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UBI 516 Advanced Computer Graphics Aydın Öztürk [email protected] http://www.ube.ege.edu.tr/~ozturk Administrivia Syllabus • Instructor/TA coordinates • Prereqs • Texts • Assignments • Topic list Textbook • Computer Graphics with OpenGL – Third Edition – Hearn and Baker The Basics 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 Why Study Computer Graphics? Graphics is cool • I like to see what I’m doing • I like to show people what I’m doing Graphics is interesting • Involves simulation, algorithms, architecture… I’ll never get an Oscar for my acting • But maybe I’ll get one for my CG special effects Graphics is fun Graphics Applications Entertainment: Cinema Pixar: Monster’s Inc. Square: Final Fantasy Graphics Applications Entertainment: Cinema Final Fantasy (Square, USA) Graphics Applications Entertainment: Games GT Racer 3 Polyphony Digital: Gran Turismo 3, A Spec Graphics Applications Video Games Graphics Applications Medical Visualization The Visible Human Project MIT: Image-Guided Surgery Project Graphics Applications Computer Aided Design (CAD) Graphics Applications Scientific Visualization Graphics Applications Everyday Use • Microsoft’s Whistler OS will use graphics seriously • Graphics visualizations and debuggers • Visualize complex software systems Everyday use Everyday use Window system and large-screen interaction metaphors (François Guimbretière) Education Outside In (Geometry Center, University of Minnesota) Current Technologies Impact of Computers Moore’s Law Power of a CPU doubles every 18 months / 2 years Impact of Video Games (Nvidia) Number of transistors on GPU doubles each 6 months. • Three times Moore’s Law – Good article on Jen-Hsun Huang, Nvidia CEO: http://www.wired.com/wired/archive/10.07/Nvidia_pr.html Col. Steve Austin Worldwide revenues $7 Billion Man $5.6 Billion Man Retro flashback??? Lee Majors Impact of Video Games But… • Video game sales is roughly same as Hollywood box office • Americans bought $3.2 billion in VCRs and DVDs in 2002 • Total revenues to movie studios is 5 times total video game revenues Future of Consoles • 33 million PS2s (in 2002) • 3.9 million Xboxes (in 2002) – MSFT still losing lots of $$ per console • Predicted 200 million PDA/Cell game players in 2005 Display technologies Cathode Ray Tubes (CRTs) • Most common display device today • Evacuated glass bottle • Extremely high voltage CRT details • Heating element (filament) • Electrons pulled towards anode focusing cylinder • Vertical and horizontal deflection plates • Beam strikes phosphor coating on front of tube Electron Gun Contains a filament that, when heated, emits a stream of electrons Electrons are focused with an electromagnet into a sharp beam and directed to a specific point of the face of the picture tube The front surface of the picture tube is coated with small phospher dots When the beam hits a phospher dot it glows with a brightness proportional to the strength of the beam and how long it is hit CRT characteristics What’s the largest (diagonal) CRT you’ve seen? • Why is that the largest? – Evacuated tube == massive glass – Symmetrical electron paths (corners vs. center) How might one measure CRT capabilities? • Size of tube • Brightness of phosphers vs. darkness of tube • Speed of electron gun • Width of electron beam • Pixels? Display technologies: CRTs Vector Displays • Anybody remember Battlezone? Tempest? Display Technologies: CRTs Vector Displays • Early computer displays: basically an oscilloscope • Control X,Y with vertical/horizontal plate voltage • Often used intensity as Z Name two disadvantages Just does wireframe Complex scenes cause visible flicker Display Technologies: CRTs Raster Displays • Raster: A rectangular array of points or dots • Pixel: One dot or picture element of the raster • Scan line: A row of pixels Display technologies: CRTs Raster Displays • Black and white television: an oscilloscope with a fixed scan pattern: left to right, top to bottom – As beam sweeps across entire face of CRT, beam intensity changes to reflect brightness • Analog signal vs. digital display Display technologies: CRT Can a computer display work like a black and white TV? • Must synchronize – Your program makes decisions about the intensity signal at the pace of the CPU… – The screen is “painted” at the pace of the electron gun scanning the raster • Solution: special memory to buffer image with scan-out synchronous to the raster. We call this the framebuffer. • Digital description to analog signal to digital display Display Technologies: CRTs Phosphers • Flourescence: Light emitted while the phospher is being struck by electrons • Phospherescence: Light emitted once the electron beam is removed • Persistence: The time from the removal of the excitation to the moment when phospherescence has decayed to 10% of the initial light output Display Technologies: CRTs Refresh • Frame must be “refreshed” to draw new images • As new pixels are struck by electron beam, others are decaying • Electron beam must hit all pixels frequently to eliminate flicker • Critical fusion frequency – Typically 60 times/sec – Varies with intensity, individuals, phospher persistence, lighting... Display Technologies: CRTs Raster Displays • Interlaced Scanning • Assume can only scan 30 times / second • To reduce flicker, divide frame into two “fields” of odd and even lines 1/30 Sec 1/60 Sec 1/60 Sec Field 1 Field 2 Frame 1/30 Sec 1/60 Sec 1/60 Sec Field 2 Field 1 Frame Display Technologies: CRTs CRT timing • Scanning (left to right, top to bottom) – Vertical Sync Pulse: Signals