CS 551 / 645: Introductory Computer Graphics

1. CS 551 / 645: Introductory Computer Graphics David Luebke cs551@cs.virginia.edu http://www.cs.virginia.edu/~cs551 David Luebke 9/23/2014

2. Administrivia • Drop-add forms David Luebke 9/23/2014

3. 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) David Luebke 9/23/2014

4. 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 David Luebke 9/23/2014

5. Display Technology: Color CRTs • Color CRTs have • Three electron guns • A metal shadow maskto differentiate the beams David Luebke 9/23/2014

6. 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… David Luebke 9/23/2014

7. 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. David Luebke 9/23/2014

8. 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 David Luebke 9/23/2014

9. 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 David Luebke 9/23/2014

10. 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 David Luebke 9/23/2014

11. Display Technology: Active Matrix LCDs • Active-matrix pros: crisper with less ghosting • Active-matrix cons: more expensive • Today, most things seemto be active-matrix More on LCDs: http://144.126.176.216/Displays/c3_s1.htm David Luebke 9/23/2014

12. 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 David Luebke 9/23/2014

13. 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 David Luebke 9/23/2014

14. Display Technology: DMDs • Digital Micromirror Devices (projectors) • Microelectromechanical (MEM) devices, fabricated with VLSI techniques David Luebke 9/23/2014

15. 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 David Luebke 9/23/2014

16. 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 David Luebke 9/23/2014

17. 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 David Luebke 9/23/2014

18. 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 David Luebke 9/23/2014

19. 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 David Luebke 9/23/2014

20. Framebuffers: True-Color • A true-color(aka 24-bitor 32-bit)framebufferstores one byte each for red, green, and blue • Each pixel can thus be one of 224 colors • Pay attention toEndian-ness • How can 24-bit and 32-bit mean the same thing here? David Luebke 9/23/2014

21. 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 colorscan a pixel be? • Cute trick: color-map animation David Luebke 9/23/2014

22. 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 215 colors • Hi-color images can exhibit worse quantization artifacts than a well-mapped 8-bit image David Luebke 9/23/2014

23. 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 David Luebke 9/23/2014

24. XForms Intro • 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. • Quick tour now • You’ll learn the details yourself in Assignment 1 (Monday) David Luebke 9/23/2014

25. The End • Next up: UNIX, etc. David Luebke 9/23/2014