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CS 551 / 645:
Introductory Computer Graphics
David Luebke
[email protected]
http://www.cs.virginia.edu/~cs551
David Luebke
5/23/2017
Administrivia
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Bio sheets
Name tents
Show the syllabus
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Instructor/TA coordinates
Prereqs
Text
Grading & Honor Code
Topic list
Assignments
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Questions?
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The Basics
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This course is about:
– Algorithms and data structures for presenting data
visually on a computer
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This course is not about:
– Using graphic design programs like Photoshop or
3-D Studio Max
– Using graphics APIs like OpenGL or Direct3D
(though we will learn a little OpenGL)
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The Basics
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Computer graphics: generating 2D images
of a 3D world represented in a computer.
Main tasks:
– modeling: creating and representing the geometry
of objects in the 3D world
– rendering: generating 2D images of the objects
– animation: describing how objects change in time
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Why Study Computer Graphics?
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Graphics is cool
– I like to see what I’m doing
– I like to show people what I’m doing
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Graphics is interesting
– Involves simulation, algorithms, architecture…
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Graphics is important
– Just ask Intel…
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Graphics is fun
– Roll the video…
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Graphics Applications
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Entertainment: Cinema
Universal: Jurassic Park
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Pixar: Geri’s Game
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Graphics Applications
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Entertainment: Games
id: Quake II
Cyan: Riven
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Graphics Applications
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Medical Visualization
The Visible Human Project
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MIT: Image-Guided Surgery Project
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Graphics Applications
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Computer Aided Design (CAD)
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Graphics Applications
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Scientific Visualization
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Trick Question
What’s a pixel?
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Display Technologies
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Cathode Ray Tubes (CRTs)
– Most common display device today
– Evacuated glass bottle (last
of the vacuum tubes)
– Heating element (filament)
– Electrons pulled towards
anode focusing cylinder
– Vertical and horizontal deflection plates
– Beam strikes phosphor coating on front of tube
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Display Technologies: CRTs
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Vector Displays
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Anybody remember Battlezone? Tempest?
Early computer displays: basically an oscilloscope
Control X,Y with vertical/horizontal plate voltage
Often used intensity as Z
Show: http://graphics.lcs.mit.edu/classes/6.837/F98/Lecture1/Slide11.html
Name two disadvantages
Just does wireframe
Complex scenes  visible flicker
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Display Technologies: CRTs
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Raster Displays
– Black and white television: an oscilloscope with a
fixed scan pattern: left to right, top to bottom
– Paint entire screen 30 times/sec
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Actually, TVs paint top-to-bottom 60 times/sec,
alternating between even and odd scanlines
This is called interlacing. It’s a hack. Why do it?
– To paint the screen, computer needs to
synchronize with the scanning pattern of raster
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Solution: special memory to buffer image with scan-out
synchronous to the raster. We call this the framebuffer.
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Display Technology: Color CRTs
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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?
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Display Technology: Color CRTs
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Color CRTs have
– Three electron guns
– A metal shadow mask to differentiate the beams
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Display Technology: Raster
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Raster CRT pros:
– Allows solids, not just wireframes
– Leverages low-cost CRT technology (i.e., TVs)
– Bright! Display emits light
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Cons:
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Requires screen-size memory array
Discreet sampling (pixels)
Practical limit on size (call it 40 inches)
Bulky
Finicky (convergence, warp, etc)
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Display Technology: LCDs
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Liquid Crystal Displays (LCDs)
– LCDs: organic molecules, naturally in crystalline
state, that liquefy when excited by heat or E field
– Crystalline state twists polarized light 90º.
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Display Technology: LCDs
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Liquid Crystal Displays (LCDs)
– LCDs: organic molecules, naturally in crystalline
state, that liquefy when excited by heat or E field
– Crystalline state twists polarized light 90º
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Display Technology: LCDs
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Transmissive & reflective LCDs:
– LCDs act as light valves, not light emitters, and
thus rely on an external light source.
– Laptop screen: backlit, transmissive display
– Palm Pilot/Game Boy: reflective display
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Display Technology: Plasma
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Plasma display panels
– Similar in principle to
fluorescent light tubes
– Small gas-filled capsules
are excited by electric field,
emits UV light
– UV excites phosphor
– Phosphor relaxes, emits
some other color
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Display Technology
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Plasma Display Panel Pros
– Large viewing angle
– Good for large-format displays
– Fairly bright
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Cons
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Expensive
Large pixels (~1 mm versus ~0.2 mm)
Phosphors gradually deplete
Less bright than CRTs, using more power
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Display Technology: DMDs
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Digital Micromirror Devices (projectors)
– Microelectromechanical (MEM) devices,
fabricated with VLSI techniques
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Display Technology: DMDs
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DMDs are truly digital pixels
Vary grey levels by modulating pulse length
Color: multiple chips, or color-wheel
Great resolution
Very bright
Flicker problems
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Display Technologies:
Organic LED Arrays
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Organic Light-Emitting Diode (OLED) Arrays
– The display of the future? Many think so.
– OLEDs function like regular semiconductor LEDs
– But with thin-film polymer construction:
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Thin-film deposition or vacuum deposition process…not
grown like a crystal, no high-temperature doping
Thus, easier to create large-area OLEDs
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Display Technologies:
Organic LED Arrays
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OLED pros:
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Transparent
Flexible
Light-emitting, and quite bright (daylight visible)
Large viewing angle
Fast (< 1 microsecond off-on-off)
Can be made large or small
OLED cons:
– Not quite there yet (96x64 displays…)
– Not very robust, display lifetime a key issue
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Framebuffers
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So far we’ve talked about the physical
display device
How does the interface between the device
and the computer’s notion of an image look?
Framebuffer: A memory array in which the
computer stores an image
– On most computers, separate memory bank from
main memory (why?)
– Many different variations, motivated by cost of
memory
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Framebuffers: True-Color
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A true-color (aka 24-bit or 32-bit) framebuffer
stores one byte each for red, green, and blue
Each pixel can thus be one of 224 colors
Pay attention to
Endian-ness
How can 24-bit
and 32-bit mean
the same thing
here?
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Framebuffers: Indexed-Color
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An indexed-color (8-bit or PseudoColor)
framebuffer stores one byte per pixel
This byte indexes into a color map:
How many colors
can a pixel be?
Cute trick:
color-map animation
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Framebuffers: Hi-Color
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Hi-Color is a popular PC SVGA standard
Packs R,G,B into 16-bits with 5 bits/channel:
Each pixel can be one of 215 colors
Hi-color images can exhibit worse
quantization artifacts than a
well-mapped 8-bit image
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UNIX
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You should familiarize yourself with UNIX
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Getting around: cd, mkdir/rmdir, cp/mv/rm
Using make and Makefiles
Using gdb
Carlton will be available to help with this in the lab
We will use 2 libraries: OpenGL and Xforms
– OpenGL native on SGIs; on other platforms Mesa
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XForms Intro
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Xforms: a toolkit for easily building Graphical
User Interfaces, or GUIs
– See http://bragg.phys.uwm.edu/xforms
– Lots of widgets: buttons, sliders, menus, etc.
– Plus, an OpenGL canvas widget that gives us a
viewport or context to draw into with GL or Mesa.
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Quick tour now
You’ll learn the details yourself in
Assignment 1
David Luebke
5/23/2017