the start of the next field – Vertical Retrace: Time needed to get from the bottom of the current field to the top of the next field – Horizontal Sync Pulse: Signals the start of the new scan line – Horizontal Retrace: The time needed to get from the end of the current scan line to the start of the next scan line What is a pixel? Wood chips Chrome spheres Trash Daniel Rozin – NYU: (movies) http://fargo.itp.tsoa.nyu.edu/~danny/art.html 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 • Why red, green, and blue phosphors? Delta electron gun arrangement Display Technology: Color CRTs Color CRTs have • Three electron guns • A metal shadow mask to differentiate the beams Display Technology: Raster Raster CRT pros: • Allows solids, not just wireframes • 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) CRTs – A Review • CRT technology hasn’t changed much in 50 years • Early television technology – high resolution – requires synchronization between video signal and electron beam vertical sync pulse • Early computer displays – avoided synchronization using ‘vector’ algorithm – flicker and refresh were problematic CRTs – A Review • Raster Displays (early 70s) – like television, scan all pixels in regular pattern – use frame buffer (video RAM) to eliminate sync problems • RAM – ¼ MB (256 KB) cost $2 million in 1971 – Do some math… - 1280 x 1024 screen resolution = 1,310,720 pixels - Monochrome color (binary) requires 160 KB - High resolution color requires 5.2 MB Movie Theaters U.S. film projectors play film at 24 fps • Projectors have a shutter to block light during frame advance • To reduce flicker, shutter opens twice for each frame – resulting in 48 fps flashing • 48 fps is perceptually acceptable European film projectors play film at 25 fps • American films are played ‘as is’ in Europe, resulting in everything moving 4% faster • Faster movements and increased audio pitch are considered perceptually acceptable Viewing Movies at Home Film to DVD transfer • Problem: 24 film fps must be converted to – NTSC U.S. television interlaced 29.97 fps 768x494 – PAL Europe television 25 fps 752x582 Use 3:2 Pulldown • First frame of movie is broken into first three fields (odd, even, odd) • Next frame of movie is broken into next two fields (even, odd) • Next frame of movie is broken into next three fields (even, odd, even)… 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. 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 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 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 Display Technology Plasma Display Panel Pros • Large viewing angle • Good for large-format displays • Fairly bright Cons • Expensive • Large pixels (~1 mm versus ~0.2 mm) • Phosphors gradually deplete Display Technology: DMD / DLP Digital Micromirror Devices (projectors) or Digital Light Processing • Microelectromechanical (MEM) devices, fabricated with VLSI techniques Display Technology: DMD / DLP DMDs are truly digital pixels Vary grey levels by modulating pulse length Color: multiple chips, or color-wheel Great resolution Very bright Flicker problems 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 they emit light – Thin-film deposition of organic, light-emitting molecules through vapor sublimation in a vacuum. – Dope emissive layers with fluorescent molecules to create color. http://www.kodak.com/global/en/professional/products/specialProducts/OEL/creating.jhtml 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 • Available for cell phones and car stereos Display Technologies: Organic LED Arrays OLED cons: • Not very robust, display lifetime a key issue • Currently only passive matrix displays – Passive matrix: Pixels are illuminated in scanline order, but the lack of phospherescence causes flicker – Active matrix: A polysilicate layer provides thin film transistors at each pixel, allowing direct pixel access and constant illum. Additional Displays Display Walls (Princeton) Additional Displays Stereo Video Controllers Graphics Hardware • Frame buffer is anywhere in system memory CPU Frame buffer Cartesian Coordinates System Memory System Bus Video Controller Monitor Video Controllers Graphics Hardware • Permanent place for frame buffer Frame buffer Cartesian Coordinates • Direct connection to video controller CPU System Memory Frame Buffer System Bus Video Controller Monitor Video Controllers The need for synchronization CPU synchronized System Memory Frame Buffer System Bus Video Controller Monitor Video Controllers The need for synchronization current previous • Double buffering CPU synchronized System Memory Double Buffer System Bus Video Controller Monitor Raster Graphics Systems I/O Devices System Bus Display Processor CPU System Memory Frame Buffer Video Controller Monitor Figure 2.29 from Hearn and Baker Frame Buffer Frame Buffer Figure 1.2 from Foley et al. Frame Buffer Refresh Refresh rate is usually 30-75Hz Figure 1.3 from FvDFH Direct Color Framebuffer Store the actual intensities of R, G, and B individually in the framebuffer 24 bits per pixel = 8 bits red, 8 bits green, 8 bits blue • 16 bits per pixel = ? bits red, ? bits green, ? bits blue DAC Color Lookup Framebuffer Store indices (usually 8 bits) in framebuffer Display controller looks up the R,G,B values before triggering the electron guns Color Lookup Table 0 DAC 14 Pixel color = 14 RGB Frame Buffer 1024 A Graphics System Today’s Interfaces • What is spatial dimensionality of computer screen? • What is dimensionality of mouse input? • How many degrees of freedom (DOFs) define the position of your hand in space? • Space ball