1. David Luebke9/10/2015 CS 551 / 645: Introductory Computer Graphics David Luebke cs551@cs.virginia.edu http://www.cs.virginia.edu/~cs551

2. David Luebke9/10/2015 Administrivia Drop-add forms

3. David Luebke9/10/2015 Display Technologies: Recap Cathode Ray Tube (CRT) –Vector displays: Oscilloscope; computer draws lines on screen Pros: bright, crisp lines Cons: Just lines, and a limit on display complexity –Raster displays 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)

4. David Luebke9/10/2015 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 arrangementIn-line electron gun arrangement

5. David Luebke9/10/2015 Display Technology: Color CRTs Color CRTs have –Three electron guns –A metal shadow mask to differentiate the beams

6. David Luebke9/10/2015 Display Technology: Raster CRT (raster) pros: –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) –X-ray radiation…

7. David Luebke9/10/2015 Display Technology: LCDs 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.

8. David Luebke9/10/2015 Display Technology: LCDs 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

9. David Luebke9/10/2015 Display Technology: LCDs 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

10. David Luebke9/10/2015 Display Technology: Active-Matrix LCDs 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 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

11. David Luebke9/10/2015 Display Technology: Active Matrix LCDs Active-matrix pros: crisper with less ghosting Active-matrix cons: more expensive Today, most things seem to be active-matrix More on LCDs: More on LCDs: http://144.126.176.216/Displays/c3_s1.htm

12. David Luebke9/10/2015 Display Technology: Plasma 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

13. David Luebke9/10/2015 Display Technology Plasma Display Panel Pros –Large viewing angle –Good for large-format displays –Fairly bright Cons –Still very expensive –Large pixels (~1 mm versus ~0.2 mm) –Phosphors gradually deplete –Less bright than CRTs, using more power

14. David Luebke9/10/2015 Display Technology: DMDs Digital Micromirror Devices (projectors) –Microelectromechanical (MEM) devices, fabricated with VLSI techniques

15. David Luebke9/10/2015 Display Technology: DMDs DMDs are truly digital pixels Vary grey levels by modulating pulse length Color: multiple chips, or color-wheel Great resolution Very bright Flicker problems

16. David Luebke9/10/2015 Display Technologies: FEDs Field Emission Devices (FEDs) –Like a CRT, with many small electron guns at each pixel –Unreliable electrodes, needs vacuum –Thin, but limited in size

17. David Luebke9/10/2015 Display Technologies: Organic LED Arrays 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: Thin-film deposition or vacuum deposition process…not grown like a crystal, no high-temperature doping Thus, easier to create large-area OLEDs

18. David Luebke9/10/2015 Display Technologies: Organic LED Arrays OLED pros: –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

19. David Luebke9/10/2015 Framebuffers 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

20. David Luebke9/10/2015 Framebuffers: True-Color 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 2 24 colors Pay attention to Endian-ness How can 24-bit and 32-bit mean the same thing here?

21. David Luebke9/10/2015 Framebuffers: Indexed-Color 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

22. David Luebke9/10/2015 Framebuffers: Hi-Color 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 2 15 colors Hi-color images can exhibit worse quantization artifacts than a well-mapped 8-bit image

23. David Luebke9/10/2015 UNIX 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 We will use 2 libraries: OpenGL and Xforms –OpenGL native on SGIs; on other platforms Mesa

24. David Luebke9/10/2015 XForms Intro Xforms: a toolkit for easily building Graphical User Interfaces, or GUIs –See http://bragg.phys.uwm.edu/xformshttp://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. Quick tour now You’ll learn the details yourself in Assignment 1 (Monday)

25. David Luebke9/10/2015 The End Next up: UNIX, etc.