Transcript presentation source

CS 551 / 645:
Introductory Computer Graphics
David Luebke
[email protected]
http://www.cs.virginia.edu/~cs551
David Luebke
3/28/2016
Administrivia
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Drop-add forms
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Display Technologies: Recap
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Cathode Ray Tube (CRT)
– Vector displays:
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Oscilloscope; computer draws lines on screen
Pros: bright, crisp lines
Cons: Just lines, and a limit on display complexity
– Raster displays
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Fixed scan pattern: left-to-right, top-to-bottom
Special memory on computer synchronized to scan out
with raster pattern of electron gun
Pros: Solid objects, image complexity only limited by
memory size and scan-out rates
Cons: Discrete sampling artifacts (aliasing), fast memory
very expensive (less true now than then)
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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
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In-line electron gun arrangement
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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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CRT (raster) pros:
– 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)
X-ray radiation…
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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:
Active-Matrix LCDs
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LCDs must be constantly refreshed, or they
fade back to their crystalline state
– Refresh applied in a raster-like scanning pattern
– Passive LCDs: short-burst refresh, followed by
long slow fade in which LCD is between On & Off
– Not very crisp, prone to ghosting
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Active matrix LCDs have a transistor and
capacitor at every cell
– FET transfers charge into capacitor during scan
– Capacitor easily holds charge till next refresh
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Display Technology:
Active Matrix LCDs
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Active-matrix pros: crisper with less ghosting
Active-matrix cons: more expensive
Today, most things seem
to be active-matrix
More on LCDs:
http://144.126.176.216/Displays/c3_s1.htm
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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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Still very 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: FEDs
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Field Emission Devices (FEDs)
– Like a CRT, with many small
electron guns at each pixel
– Unreliable electrodes, needs vacuum
– Thin, but limited in size
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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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Over half the class dreams in C and rules the
UNIX world with an iron fist
Thus, we will move the UNIX class to an
optional evening section (or two, if
necessary) led by Dale
– Getting around
– Using make and makefiles
– Using gdb
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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 (Monday)
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The End
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Next up: UNIX, etc.
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