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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 Drop-add forms David Luebke 5/23/2017 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 David Luebke 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) 5/23/2017 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 David Luebke In-line electron gun arrangement 5/23/2017 Display Technology: Color CRTs Color CRTs have – Three electron guns – A metal shadow mask to differentiate the beams David Luebke 5/23/2017 Display Technology: Raster CRT (raster) pros: – Leverages low-cost CRT technology (i.e., TVs) – Bright! Display emits light Cons: – – – – – – David Luebke Requires screen-size memory array Discreet sampling (pixels) Practical limit on size (call it 40 inches) Bulky Finicky (convergence, warp, etc) X-ray radiation… 5/23/2017 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 5/23/2017 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 5/23/2017 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 5/23/2017 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 5/23/2017 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: http://144.126.176.216/Displays/c3_s1.htm David Luebke 5/23/2017 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 5/23/2017 Display Technology Plasma Display Panel Pros – Large viewing angle – Good for large-format displays – Fairly bright Cons – – – – David Luebke Still very expensive Large pixels (~1 mm versus ~0.2 mm) Phosphors gradually deplete Less bright than CRTs, using more power 5/23/2017 Display Technology: DMDs Digital Micromirror Devices (projectors) – Microelectromechanical (MEM) devices, fabricated with VLSI techniques David Luebke 5/23/2017 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 5/23/2017 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 5/23/2017 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: David Luebke Thin-film deposition or vacuum deposition process…not grown like a crystal, no high-temperature doping Thus, easier to create large-area OLEDs 5/23/2017 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 5/23/2017 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 5/23/2017 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 224 colors Pay attention to Endian-ness How can 24-bit and 32-bit mean the same thing here? David Luebke 5/23/2017 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 David Luebke 5/23/2017 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 5/23/2017 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 5/23/2017 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 5/23/2017 The End Next up: UNIX, etc. David Luebke 5/23/2017