
• Three electron guns
• A metal shadow mask to differentiate the beams
Display Technology: Raster
Raster CRT pros:
• Allows solids, not just wireframes
• Leverages low-cost CRT technology (i.e., TVs)
• Bright! Display emits light
Cons:
• Requires screen-size memory array
• Discreet sampling (pixels)
• Practical limit on size (call it 40 inches)
• Bulky
• Finicky (convergence, warp, etc)